University Free State
GEEN oi IST ANDIGHEDE UIT DIE
NIJd 11111111111111111111111111111111111111111111111111111111111111111111111111111111BrRUOTEEK VER\ IYDEHWORD 34300001322456
Universiteit Vrystaat
THE IMPROVEMENT OF THE SHELF LIFE OF
VEGETABLESTHROUGHPRE-AND
POSTHARVESTTREATMENTS
By
Tilahun Seyoum Workneh
Submitted in fulfilment of the requirement for the degree of
PHILOSOPHIAE DOCTOR
in the
Department of Microbial, Biochemical and Food Biotechnology
Faculty of Natural and Agricultural Sciences
The University of the Free State
Supervisor: Prof. G. Osthoff
Co- supervisor: M. S. Steyn
November 2002
Dedication
"This work is dedicated to my father Seyoum Workneh and my mother Tafesu Dagne
for their love, encouragement and sharing the small subsistence income they were
getting from the small farm product, through the grace of God, to keep me in school
without themselves had the opportunity to be educated."
CONTENTS
Contents 1
Acknowledgement. vii
List of Tables ix
List of Figures xiv
List of Abbreviations xvii
Chapter 1 General Introduction 1
1.1. Background 1
1.2. Objective 5
Chapter 2 Literature Review 6
Abstract 6
2.1. Introduction 6
2.2. Development physiology of fruit and vegetables 7
2.2.1. Development physiology of tomatoes 7
2.2.2. Development physiology of carrots ~ 8
2.3. Preharvest treatments ofvegetables 9
2.3.1. Effect of preharvest factors on storage quality of vegetables 9
2.3.1.1. Soil plant system and fertiliser practice 9
2.3.1.2. Effect of environmental factors on vegetable quality .. 12
2.3.1.3. Water management. 12
2.3.1.4. Hormone treatment. 13
2.3.1.5. Communication Catalization (ComCat'") treatment 15
2.4. Postharvest physiology of fruit and vegetables 16
2.4.1. Respiration 16
2.4.2. Temperature quotient ofrespiration 18
2.4.3. Ethylene production and effects 19
2.4.4. Transpirationalloss 20
2.4.5. Postharvest physiological disorder 21
2.4.6. Chemical and biochemical changes during ripening and
storage 22
2.4.6.1. Carbohydrates 22
2.4.6.2. Organic acids 24
2.4.6.3. Enzyme activity 24
2.4.7. Postharvest microbiology of fruit and vegetables 26
2.5. Post-harvest handling and storage 28
2.5.1. Pre-packaging treatments 28
2.5.1.1. Postharvest disease control 28
2.5.1.2. Electrochemically activated water (anolyte water) 31
2.5.2. Packaging 32
2.5.2.1. Controlled atmosphere packaging 32
2.5.2.2. Modified atmosphere packaging 34
2.5.2.2.1. Physiological changes 35
2.5.2.2.2. Chemical and biochemical changes 36
2.5.2.2.3. Microbiological changes 38
2.5.2.2.4. Postharvest factors affecting MAP 39
2.5.2.2.4.1. Commodity factors 39
2.5.2.2.4.2. Environmental factors 41
2.5.2.3. Packaging films ·········..··..······· 42
2.5.3. Progress on evaporative cooling ofvegetables .45
2.6. Summary 47
Chapter 3 Effect of pre- and postharvest treatments on physiological, chemical
and microbiological qualities of stored carrots 50
Abstract 50
3.1. Introduction ·..·········································5·1·······
3.2. Materials and Methods ·· ············· 52
3.2.1. Carrot production 52
3.2.2. Postharvest treatment 53
3.2.3. Modified atmosphere packaging 54
3.2.4. Gas sampling and analysis ··············· 54
3.2.5. Physiological weight loss 55
3.2.6. Chemical analysis ··········· 55
3.2.6.1. Total soluble solids 55
3.2.6.2. Free sugar analysis 56
3.2.6.3. Total available carbohydrate 56
3.2.6.4. Ascorbic acid analysis ··········· 56
3.2.6.5. Peroxidase activity 57
3.2.7. Microbiological analysis ········ 57
3.2.8. Subjective quality attributes 58
3.2.9. Experimental design and data analysis ·58
3.3. Results 59
3.3.1. Headspace gas concentration ········· 59
3.3.2. Physiological weight loss 63
3.3.3. Chemical changes 65
11
3.3.3.1. Total soluble solid 65
3.3.3.2. Total available carbohydrate 68
3.3.3.3. Free sugar 71
3.3.3.4. Total soluble sugar 77
3.3.3.5. Sucrose-hexose ratio 80
3.3.3.6. Ascorbic acid content.. 80
3.3.3.7. Peroxidase activity 82
3.3.4. Microbiological changes 86
3.3.5. Subjective quality attributes 92
3.4. Discussions 97
Chapter 4 Effect of pre- and postharvest treatments on physiological, chemical
and microbiological qualities of stored tomatoes 111
Abstract 111
4.1. Introduction 112
4.2. Materials and Methods 114
4.2.1. Tomato production 114
4.2.2. Postharvest treatment 114
4.2.3. Modified atmosphere packaging 115
4.2.4. Gas sampling and analysis 115
4.2.5. Physiological weight Loss 115
4.2.6. Chemical and biochemical analysis 116
4.2.6.1. pH and titratabie acidity 116
4.2.6.2. Total soluble solids 116
4.2.6.3. Free sugar 116
4.2.6.4. Ascorbic acid analysis 117
4.2.6.5. Peroxidase activity 117
4.2.6.6. Polygalacturonase activity 117
4.2.7. Microbiological analysis 118
4.2.8. Subjective quality analysis 118
4.2.9. Experimental design and data analysis 118
4.3. Results 119
4.3.1. Headspace gas concentration 119
4.3.2. Physiological weight Loss 124
4.3.3. Chemical and biochemical changes 127
4.3.3.1. pH and titratable acidity 127
4.3.3.2. Total soluble solid 131
4.3.3.3. Free sugar 133
4.3.3.4. Total soluble sugar 139
111
4.3.3.5. Sucrose equivalent 140
4.3.3.6. Sucrose-hexose ratio 142
4.3.3.7. Sugar-acid ratio 144
4.3.3.8. Ascorbic acid analysis : ···.· 145
4.3.3.9. Peroxidase activity 147
4.3.3.10. Polygalacturonase activity 149
4.3.4. Microbiological changes 151
4.3.5. Subjective quality analysis 157
4.4. Discussion 159
Chapter 5 Effect of preharvest treatment and forced ventilation evaporative
cooling on carrots 174
Abstract 174
5.1. Introduction ····································1·7··4···
5.2. Materials and Methods ··········· 176
5.2.1. Evaporative cooling chamber 176
5.2.2. Temperature and relative humidity measurement 178
5.2.3. Vegetable production ········ 178
5.2.4. Postharvest treatment 179
5.2.5. Physiological weight loss 180
5.2.6. Moisture content · ········ 180
5.2.7. Juice content ·· 181
5.2.8. Chemical analysis ·············· 181
5.2.8.1. pH and total soluble solid ··········181
5.2.8.2. Sugar analysis ············· 181
5.2.9. Microbiological analysis ·············· 182
5.2.9.1. Total aerobic bacteria and fungi 182
5.2.10. Subjective quality analysis 183
5.2.11. Data analysis ······· 183
5.3. Result and Discussions 183
5.3.1. Temperature and relative humidity ······183
5.3.2. Physiological weight loss, moisture and juice content.. 187
5.3.3. Chemical changes ··········· 191
5.3.3.1. Total soluble solid ·· ················· 191
5.3.3.2. pH ·..···· 193
5.3.3.3. Sugar analysis ············· 194
5.3.4. Microbiological changes 197
5.3.4.1. Total aerobic bacteria ··················· 197
5.3.4.2. Total moulds and yeast.. ···198
IV
5.3.5. Subjective quality analysis 200
5.4. Conclusions 202
Chapter 6 Effect of preharvest treatment and forced ventilation evaporative
cooling on tomatoes 204
Abstract 204
6.1. Introduction 204
6.2. Materials and methods 205
6.2.1. Vegetable production ······· 205
6.2.2. Postharvest treatment 206
6.2.3. Temperature and relative humidity measurement 207
6.2.4. Physiological weight loss, moisture and juice content 207
6.2.5. Chemical analysis ·········· 207
6.2.5.1. pH, total titratable acidity and total soluble solid 207
6.2.5.2. Sugar analysis ··············· 207
6.2.6. Microbiological analysis ··············· 207
6.2.6.1. Total aerobic bacteria and fungi 207
6.2.7. Subjective quality analysis 207
6.2.8. Data analysis ······ 208
6.3. Results and Discussions 208
6.3.1. Temperature and relative humidity ······208
6.3 .2. Physiological weight loss, moisture and juice content 211
6.3.3. Chemical changes 214
6.3.3.1. Total soluble solid ··················· 214
6.3.3.2. pH ······ 216
6.3.3.3. Total titratable acidity 218
6.3.3.4. Sugar changes during storage ·········2·20
6.3.4. Microbiological changes 222
6.3.4.1. Total aerobic bacteria ····················222
6.3.4.2. Total moulds and yeasts 224
6.3.5. Subjective quality analysis 225
6.4. Conclusions ··· 227
Chapter 7 General Discussions and Conclusions 230
REFERENCES 241
SUMMARY 275
OPSOMMING 277
v
Appendix A Significance .
Appendix A.I. Analysis of variance for the effects of storage time and the
interactive effects of storage time with pre- and postharvest treatments
on the qualities of tomatoes during storage at 13oe and room
temperature for 30 days 279
Appendix A.2. Analysis of variance for the effects of storage time and the
interactive effects of storage time with pre- and postharvest treatments
on the qualities of carrot during storage at 1°C and room temperature
for 28 days ······································2·8··0···
Appendix A.3. Analysis of variance for the effects of storage time and the
interactive effects of storage time with pre- and postharvest treatments
on the qualities of tomatoes during storage inside the evaporative
cooling chamber and ambient temperature 281
Appendix A.4. Analysis of variance for the effects of storage time and the
interactive effects of storage time with pre- and postharvest treatments
on the qualities of carrots during storage at ambient and inside the
evaporative cooler 282
vi
ACKNOWLEDGEMENTS
1 want to give praise, honor and glory to my heavenly Father, who enabled me to
complete this study through his grace, the Holy Sprit guidance, encouragement, and
strength. "1 know that you can do all things; no plan of yours can be thwarted" (Job
42:2). 1 want to thank him and praise His holy name for all He has done for me up to
this stage.
1 am sincerely grateful to Professor G. Osthoff, Department of Microbiology,
Biochemistry and Food Science, The University of the Free State, for his supervision,
enthusiastic interest, invaluable support, friendly advice, and his contribution to the
revision of the dissertation throughout this project.
1 am also sincerely grateful to Me M.S. Steyn, Department of Microbiology,
Biochemistry and Food Science, The University of the Free State, for her eo-
supervision, friendly advice, support and her contribution to the revision of the
dissertation.
I wish to sincerely thank Dr. Celia Hugo, Department of Microbiology, Biochemistry
and Food Science, The University of the Free State, for her advice on microbiological
analysis technique.
I wish to thank Professor J.C. Pretorius, Department of Soil, Crop and Climate
Sciences, The University of the Free State, for his assistance during the planning of the
study, and Mrs G. M. Engelbrecht for her assistance during the vegetable production.
I wish to thank Dr. E. Joubert, ARC Infruitec-Nietvoorbij, Stellenbosch, for her
advice during the planning of the study.
vn
I also wish to thank Mr. W. Kruger for his assistance during the production of carrots
and tomatoes on his farm.
I also wish to sincerely thank Professor D. Litthhaur, Head Department of
Microbiology, Biochemistry and Food Science, The University of the Free State, for
making laboratory facilities available.
I would like to thank Mr. P. Botes, Department of Microbiology, Biochemistry and
Food Science, The University of the Free State, for his invaluable assistance in
chromatography analysis.
I wish to thank Mrs Rosalie Hunt, for her assistance in the provision of laboratory
reagents and for keeping the laboratory running and Mrs A. Vander Westhuizen,
Secretary of Food Science for her assistance and some very valuable help throughout
the study period.
I would like to thank Mrs Linda de Wet, Department of Soil, Crop and Climate
Sciences for her assistance with the climatic data during vegetable production and
storage.
I also wish to thank The International Student Office, The University of the Free
State, for their service and facilitation throughout the study period.
I would like to thank The Alemaya University, Ethiopia, for their financial assistance
under The Agricultural Research Training Project (ARTP).
I would also like to express my gratitude to my parents Seyoum Workneh and Tafesu
Dagne, to my parents-in-law, Ayelech Abate and Tesfaye Kidane, to my brother Million
Seyoum, sisters and brothers for their support and encouragement throughout this study.
I wish to express my sincere gratitude and appreciation to my wife Tsion Tesfaye
and my son Dawit Tilahun for their interest, encouragement, support, love and most of
all for their dedication in my absence from home during the period ofthis study.
Vlll
LIST of TABLES
Table 2.1. Permeability characteristics of several plastic films with potential for
use as MAP of fresh and lightly processed produce 43
Table 3.1. Changes in physiological weight loss of carrots subjected to pre- and
postharvest treatments and stored in air at IOC and room temperature
(RT) for 50 days 64
Table 3.2. Changes in total soluble solid (TSS) of carrots subjected to both pre
and postharvest treatment and stored at IOC and room temperature (RT)
for 28 days 66
Table 3.3. Changes in total available carbohydrate contents of carrots subjected
to both pre-and postharvest treatments and stored at IOC and room
temperature (RT) for 28 days 69
Table 3.4. (a). Changes in sucrose content of carrots subjected to both pre- and
postharvest treatments and stored at IOC and room temperature (RT)
for 28 days 72
Table 3.4. (b). Changes in glucose content of carrots subjected to both pre- and
postharvest treatments and stored at IOC and room temperature (RT)
for 28 days 74
Table 3.4. (c). Changes in fructose content of carrots subjected to both pre- and
postharvest treatments and stored at IOC and room temperature (RT)
for 28 days 76
Table 3.5. Changes in total sugar content of carrots subjected to both pre- and
postharvest treatments and stored at IOC and room temperature (RT)
for 28 days 78
Table 3.6. Changes in sucrose-hexose ratio of carrots subjected to both pre- and
postharvest treatments and stored at 1°C and room temperature (RT)
for 28 days 81
ix
Table 3.7. Changes in ascorbic acid content (AA) of carrots subjected to both
pre- and postharvest treatment and stored at 1°C and room temperature
(RT) for 28 days 83
Table 3.8. Total aerobic bacteria populations on carrots dipped in chlorinated
and anolyte water and storage at 1°C and room temperature (RT) for 28
days 87
Table 3.9. Changes in the population ofyeasts and mold in carrots subjected to
different disinfecting treatments and stored at 1°C and room
temperature (RT) for 28 days 89
Table 3.10. Total coliform populations on carrots dipped in chlorinated and
anolyte water and storage at 1°C and room temperature (RT) for 28
days 91
Table 3.11. Changes in descriptive quality attributes of pre- and postharvest
treated carrots after 28 days of storage at 1°C and room temperature
(RT) 93
Table 4.1. Changes in physiological weight loss (%) of tomatoes packaged in
Xtend® film or unpackaged and stored at 13°C and room temperature
(RT) for 30 days (n = 3 over four storage times) 125
Table 4.2. Changes in pH value of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days
(n = 3 over four storage times) 128
Table 4.3. Changes in titratable acidity oftomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days
(n = 3 over four storage times) 130
Table 4.4. Changes in total soluble solid (TSS) of tomatoes packaged in
Xtend'" film or unpackaged and stored at 13°C and room temperature
(RT) for 30 days (n = 3 over four storage times) 132
Table 4.5 (a). Changes in sucrose content oftomatoes packaged in Xtend® film
or unpackaged and stored at 13°C and room temperature (RT) for 30
days (n = 3 over four storage times) 135
x
Table 4.5 (b). Changes in glucose content of tomatoes packaged inXtend® film
or unpackaged and stored at 13°C and room temperature (RT) for 30
days (n = 3 over four storage times) ················· 137
Table 4.5 (c). Changes in fructose content oftomatoes packaged in Xtend® film
or unpackaged and stored at 13°C and room temperature (RT) for 30
days (n = 3 over four storage times) ·················· 138
Table 4.6. Changes in total sugar content of tomatoes packaged in Xtend® film
or unpackaged and stored at 13°C and room temperature (RT) for 30
days (n = 3 over four storage times) ················· 139
Table 4.7. Changes in sucrose equivalent (g/100g fresh weight) of tomatoes
packaged in Xtend® film or unpackaged and stored at 13°C and room
temperature (RT) for 30 days (n = 3 over four storage times) 141
Table 4.8. Changes in sucrose-hexose ratio of tomatoes packaged in Xtend®
film or unpackaged and stored at 13°C and room temperature (RT) for
30 days (n = 3 over four storage times) ····················· 143
Table 4.9. Changes in sugar-acid ratio of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days
(n = 3 over four storage times) ··········· 144
Table 4.10. Changes in ascorbic acid of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days
(n = 3 over four storage times) 146
Table 4.11. Changes in total aerobic bacteria populations in tomatoes packaged
in Xtend® film or unpackaged and stored at 13°C and room temperature
(RT) for 30 days (n = 3 over four storage times) 152
Table 4.12. Changes in yeast and mold populations in tomatoes packaged in
Xtend® film or unpackaged and stored at 13°C and room temperature
(RT) for 30 days (n = 3 over four storage times) : 154
Table 4.13. Changes in total coliform populations in tomatoes packaged in
Xtend® film or unpackaged and stored at 13°C and room temperature
(RT) for 30 days (n = 3 over four storage times) 156
Xl
Table.4.14. Changes in percentage' marketability of tomatoes packaged in
Xtend® film or unpackaged and stored at 13°C and room temperature
(RT) for 30 days (n = 3 over four storage times) 158
Table 5.1. The climatic conditions of the study site during sample carrot
production (2001) · · ·..· 179
Table 5.2. Changes in physiological weight loss of carrot stored in evaporative
cooling chamber and ambient temperature for 24 days 187
Table 5.3. Changes in moisture content of carrot stored in evaporative cooling
chamber and ambient temperature for 24 days 189
Table 5.4. Changes in juice content of carrot stored in evaporative cooling
chamber and ambient temperature for 24 days 190
Table 5.5. Changes in TSS of carrot stored in evaporative cooling chamber and
ambient temperature for 24 days 192
Table 5.6. Changes in pH of carrots stored in evaporative cooling chamber and
ambient temperature for 24 days · 193
Table 5.7. Changes in reducing, non-reducing and total sugar contents of carrot
stored in evaporative cooling chamber and ambient temperature for 24
days 195
Table 5.8. Populations of total aerobic bacteria in carrots packaged or
unpackaged and stored in evaporative cooling chamber or at ambient
temperature 198
Table 5.9. Populations of moulds and yeasts in carrots packaged or unpackaged
and stored in evaporative cooling chamber or at ambient temperature 200
Table 5.10. Percentage marketable carrots of different treatments after 4, 8, 12,
16, 20 and 24 days of storage at evaporative cooling and ambient
temperatures 201
Table 6.1. Changes in physiological weight loss of carrot stored in evaporative
cooling chamber and ambient temperature for 24 days 212
Table 6.2. Changes in juice content of tomatoes stored in evaporative cooling
chamber and ambient temperature for 24 days :213
xii
Table 6.3. Changes in total soluble solids of tomatoes stored in evaporative
cooling chamber and ambient temperature for 24 days 215
Table 6.4. Changes in pH of tomatoes subjected to different pre- and
postharvest treatments and stored in evaporative cooling chamber and
ambient temperature for 24 days 217
Table 6.5. Changes in total titratabie acidity of tomatoes subjected to different
pre- and postharvest treatments and stored in evaporative cooling
chamber and ambient temperature 219
Table 6.6. Changes in reducing, non-reducing and total sugar contents of
tomatoes stored in the evaporative cooling chamber and ambient
conditions for 24 days 221
Table 6.7. Populations of total aerobic bacteria in tomatoes packaged or
unpackaged and stored in evaporative cooling chamber or at ambient
temperature 223
Table 6.8. Populations of moulds and yeasts in tomatoes packaged or
unpackaged and stored in the evaporative cooling chamber or at
ambient temperature ··································2·2··4···
Table 6.9. Percentage marketable ComCat® treated and control tomatoes
subjected to different treatments after 4, 8, 12, 16, 20 and 24 days of
storage at evaporative cooling and ambient temperatures 226
X111
LIST of FIGURES
Figure 3.1. Changes in 02 content (%) in packages of carrots in Xtend® film
stored at 1°C and room temperature (RT) for 28 days (n = 3 over six
storage times) 60
Figure 3.2. Changes in C02 content (%) in packages of carrots in Xtend® film
stored at 1°C and room temperature (RT) for 28 days (n = 3 over six
storage time) ·······························6··1····
Figure 3.3. Changes in N2 content (%) in packages of carrots in Xtend® film
stored at 1°C and room temperature (RT) for 28 days (n = 3 over six
storage time) ································6··2····
Figure 3.4. Changes in levels of activities of peroxidase in carrots subjected to
different pre- and postharvest treatments and stored at 1°C and room
temperature (RT) for 28 days 85
Figure 3.5. The effect of chlorinated and anolyte water dipping treatment on
the visual appearance quality of carrots stored at 1°C for 8 days (above)
and 16 days (below), showing the etched surface of the chlorine treated
carrots 94
Figure 3.6. The effect of chlorinated and anolyte water dipping treatment on
the visual appearance quality of carrots stored at room temperature
(RT) for 8 days (above) and 16 days (below), showing the etched
surface of the chlorine treated carrots ··············.·.·9· 5
Figure 3.7. The effect of chlorinated and anolyte water dipping treatment on
the visual appearance quality of carrots stored at room temperature
(RT) for 30 days, showing the levels of decay and mold growth on the
chlorine treated carrots ··· ·.························9·6···
XIV
Figure 4.1. Changes inO2 content (%) in packages oftomatoes in Xtend® film
stored at 13°C and room temperature (RT) for 30 days (n = 3 over five
storage times) 120
Figure 4.2. Changes in C02 content (%) in packages of tomatoes in Xtend®
film stored at 13°C and room temperature (RT) for 30 days (n = 3 over
five storage time) ·· 121
Figure 4.3. Changes in N2 content (%) in packages of tomatoes in Xtend® film
stored at 13°C and room temperature (RT) for 30 days (n = 3 over five
storage time) 123
Figure 4.4. Changes in peroxidase of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days
(n = 3 over four storage times) 148
Figure 4.5. Changes in polygalacturonase activities of tomatoes packaged in
Xtend® film or unpackaged and stored at 13°C and room temperature
(RT) for 30 days (n = 3 over four storage times) 150
Figure 5.1. Schematic diagram of an experimental evaporative cooler for
vegetable storage under hot arid and semi- arid conditions 177
Figure 5.2. (a)-(g). Temperature (OC) and relative humidity (%) of the
environmental air and the air inside the evaporative cooling during
carrot storage at 6 am (a), 8 am (b), 10 am (c), 12 am (d), 2 pm (e), 4
pm (f) and 6 pm (g) 185
Figure 5.3. (a). The effect of daytime on the average environmental and
evaporative cooler temperatures (OC)during storage of tomatoes 186
Figure 5.3. (b). The effect of daytime on the average environmental and
evaporative cooler relative humidity (%) during storage oftomatoes 186
Figure 6.1. (a)-(g). Temperature (OC) and relative humidity (%) of the
environmental air and the air inside the evaporative cooling during
tomato storage at 6 am (a), 8 am (b), 10 am (c), 12 am (d), 2 pm (e), 4
pm (f) and 6 pm (g) 209
Figure 6.2. (a). The effect of daytime on the average environmental and
evaporative cooler temperatures (OC)during storage of tomatoes 210
xv
Figure 6.2. (b). The effect of daytime on the average environmental and
evaporative cooler relative humidity (%) during storage oftomatoes 210
XVi
LIST of ABBREVIATIONS
Abbreviation Description
AA Ascorbic acid
ABS Absorbancy
ANOVA Analysis of variance
C.V. Coefficient of variation
CFU Colony forming unit
ComCat Communication and Catalization
e.g. For example
EC Evaporative cooling
g Gram
HDPE High-density polyethylene
i.e. That is
kg Kilogram
LDPE Low-density polyethylene
LL DPE Linear low density polyethylene
LSD Least significance difference
MAP Modified atmosphere packaging
MDPE Medium-density polyethylene
mg Milligram
ml Milliliter
MSE Mean square error
NS Not significant
P Significance level
PG Polygalacturonase activity
POX Peroxidase activity
PP Polypropylene
PS Polystyrene
PVC Polyvinylchloride
xvii
PVC Polyvinylchloride, plasticized
PVDC Polyvinylidine chloride
PWL Physiological weight loss
RH Relative humidity
S.E. Standard error
SH Sucrose to hexose ratio
TAC Total available carbohydrate
TSS Total soluble solid
TTA Total titratable acidity
VA Ethylene vinyl acetate copolymer
XVlll
CHAPTERl
GENERAL INTRODUCTION
1.1. Background
Research results suggested that selection and careful handling of food products
determine the quality of fresh produce (Zagory and Kader, 1988). Harvesting products at
optimum maturity, maintaining higher sanitation standards, decreasing injury incidence
and maintaining optimum environmental conditions will guarantee excellent postharvest
quality. Value that does not exist at harvesting time, however, cannot be added with the
correct postharvest handling procedures.
The response of fruit and vegetables during storage to postharvest factors in part
depends on preharvest practices (Salunkhe et ai., 1991). Therefore, it seems that
preharvest operations or treatments that are applied to improve yield and quality of
vegetables play an important role in postharvest quality changes. Preharvest treatments
have had significant effects on the postharvest quality of vegetables (Bialezyk et ai.,
1996; Gao et ai., 1996 and Carmer et al., 2001). Recently, a preharvest treatment called
Communication Catalysation (Comf'at'") has been developed and it was shown in
different countries to result in increased yields of vegetables (Huster, 2001). Unlike the
other preharvest chemical treatments at agricultural input level, the most important
advantage of ComCat® is that it is both environmentally and ecologically friendly.
ComCat® consists of biocatalysts of plant origin and induces resistance via activating
plant 'defence mechanisms against pathogens, and biotical and abiotical stress factors.
ComCat® treatment is an alternative to chemical treatments and can fit into future
research trends to have a balance between yield and ecologisation. This treatment makes
crops stronger and competent without destroying the other plant species in the ecology.
However, at present there is no information on the postharvest quality aspects of the
high harvest yield ComCat® treated vegetables, and the following questions arise:
General Introduction
• How do these complex plant growth regulators and natural metabolites affect the
quality of vegetables at harvest?
• How do ComCat® treated vegetables perform when subjected to different
postharvest treatments and during storage?
The effect of combined preharvest ComCat® and postharvest (prepackaging and
packaging) treatments on quality parameters should therefore be investigated to
understand postharvest performance of these ComCat® treated vegetables.
It would not be possible to investigate the effect of ComCat® treatment on
postharvest performance on a wide variety of vegetables at once. Representatives of the
vegetable part of a plant i.e. root, stem or leaf, and also the fruit part should be
investigated first. The selection should also be from vegetables, which are of economic
importance, in developed as well as developing countries, and should be ones that are
commonly used for pre-packaged storage for a few weeks. From several options, carrots
and tomatoes were selected as subjects of this study.
Regarding postharvest techniques, the current growing demand for "fresh-like"
quality and shelf-stable intact vegetables has spurred the development of many
innovations, especially in the packaging sector. Among these, controlled-atmosphere
storage and modified atmosphere packaging are the dominant means of storage.
Packaging of fresh and lightly processed vegetables has several benefits: easy
consumer packaging, protection from damage, reduction of water loss, shrinkage, and
wilting, reduction of decay, reduction of physiological disorder (chilling damage),
reduction of ripening and senescence processes, reduction of growth and sprouting and
control of insects in some commodities (Gibbons, 1973; Kelsey, 1978; Crosby, 1981;
Kumar and Balasubrahanyam, 1984; Myers, 1989).
Modified atmosphere packaging (MAP) involves depletion of O2 and emanation of
CO2 within a sealed plastic packaging headspace, which controls the metabolism. Decay
is also reduced due to the prevention of moisture condensation (Zagory and Kader,
1988). MAP is therefore a very convenient way to protect vegetables during storage.
2
General Introduction
The quality properties of packaged vegetables are, however, governed by cultivars,
growing conditions and maturity stage at harvest (Cameron and Reid, 1982). Therefore,
an optimum packaging system is required for new cultivars and products grown under
different treatment conditions. It would therefore be important to investigate the effect
of MAP storage on ComCat® treated vegetables.
The microbial load associated with vegetables during storage also plays an important
role on quality deterioration and is one of the postharvest quality parameters (Brackett,
1992). The initial microbial load of vegetables from the field determines the microflora
of vegetables during storage periods if one assumes good sanitation prevails during and
after harvest. The shelf life and protection of microbial spoilage of vegetables stored
with MAP can be improved by the application of any treatment that can reduce the
initial microbial load (Bolin ef al., 1977; Brackett, 1992). The present research trend is
towards developing environmentally and ecologically safe disinfectants for biocontrol.
In most of the cases, vegetables are washed with cold chlorinated water prior to
packaging or are disinfected with different types of chemicals. Several workers showed
the effectiveness of chlorine solution in killing or reducing the microbiological flora and
pathogenic organisms (Escudero ef al., 1999; Beuchat ef al., 2001; Li ef al., 2001;
Ukuku and Sapers; 2001). Furthermore, emphasis was given to postharvest
microbiological changes without due consideration to the possible effect of chlorine
solutions on the postharvest physiology and biochemical changes of fruits and
vegetables. Some chemicals are not easily available in the marketplace while others
need technical knowledge for use. Simons and Sanguansri (1997) in Delaguis ef al.
(1999) reported that even though alternatives or modified treatments have been
proposed, none have yet gained widespread acceptance. Recently a product,
electrochemically activated water (anolyte), based on a Russian development, was
developed for use in dental unit water lines (STEDS, Radical Waters, Midrand, South
Africa). The original development was applied in fields varying from agriculture,
cooling towers, swimming pools, dermatology, dressing and cleaning of wounds and
3
General Introduction
disinfecting of instruments (Leonov , 1997; Bakhir, 1997; Prilutski and Bakhir, 1997).
Anolyte contains free radicals and is considered totally harmless to human tissue, yet
highly microbiocidal. It was further established that anolyte solutions return to a stable,
inactive state of pure water, within a period of 48 hours after production, therefore being
environmentally friendly. Since the effect of chlorine treatment on postharvest
physiology and biochemical changes of fruits and vegetables has not yet been studied,
the question arises what the effect of anolyte would be on these properties. Anolyte and
chlorine as disinfecting treatments should therefore be investigated in parallel to add to
the optimisation of postharvest handling of vegetables in general, and to investigate
postharvest performance of ComCat® treated vegetables when subjected to these
treatments in specific.
In underdeveloped countries there is a need for higher crop productivity, followed by
appropriate means of reducing losses after harvest, aiming at sufficient food security and
nutrition for their society. Fruits and vegetables are major food crops rich in vitamin C,
magnesium and sometimes in carbohydrate, compared to the percentage of total food
supply (Salunkhe et al., 1991). Obviously, improving productivity, reduction of
postharvest losses and maintaining quality after harvest should be the main strategy in
underdeveloped regions of the world.
The second part of this study, therefore, deals with the appropriate postharvest
technologies as a potential means to reduce the excessive losses of ComCat® treated and
control vegetables after harvest in developing countries like Ethiopia.
Agriculture is the major branch of the Ethiopian economy. The climatic and soil
conditions of Ethiopia allow cultivation of a wide range of fruit and vegetable crops. It
has a vast potential for the internal market for fresh fruits and vegetables, primarily in
densely populated urban areas, such as the Addis Ababa region, and is also located close
to important foreign markets, such as Saudi Arabia, Djibouti, Somalia, etc.
However, growing and marketing of fresh produce in Ethiopia are complicated by
high postharvest losses which are estimated as high as 25 - 35% of the produced volume
4
General Introduction
for vegetables (Agonafir, 1991) and may reach even higher figures for fruits. These
losses discourage farmers from producing and marketing fresh produce and limit the
urban consumption of fresh vegetables to as low as 25-30% of that in the Western world
(Wolde, 1991).
Lack of proper packaging is one of the major causes of postharvest losses of fresh
fruits and vegetables in Ethiopia (Wolde, 1991). The lack of modem refrigeration and
packaging house facilities in these countries results in severe food losses. A cooling
chamber that works on the principle of evaporative cooling was developed to counter
this problem (Seyoum and W/Tsadik, 2000). This chamber was shown to maintain
temperature and also control humidity. Should ComCat® treatment also be able to
increase yield of vegetables in Ethiopia, it would be important to know what the
postharvest performance of these vegetables would be under evaporative cooling at
storage temperatures other than the optimised refrigeration temperatures.
1.2. Objective
1. Investigations of the effect of preharvest ConrCat'" treatment on postharvest quality
of stored carrots and tomatoes.
2. Investigation of the effect ofpre-packaging and storage treatments (washing, dipping
in anolyte and chlorine supplemented water) on the quality of preharvest ComCat®
treated and untreated carrots and tomatoes.
3. Investigation of the storage quality of preharvest ComCat® treated carrots and
tomatoes using modified atmosphere packaging.
4. Investigation of the storage performance of preharvest ComCat® treated carrots and
tomatoes at different storage temperatures, being optimum refrigeration
temperatures (1°C for carrots and 13°C for tomatoes), room temperature and
evaporative cooling temperature.
5
CHAPTER2
LITERA TURE REVIEW
Abstract
The aim of this literature survey was threefold: First to explore the effect of different
preharvest treatments on postharvest quality of fruits and vegetables. Second the
principles of biological, chemical and biochemical changes in fruits and vegetables
during development, maturation, ripening and storage were reviewed. Third postharvest
handling and factors affecting quality of fruits and vegetables were examined. These
include disinfecting, packaging and storage temperature. Pre- and postharvest treatments
were found to have an effect on postharvest quality of fruit and vegetables, suggesting
that postharvest quality of produce subjected to preharvest treatments should be
assessed from a quality improvement, maintenance and consumer safety point of view.
Cold storage is one of the most important postharvest unit operations. Low-cost
alternative evaporative cooling systems are suggested as alternatives when cold storage
conditions cannot be met.
2.1. Introduction
An understanding of the changes of fruits and vegetables during storage entails more
than just knowledge of packaging methods. Preharvest as well as postharvest
physiological properties have to be understood. Therefore, in this chapter the survey on
the effect of preharvest treatments on postharvest quality of fresh commodities is
presented first. This is followed by the survey of postharvest handling and storage
including pre-packaging treatments and storage methods available for fresh
commodities. Since tomatoes and carrots were selected for this study, the survey will
mainly concentrate on these vegetables.
6
Literature Review
2.2. Development physiology of fruit and vegetables
2.2.1. Development physiology of tomatoes
Tomato physiology begins with fertilisation of the ovules of the blossom (Salunkhe
et al., 1991). Hormone production by the developing seeds and young ovary walls are
highly responsible for growth. The period from the end of flowering to and including the
ripening stage, during which chemical changes take place and new tissue is formed and
brought to morphological completion, is known as the development period (Salunkhe et
al., ' 1991). It includes stages of permutation, physiological maturation, ripening, and
senescence (Kader et al., 1985). These stages are followed by continued changes in the
chemical composition, which in turn is governed by a range of enzyme activities (Kader
et al., 1985).
Tomatoes are commercially mature at a fully developed fruit stage. Endogenous
ethylene is present in measurable quantities during the entire development of the tomato
fruit (Lyons and Pratt, 1964). It has been reported that soluble peroxidase activity
increases dramatically during the early stages of tomato fruit development, reaching a
maximum at the green mature stage (Thomas et al., 1981). The soluble peroxidase
activity remained higher during the breaker and light pink stages, but decreases in the
later stages of development (Thomas ef al., 1981). Simultaneously lAA (indoleacetic
acid) oxidase activity in the soluble fraction followed a parallel pattern to the peroxidase
activity (Frenkel, 1972, Thomas et al., 1981). Frenkel (1972) reported that the induction
of the major isozyme component of peroxidase and lAA oxidase was enhanced as the
tomato fruit ripens. The amount of auxin protectors also increased as the fruit developed
(Thomas et al., 1981).
A relationship between NADP+-malic enzyme and organic acid levels exists III
tomatoes from flowering through to ripening, and both increase during development,
reaching maximum levels at the green mature stage (Knee and Finger, 1992). However,
a decline in malate concentration is followed by a decrease in NADP-malic enzyme
activity and citrate concentration. Their data reported demonstrated that it is possible
7
Literature Review
that an enzyme is involved in cytoplasmic pH regulation. The sugar content of tomato
fruits increases progressively throughout maturation and ripening, with a pronounced
increase with the appearance of yellow pigmentation (Winsor et al., 1962a, b, in Hobson
and Davies, 1971). The starch content of tomatoes also increases with maturation,
reaching a maximum at 8 weeks after fertilisation, but is not detected in young fruit up
to 10 days. Results on the ascorbic acid content of tomatoes during the development and
ripening seemed inconsistent. However, recent studies have indicated an increase in
ascorbic acid contents of tomato fruit during maturation, with either a continuing
increase or a slight decrease during the final stages of ripening (Dalal et al., 1965,
Mohammed ef al., 1999). The malic acid concentration decreases as tomatoes ripen,
while citric acid increases up to the green-yellow stage and then generally decreases
(Hobson and Davies, 1971).
2.2.2. Development physiology of carrots
Phan ef al. (1973) gathered comprehensive information on the carrot roots during
growth up to harvest. The main constituents of carrot roots are soluble carbohydrates
comprising of non-reducing sugars, mostly sucrose, and reducing sugars, mostly
glucose. Their data showed that there was active biosynthesis of carbohydrates, mainly
sucrose, and carotenes, such as p-carotene (Phan et al., 1973). The sugars and carotene
contents of carrot roots consistently increase during the 3 months after seeding and
reach their maxima at the end of 3 months. After 3 months of the development period,
the sugar content of both groups of substances remains almost constant. The total
soluble carbohydrate concentration increases rapidly a few days after the initiation of an
entire ring of cambium in the carrot roots (Hole and McKee, 1988). Their data
concerning the relationship between enzyme activity and carbohydrates during the
development of carrot roots revealed the existence of little correlation.
The amount of organic acids and amino acids increases slowly with age during root
development and these components are present in rather low concentrations (Phan et al.,
1973). However, pyruvic acid occurs in high amounts in growing carrot roots up to 3
8
Literature Review
months, which is followed by isocitric acid and malic acid (phan et al., 1973). These
results indicated that a 3-month growth period for carrots could be sufficient before
harvest, after which there is no more increase in chemical components responsible for
good quality characteristics. However, this "biochemical maturity" is reached while
carrots are still growing in diameter and can therefore not be taken as a criterion for
determining the harvest date (phan et al., 1973).
2.3. Preharvest treatments of vegetables
2.3.1. Effect of prebarvest factors on storage quality of vegetables
Preharvest treatments of fruits and vegetables are primarily aimed at increasing
yields, while postharvest storage performance is normally neglected. Several research
results were reported on methods to increase harvest yield and qualities of fruits and
vegetables (Mitchell et al, 1997). Most research work has been targeted on cultural
practices, such as rootstock/plant age, soil management, nutrition, training and pruning
practices, crop loads, product size, and growth regulators (Rosenfeld, 1999). Bramlage
(1993) in Watkins and Pritts (1999) highlighted the almost overwhelming number of
preharvest variables that contribute to the variety of postharvest responses of the crops.
Watkins and Pritts (2001) hypothesise that the diversified postharvest responses of fruits
and vegetables during storage are in part due to preharvest cultural practice. A literature
review has shown that the major factors affecting yield and quality of vegetables are
cultivars, soil plant systems and fertiliser practices, and the environmental factors such
as temperature, relative humidity, light intensity and rainfall during production
(Rosenfield, 1999).
2.3.1.1. Soil plant system and fertiliser practice
From a literature review on the effect of cultural practice on quality of vegetables
with emphasis on tomatoes, carrots and lettuce (Rosenfeld, 1999), it was deduced that in
general, the objectives of optimal fertilisation strategy were maximization of yield, the
maximization of fruit and vegetable quality, minimization of environmental pollution
9
Literature Review
caused by fertilisers and the minimisation of fertiliser expenses. The yield of potatoes,
soybeans, cabbages, carrots, onions, cucumbers, strawberries, and eggplants oscillated
because of the different soil and climatic conditions (Data given by Polus, in Schnabl et
al., 2001). These could also suggest that there could be changes in postharvest quality
based on different soil and climatic conditions.
Postharvest quality parameters of tomatoes and carrots vary with the fertilisation
practice during production. Even under unfavourable climatic conditions, application of
phosphorous - potassium (PK) fertiliser could be used to increase carotene content in
carrots (Evers, 1989a). Photosynthetic products like sugar are slightly affected with
fertilisation (Evers, 1989a). However, Evers (1989a, b and c) showed that seasonal
variations and genetic variations are often larger than variations caused by soil and
fertiliser practices.
Qualities of carrots are reduced as a result of increased use of mineral fertiliser, but
are not affected by measure fertilisers (Lieblein, 1993) whereas increased use of
composted manure had no effect on quality of carrots. The postharvest response of
carrots is often dependent on the level of fertiliser applied during the growth period
(Petrichenko et al., 1996).
Vitamin B concentrations are higher in plants grown with organic fertilisers as
compared with plants grown with inorganic fertilisers (Mozafar, 1994). Nitrogen
fertilisers, especially at high rate, seem to decrease the concentration of vitamin C in
different fruits and vegetables, among them potatoes, tomatoes and citrus fruits
(Mozafar, 1994).
Positive and negative effects of preharvest treatments on tomatoes, either to increase
yield or improve nutritional quality, have been reported (Bialezyk et al., 1996; Gao et
al., 1996 and Carmer et al., 2001). Carmer et al. (200 I) supplied tomato plants with
either low electric conductivity (EC = 0.25 Sm") nutrient solutions or with nutrient
I
solutions supplied with 55 mM NaCI to generate at high electric conductivity (0.75m- ).
Their results showed that high electric conductivity increased the total soluble solids
10
Literature Review
(TSS) by ea. 18% and titratable acids by ea. 32% relative to low electric conductivity
treatments. The report also indicted that after storage of 2 weeks at 15oe, fruits of high
electric conductivity treated plants were 12% less firm than those of low electric
conductivity plants, and no difference in TSS or acidity were found.
Salunkhe et al (1971) has shown the effect ofTelone (1,3-dichloropropene and other
chlorinated hydropropane) and Nemagon (1,2-dibromo-3-chloropropane) on essential
nutritive components and the respiratory rates of carrots and sweet corn seeds. The
1
respiration of carrots treated with Telone and Nemagon was below 94 !-ll02 h- g-l and
1
82.8 !-ll02 h-1 g" respectively, while that of untreated carrots was 108.8 ul O2 h- g".
This result clearly showed that preharvest treatments could affect the physiology of
carrots at harvest. A significant increase in the content of total carotene, p-carotene and
total sugars, was observed, with a simultaneous decrease in respiratory rates in carrots
(Salunkhe et al., 1971). The low respiration rates indicated that the metabolic activities
of the treated carrots were low, which lead to increased shelf life without quality
deterioration. Pre-planting soil fumigation with Telone and Nemagon also resulted in
increased carotene, p-carotene and total sugars, and decreased the respiratory rates in
carrot roots (Singh et al., 1970).
Most researchers reported that there are either positive or negative effects of any type
ofpreharvest practices on quality of carrots and tomatoes, especially at harvest (Watkins
and Pritts, 2001; Tittonell et al., 2001; Ozeker et al., 2001; Sen et al. 2001). Salt
concentrations of nutrient solutions were shown to affect quality of celery more than
yield (Pardossi et al., 1999), and preharvest Ethephon (2-chloroethylphosphonic acid)
spray directly onto pepino fruits advanced colour changes (Maroto et al., 1995; Lopez et
al., 2000). Nutritional treatments had a positive effect in reducing the peel disorder of
fruits under commercial conditions (Zilkah et al., 2001). More research is needed on the
storage of fresh produce subjected to various preharvest practices. It is also
recommended that after each preharvest practice a study on the quality of vegetables and
11
Literature Review
their storability needs to be conducted in order to secure favourable storage conditions
for these products and maintain freshness and nutritional quality.
2.3.1.2. Effect of environmental factors on vegetable quality
The effect of climate on quality of vegetables is normally mostly higher than the
effect of fertiliser on photosynthetic products such as sugar (Rosenfeld, 1999).
Temperature is the major environmental factor affecting quality of vegetables.
Vegetables like carrots and tomatoes respond to various levels of temperature. Carrots
grown at high temperature were shown to have a higher total sugar content, whereas
those grown at low temperature were sweeter, specifically due to a higher sucrose
content (Rosenfeld, 1999). Apple watercore, ethylene evolution, flesh firmness,
membrane permeability and sorbitol levels were shown to be affected by preharvest fruit
temperature (Yamada and Kobayashi, 1999).
Hao and Papadopoulos (1999) have shown that supplemental lighting during growth
of cucumber increases biomass allocation to fruits, fruit dry matter content and skin
chlorophyll content. Leonardi et al. (2000) grew tomato plants in two glasshouse
compartments under two vapour pressure deficit (vpd) levels, showing that fruit growth
and transpiration rates greatly varied during daylight hours, which has enhanced under
high vpd conditions. As a result a significant reduction in fruit weight and in fruit water
content, and an increase in soluble solids was found. Environmental vapour pressure
increases can therefore affect not only growth but also quality of tomato fruits. It was
shown that air humidity has effects on growth, flowering, and finally on keeping quality
of some greenhouse species (Mortensen, 2000).
2.3.1.3. Water management
Serensen ef al. (1997) showed the effect of drought stress on carrot quality. Glucose,
fructose and sucrose concentrations in carrots exposed to drought stress at different
growth stages were not affected in any consistent manner. The results also indicated that
the concentration of dry matter was low when drought was induced at an early growth
12
Literature Review
stage in coarse and sandy soil. Averaging the effect of drought periods and cultivars,
drought stress was observed to increase the concentration of sucrose in taproots from the
coarse, sandy soil. It was also shown that drought stress increased storage losses due to
the development of disease (Serensen et al., 1997).
Research on deficit-irrigating micro-irrigated tomatoes showed that occurrence of
early blight disease (caused by the fungus Alternaria solani) was increased by 50%,
while blossom end rot incidence was five times more severe compared with full
irrigation (Obreza et al., 1996). This result indicated that deficit irrigation could cause
substantial economic loss oftomatoes through decreased crop marketable quality.
Dodds et al. (1996) studied the influence of water table depth and found that 0.6 m
depth gave the best yield and largest fruit size, however, a higher incidence of catfacing,
cracking, sunscald and loss of firmness of tomatoes were found. A balance between
yield and quality at a water table depth between 0.6 and 0.8 m was recommended for
tomato production on sandy loam soils.
On the other hand, irrigation deficit in the first growth period of tomato reduced the
number of flowers leading to a decrease in the number of fruits and in the marketable
yield (Colla et al., 1999). The soil moisture deficit resulted in increased soluble solids
and acidity of the fruit. However, reducing irrigation by 25% before fruit onset and by as
much as 50% in the fruit development and ripening stages resulted in no significant
decrease of soluble solid yield.
2.3.1.4. Hormone treatment
Hormones are essential for plant growth and development. The quality of hormone
present and tissue sensitivity to hormones has an effect on plant physiology. Plant
hormones are responsible for cell elongation, cell division, inhibition of senescence,
abscission of leaves and fruits, dormancy induction of buds and seeds, promotion of
senescence, epinasty and fruit ripening. The preharvest as well as postharvest
physiological processes in fruits and vegetables are responsible for changes in
13
Literature Review
composition and quality of these horticultural crops and depend on the plant species.
The major classes of plant hormones include auxins, gibberelins, cytokinins, abscisic
acid, brassinosteroids and ethylene (Mauseth, 1991; Raven ef al., 1992; Salisburg and
Ross, 1992; Davies, 1995).
Gibberellins are known to stimulate the physiological processes such as stem
elongation, bolting, breaking seed dormancy, enzyme production, induce maleness in
dioecious flowers, cause parthenocarpic (seedless) fruit development and can delay
senescence in leaves and citrus fruits (Mauseth, 1991; Raven ef al., 1992; Salisburg and
Ross, 1992; Davies, 1995). Cytokinin stimulates cell division, morphogenesis in tissue,
the growth of lateral buds, release of apical dominance, leaf expansion resulting from
cell enlargement, enhances stomatal opening in some species and promotes the
conversion of etioplasts into chloroplasts via stimulation of chlorophyll synthesis
(Mauseth, 1991; Raven et al., 1992; Salisburg and Ross, 1992; Davies, 1995). The
functions of abscisic acid are to stimulate the closure of stomata, inhibition of shoot
growth, induction of seeds to synthesise storage proteins, induction of _gene
transcription, especially for proteinase inhibitors in response to wounding, which may
explain an apparent role in pathogen defence (Mauseth, 1991; Raven et al., 1992;
Salisburg and Ross, 1992; Davies, 1995). Ethylene has been the most studied plant
hormone in relation to fruit ripening and postharvest storage. Some of the functions of
ethylene are to stimulate the release of dormancy, shoot and root growth, and
differentiation of adventitious root formation, leaf and fruit abscission, bromiliad flower
induction, induction of femaleness in dioecious flowers, flower opening, flower and leaf
senescence and fruit ripening (Mauseth, 1991; Raven et al., 1992; Salisburg and Ross,
1992; Davies, 1995).
The other growth regulating compounds are brassinosteroids, salicylates, jasmonates
and polyarnines. An abundance of research has been devoted on the chemistry and
physiology of natural growth regulators resulting in the recognition of brassinosteroids
as a new class of phytohormones (Sasse, 1997; Schnabl et al., 2001). Some of the
14
Literature Review
effects of brassinosteroids include stimulation of stem elongation, inhibition of root
growth and development and promotion of ethylene biosynthesis and epinasty. Recently,
the brassinosteroids has gained a broad spectrum of application and extremely low
toxicity and mutagenicity have received increasing attention (Schnabl et aI., 2001).
Previous work showed that brassinosteroids are plant growth promoting regulators,
which are effective in cell elongation and division, source/sink metabolism, chlorophyll
synthesis and reproductive and vascular development (Clouse, 1996; Mandalla, 1988).
Sasse et al. (1995) and Takatsuto et al. (1996) reported that they enhance nutrient
contents, improve shape and taste of fruits, have beneficial effects on germination,
growth and seed quality. Much research has been conducted on the potential
performance and investigations of the potential applications of brassinosteroids in
agriculture (Schnabl et al., 2001). This will be elaborated upon section 2.3.1.5 below.
2.3.1.5. Communication Catalization (ComCat®) treatment
Recently, a hormone containing treatment has been introduced as an alternative
agricultural input to the use of chemicals to increase production of vegetables and other
crops. ComCat® is a natural biocatalyst, which is extracted from seeds of plants and
mainly consists of amino acids, gibberellin, kitenins, auxin (indole-3-acitic acid),
brassinosteroids, natural metabolites, pathogen-related PR-proteins with defence
reactions, terpenoids, flavonoids, vitamins, inhibitors, other signal molecules,
biocatalysts and cofactors. The yields of ComCat® treated vegetables were shown to be
increased for cabbage (8%), tomato (16-19%), potato (9-19%), soybeans (26-30%),
eggplants (37%), cucumbers (25-32%), carrots (32%), onions (49%) and strawberries
(50%), compared to control vegetables and fruits (Schnabl et al., 2001). These
vegetables were also shown to have better root development, improved resistance
induction, less chance of deficiencies with fertiliser, higher resistance to pathogens prior
to harvest and they seem to have a slightly better resistance to environmental stress, and
increased protein content (Hiister, 2001; Schnabl et al., 2001).
15
Literature Review
A reduction of plant disease symptoms of up to 45% in comparison to untreated
control plants has been found. This is the result of induction of the PR-proteins
(pathogenesis-related proteins) namely peroxidase, chitinase and 1-3 gluconase. These
enzymes protect cell walls and prevent infection by fungi (Huster, 2001). Advantages of
ComCat® treatment are that only low doses are necessary to show measurable effects of
these brassinosteroids containing plant extract in crop plants, their environmental safety
and the possibility of reducing the amount of pesticides needed (Schnabl et al., 2001).
Apart from studies on yield increase, no data is yet available on the effect of preharvest
ComCat® treatment on quality of fruits and vegetables at harvest, as well as during
storage. ComCat® was approved by, and registered with the Federal German Biological
Centre of Agriculture and Forestry (BBA), Institute for Integrated Plant protection, as a
harmless plant strengthening substance of plant origin. It is also licensed for use in
Ecological Farming, according to the EU-regulation 2092/91.
As discussed, the effects of ComCat® include (a) serving the plant as a general
strengthening agent for the organic development, (b) inducing resistance through
activating plant own defence mechanisms against pathogens, and biotic and abiotical
stress factors, (c) improve root development, (d) increase yield in agricultural cash crops
as well as horticultural crops and (e) increase protein content.
2.4. Postharvest physiology of fruit and vegetables
2.4.1. Respiration
Respiration is defined as a process by which stored organic materials (carbohydrates,
proteins, and fats) are broken down into simple end products with a release of energy. In
the process 02 is used and C02 is liberated. Vegetables continue to respire after harvest
and during storage. Each type of vegetable and cultivars requires a specific range of CO2
and O2 concentration levels for safe storage without the occurrence of physiological
disorder. The level of physiological activity and potential storage life can be indexed by
the rate of respiration. Respiration is one of the basic physiological factors, which
16
Literature Review
speeds up ripening of fresh commodities and is directly related to maturation, handling,
and ultimately to the shelf life (Ryall and Lipton, 1979; Ryall and Pentzer, 1982).
Generally, the loss of freshness of perishable commodities depends on the rate of
respiration. An increase in respiration rate hastens senescence, reduces food value for
consumers, and increases the loss of flavour and sellable dry weight.
Stored intact fruits and vegetables face desiccation and chilling injury after harvest
and during storage. Due to wounding stress, as a result of chilling or mechanical
injuries, respiration rate and overall metabolic activities usually increase. The main
physiological manifestation of metabolic activities include increased respiration rate
and, in some cases, ethylene production (Rosen and Kader, 1989).
The index of physiological activity and potential shelf life have a direct relationship
with respiration of fruits and vegetables. Since sugars in fruits and vegetables play a role
in the respiration process, the quantity of sugars in fruits and vegetables available for
respiration is the dominant factor for the shelf life of these commodities at a given
temperature (Paez and Hultin, 1972). For normal respiration, removal of respiratory C02
needs more emphasis than supply of O2, because some fruits and vegetables are highly
sensitive and could be suffocated with a high level of C02 (Duckworth, 1966; Kader et
al., 1985). Removal of respiratory heat requires attention because it increases the
product temperature and surrounding air temperature, which in turn is responsible for
increasing respiration and causes acceleration of substrate utilization, predominantly
sugars (Ryall and Lipton, 1979; Ryall and Pentzer, 1982). The rate of respiration
depends on the quantity of available O2 as well as the storage temperature. A decrease in
rate of respiration increases the shelf life of fruits and vegetables. In order to achieve
long storage life of fruits and vegetables, the rate of respiration should be reduced
through decreasing the 02 level, slightly increasing the CO2 level, and decreasing the
storage temperature, which includes removal of respiratory heat (Duckworth, 1966;
Kader et al., 1985). The optimum gas composition is the range of O2 and CO2 levels
that would minimise physiological disorder, reduce respiration rate and reduce ethylene
17
Literature Review
production during storage. The limit of tolerance to low O2 and high CO2 levels depends
on several parameters including temperature, physiological conditions, maturity, and
previous treatment.
2.4.2. Temperature quotient of respiration
Temperature highly affects the metabolic activities of fruits and vegetables.
Relatively higher temperatures increase the rate of respiration and ethylene production
during storage. The rate of chemical reactions in fruits and vegetables is also controlled
by temperature. Itwas reported that theoretically, the rate of respiration doubles for each
10°C increase in temperature. Depending on the maturity and anatomical structure of the
fruits or vegetables, the temperature quotient of respiration may be more than double
(Ryall an Lipton, 1979; Ryall and Pentzer, 1982; Sargent et al., 1991). These researchers
showed that the respiration rate of topped carrots increased by 79% at 25 - 27°C, when
compared to topped carrots at O°C. Similarly, the rate of respiration (rate of CO2) of
bunched carrots increased by about 71% at 25 - 27°C, compared to those at O°C
(Hardenburg ef al., 1986), and the respiration rate of mature green tomatoes increased
by 100% when stored at 25 - 27°C compared to storage at O°C (Hardenburg ef al.,
1986).
Preharvest treatments on a farm, or in an orchard, affects postharvest physiology of
fruits and vegetables, such as the respiration rates. Physiology of fruits and vegetables
begins at the time of blossoming or bud formation and is affected by preharvest factors
such as fertilisation, variety, and irrigation, and by environmental factors such as
sunlight duration and quality, temperature, humidity etc., as well as preharvest spray of
hormones and growth regulators (Ryall and Lipton, 1979; Ryall and Pentzer, 1982;
Schnabl ef aI., 2001). These were reviewed in section 2.3 above. These treatments could
possibly have positive or negative effects on the postharvest quality and shelf life of
fruits and vegetables, indicating the importance of further integrated research on pre-and
postharvest physiology when implementing new preharvest treatment agents or
methods.
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Literature Review
2.4.3. Ethylene production and effects
Ethylene advances the onset of an irreversible rise in respiration rate in climacteric
fruit and increases the ripening process. The effect of low O2 and high C02 levels on the
production of ethylene adds to the nature of the ethylene production or inhibition
process. Fruits and vegetables are classified into five groups according to ethylene
production rates within the ranges of 0.1 ml ethylene kg-lh-I at 20°C to 100.0 ml
ethylene kg" h-I at the same temperature (Kader ef al., 1985). In general, the ethylene
production rates of tomatoes range from 1.0 - 10 ml kg-lh-I at 20°C, which classifies
them in the moderate class according to ethylene production rate (Ryall and Lipton,
1979; Kader et al., 1985). Tomato is one of the few vegetables to which a known
phytohormone, ethylene, is applied commercially to influence the rate of ripening.
Ethylene plays a significant role in the physiological and biochemical changes that occur
with the climacteric onset. Lyons and Pratt (1964) reported that endogenous ethylene
was present in measurable quantities during the entire growth phase of the tomato fruit.
The concentration of ethylene increased IO-fold when fruit growth reached 70-93% of
its total fruit growth (Lyons and Pratt, 1964). It was also shown that the concentration of
ethylene increased 400 times that of the average measured during growth, at the
climacteric onset of ethylene production and onset of ripening. External introduction of
ethylene to tomatoes at all stages of development induces ripening and climacteric onset
along with phenotypic changes common to normal ripening, such as red color
development, fruit softening, and characteristic flavour (McGlasson, 1978 and 1985).
However, the acceptable edible quality of tomatoes can only be attained with those that
were 93% mature (McGlasson, 1978 and 1985).
In shelf life improvement, maintaining low ethylene concentration and reducing
ethylene biosynthesis plays a significant role. Adams and Yang (1979) have shown that
aminoethoxyvinylglycine (AVG) block the conversion of s-adenosyl-methionine to 1-
aminocyclopropane-l-carboxylic acid. Aminoethoxyvinylglycine was also effective in
inhibiting ethylene synthesis in slices of green tomatoes, but was only relatively
19
Literature Review
effective in pink and red tomato fruits. Low temperature also reduces induction of
ethylene in tomato fruits during storage, so that the shelf life of tomatoes is increased,
when stored at low temperature. Higher temperatures increase ethylene production and
result in advanced physiological and biochemical changes in fruit (Wiley, 1994).
Ethylene-induced formation of isocoumarin was also characterised in relation to
ethylene-enhanced respiration in whole or cut carrots (Lafuente et al., 1996). Sarker and
Phan (1979) reported that ethylene induces the formation of isocoumarin (8-hydroxy- 3-
methyl-6-methoxy-3,4-dihydro-isocomarin) in carrots, a compound associated with
bitterness in carrots (Carlton et al., 1961; Simon, 1985). Concentrations of ethylene
ranging from 0.1 to 5 ppm, and temperatures from 1 to 15°C, increased respiration,
resulting in a more rapid formation of isocoumarin (Lafuente et al., 1996). It was also
shown that exposure to low levels of ethylene (0.5 ppm) for 14 days at 1 or 5°C resulted
in isocoumarin contents of 20 and 40 mg/l00g peel, respectively. These levels were
sufficient to bring a detectable bitter flavour in intact carrot roots. These results clearly
indicated that carrot quality is highly sensitive to ethylene during storage and
transportation, suggesting that ethylene concentration as well as its biosynthesis should
be controlled during commercial storage of carrots.
The presence of the commonly identified phytohormones and varIOUS growth
regulators are believed to have an inductive effect on ethylene production of fruits and
vegetables during ripening (Abdel-Rahman et al., 1975; Davey and Van Staden, 1978;
Ryall and Lipton, 1979; Ryall and Pentzer, 1982). Some chemicals applied to bring
about abscission of fruits and vegetables that are important in fruit thinning and
mechanical harvesting have been shown to induce ethylene production. These can cause
premature ripening in fruits and bitterness in carrots.
2.4.4. Transpirationalloss
Storage temperature and relative humidity play an important role in the physiological
changes of fresh produce including physiological weight loss. Water loss is rapid at low
relative humidity, since the vapour pressure difference between the commodity and
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Literature Review
surrounding air is a driving force for moisture transfer from the wet product to the air. In
most of the cases moisture content of fresh fruits and vegetables are very high (usually
greater than 70%). Therefore, the air inside the flesh is nearly saturated i.e. close to
100% relative humidity. Berg and Lentz (1966) noted that the lower humidity ratio
causes desiccation and marked softening of carrots, together with some increase in
decay. High relative humidity is therefore desirable for reducing physiological weight
loss during storage of fruits and vegetables.
Temperature is the other major environmental factor that considerably affects the
postharvest physiological weight loss of stored vegetables (Salunkhe et al., 1991). The
commodity temperature is highly dependent on the surrounding air temperature. Usually
weight loss from perishable commodities is high if surrounding air temperature, flesh
moisture content and temperature are high. Vapour pressure increases as air, flesh
temperature and moisture content increases. Depending on the magnitude of temperature
gradients and relative humidity of the surrounding air the physiological moisture loss
. varies. In summary, the most important ways to reduce physiological weight loss are by
increasing relative humidity and decreasing storage temperature.
2.4.5. Postharvest physiological disorder
Postharvest physiological disorders affect mainly fruits. Susceptibility to disorders
was shown to be dependent on a number of factors, such as maturity at harvest, cultural
practices, climate during the growth season, produce size, harvesting, and handling
practices. Adverse environmental conditions or a nutritional deficiency during growth
and development of fruits and vegetables cause post harvest physiological disorders
(Brown, 1973; Eckert et al., 1975; Eckert, 1978a, b and c). They may be classified as
low temperature disorders, postharvest physiological disorders and mineral deficiency
disorders. Low temperature storage is beneficial because it reduces respiration and
metabolic activities. Tropical and subtropical fruit and vegetables require specific ranges
of storage temperature. On the other hand, low temperature does not reduce all aspects
of metabolism to the same extent as it reduces respiration. This could lead to a
21
Literature Review
metabolic imbalance due to an accumulation of reaction by-products and possibly a
shortage of substrates. Chilling injury is a disorder long observed in plant tissues,
especially those of tropical or subtropical origin. This injury is due to the exposure of
plant tissue to temperatures below their critical temperature, which is usually below
15°C (Ryall and Lipton, 1979; Bramlage, 1982; Couey, 1982; Wills et al., 1989). The
physical symptom of chilling injury and the lowest safe storage temperature for some
fruits and vegetables varies. Pitting of the skin due to the collapse of cell beneath the
surface and browning of flesh tissues are some of the common symptoms of chilling
injury. Therefore, selection of a proper storage temperature range for fruits and
vegetables is a critically important factor in order to maintain the best quality and
increase shelf life. The approximate lowest safe storage temperature for tomato fruit
varies between 7.2-12.8°C (Hardenburg et al., 1986), while carrot roots are not
susceptible to chilling injury when stored at temperatures as low as O°C.
2.4.6. Chemical and biochemical changes during ripening and storage
During ripening of fruits, several biodegradation processes take place, such as
depolymerization, substrate utilization, loss of chloroplasts, and pigment distraction,
mainly due to the action of hydrolytic enzymes (esterases, dehydrogenases, oxidases,
phosphatases and ribonucleases) (Baker, 1975; Mattoo et aI., 1975). There are also some
biosyntheses associated with these processes such as syntheses of proteins and nucleic
acids, maintenance of mitochondria, oxidative phosphorylation, phosphate ester
formation and syntheses linked to the metabolic path way (Baker, 1975; Mattoo et al.,
1975).
2.4.6.1. Carbohydrates
Among the changes that may occur ~uring ripening of flesh fruits, such as tomatoes,
is a change in the carbohydrates composition mainly due to substrate .utilization and
action of hydrolytic enzymes (Pratt, 1975). The presence of free or combined sugars
with other constituents plays an important role in flavours of vegetables through a sugar
to acid ratio balance. During ripening of fruit, carbohydrates undergo metabolic
22
Literature Review
transformations, both qualitatively and quantitatively. Starch is completely hydrolysed
into glucose, and fructose and sucrose formed as ripening progresses (Mattoo et al.,
1975). However, structural carbohydrates are decreased slightly. Mattoo et a/. (1975)
reported that pentosans and cellulose are stored carbohydrates, which may also serve as
potential sources of acids, sugars, and other respiratory substances during ripening.
In tomatoes natural sugars such as arabinose, rhamnose, and galactose are steadily
decreased in cell walls as the color changes (Campbell et al., 1990). Several studies
have also shown that changes in cell wall carbohydrates similar to those reported for
intact fruits occurred in cell walls from pericarp discs (model for intact tomato fruits)
(Gross and Wallner, 1979; Gross, 1984; Campbell et al., 1990). Other studies showed
that the total sugar content of tomatoes increased during ripening, and may be followed
by no further changes or a slight decrease during ripening (Baldwin et al., 1991).
Similar findings were reported by other researchers, who showed that sucrose content in
tomatoes also decreased with the progress of ripening (Goodenough et a/., 1982;
Baldwin et al., 1991).
During storage of fruit and vegetables, free sugars show a general initial increase
followed by a decrease. The increase in free sugars in some fruit and vegetables are due
to the breakdown of polysaccharides. In some fruits approximately equal quantities of
glucose and fructose are formed due to hydrolysis of starch. However, as storage time
advances, especially in fruit, the content of all three free sugars (sucrose, glucose and
fructose) declines. Several factors contribute towards the excessive decline of sugars
during storage, such as fruit maturity, storage temperature, concentration of 02, N2,
ethylene and CO2• Higher temperature favours faster utilisation of sugars as substrate in
the respiration process (Wiley, 1994).
In carrots, the ratio of nonreducing to reducing sugars exhibits a sharp decrease after
14 to 18 weeks of storage at 1.1°C. Simultaneously an active synthesis of reducing
oligosaccharides as raffinose together with the formation of new rootlets is observed
(Phan et al., 1973). Temperature also regulates the rate at which biochemical changes
23
Literature Review
occur during storage. Higher temperature activates enzymatic catalysis and leads to
chemical and biochemical breakdown of chemicals in fruits and vegetables during
storage. As a result, fruits and vegetables loose fumness faster at higher temperature due
to high enzymatic activities (Yoshida et al., 1984).
2.4.6.2. Organic acids
Common acids found 10 fruit includes citric, malic and ascorbic acid. During
ripening, organic acids are among the major cellular constituents undergoing changes
(Salunkhe et al., 1991). Studies have shown that there is a considerable decrease in
organic acid during ripening of fruits. Modi and Reddy (1966), in Salunkhe et al.
(1991), showed that concentrations of citric, malic and ascorbic acids declined 10, 40
and 2.5 fold respectively, in fruits such as tomatoes. The titratabie acidity decreases with
storage time, especially at higher temperatures (Mohammed et al., 1999). Higher storage
temperatures are known to have an increasing effect on the rate of decrease in ascorbic
acid content in tomatoes during storage (Salunkhe et al, 1991). However, Mohammed et
al. (1999) showed that the ascorbic acid content in tomatoes slightly increased during
ripening during storage at 20°C for 14 and 21 days. In general, the ascorbic acid content
decreases rapidly after full ripening of tomatoes stored at higher storage temperatures.
In carrots, titratabie organic acidity decreases slowly during storage (Phan et al.,
1973). However, Phan et al. (1973) reported that stored carrots had high contents of iso-
citric and malic acids, which they could not explain. Pyruvic and oxaloacetic acids were
not detected in these stored carrots.
2.4.6.3. Enzyme activity
As was mentioned above, the biochemical changes are responsible for development
of off-flavours, discoloration and loss of firmness of fruit and vegetables and are
affected by enzymes. The most important enzymes related, to food quality include
lipolytic acyl hydrolase, lipoxygenase, peroxidase, catalase, protease, polyphenol
oxidase, amylase, pectin methylesterase, polygalacturonase, ascorbic acid oxidase and
24
Literature Review
thiaminase (Svensson, 1977). Lipolytic acyl hydrolase, lipoxygenase, peroxidase,
catalase and protease are responsible for the changes in flavour of minimally processed
as well as intact fruits and vegetables, while polyphenol oxidase is responsible for the
changes in colour, especially during ripening of fruits and vegetables (Wiley, 1994). The
changes in softness of fruits and vegetables are due to the activities of amylase, pectin
methylesterase and polygalacturonase, which result in loss of texture. The reaction
catalysed by ascorbic acid oxidase and thiaminase leads to the loss of nutritional quality
offood in terms of vitamins C and B content (Wiley, 1994). Catalase and peroxidase are
also known for their oxidative activity during ripening and their activity levels increases
considerably during ripening of fruit and vegetables (Mattoo et al., 1975). Glycolytic
enzymes are groups of enzymes responsible for the glycolytic breakdown of sugars, and
they increase considerably during ripening of fruits. Other classes of enzymes active
during storage of fruit and vegetables include hydrolytic enzymes, invertase,
transminases, citrate cleavage enzymes, enzymes of the tricarboxylic acid cycle and
chlorophyllase (Mattoo et aI., 1975), which are responsible for the hydrolysis of starch,
flesh softening in most fruits, the degradation of sucrose, liberation of monosaccharides,
turnover of amino acids, and ensuing chlorophyll degradation during ripening.
El-Zoghbi (1994) reported effects of enzyme activity on alcohol-insoluble solid
dietary fibres, and texture and firmness changes during ripening of tropical fruit such as
mango, guava, date and strawberry. The results showed that alcohol-insoluble solid,
dietary fibres, texture and firmness declined in these fruit during ripening. However,
both polygalacturonase as well as cellulase activities of the fruits increased markedly,
during ripening.
The pectin-degrading polygalacturonase (PG) isoenzymes are highly responsible for
softening of fruit (Hobson, 1964; Tigehelaar et al., 1978; Marangoni et al., 1995).
Bruinsma et al. (1990) demonstrated that these enzymes are highly responsible for most
chemical and biochemical changes associated with deterioration of fruit and vegetable
quality during ripening and storage. Postharvest treatment had also an effect on
25
Literature Review
biochemical changes related to enzymatic activities during storage (Marangoni et aI.,
1995; Yoshida et al., 1984; Dodds et aI., 1996; Assi et aI., 1997). PG normally
accumulates to high levels in ripe tomatoes (Kramer et aI., 1992). Similarly, Brummell
and Harpster (2001) reported that polygalacturonase activity is largely responsible for
pectin depolymerization and solublization of polysaccharides. The loss of firmness of
tomatoes during ripening is due to the increased activities of PG and pectin esterase (El-
Zoghbi, 1994). In tomato it was shown that ethylene production was induced prior to
polygalacturonase production and that it is responsible for triggering PG synthesis
indirectly (Grierson and Tucker, 1983). Extracted PG activity in non-chilled tomato fruit
significantly correlated with softening of the fruit. However, chilling-associated
softening correlated with higher initial extracted pectinmethylesterase (PME) activity. It
was suggested that loss of turgor from translocation of water to the PME-modified cell
walls was responsible for loss in firmness as a consequence of chilling. Heat treatment,
on the other hand, strongly reduces PG activity of tomatoes during ripening and storage
(Yoshida et al., 1984). In general, relatively higher temperatures (about 22°C) favour
development of PG activity in tomatoes and high temperature treatment suppresses this
enzyme activity (Yoshida et aI., 1984).
Biochemical processes are also responsible for colouration and loss of firmness of
fruits and vegetables (Kertesz, 1951; Doesburg, 1965; Hildebrand, 1989). As a result of
increased enzymatic activity occurring due to storage temperature, postharvest quality of
tomatoes such as red colour formation, firmness, titratabie acidity and decay during
ripening are affected (Batu, 1998). Changes in colour from green to red are delayed in
the case of tomatoes stored at lower temperature as compared with relatively higher
temperature, since the lower storage temperature reduces enzymatic activity. This could
lead to increased acidity during storage.
2.4.7. Postharvest microbiology of fruit and vegetables
The freshness quality and consumer safety of fruits and vegetables depend on the
microbial population at harvest, as well as during storage (Brackett, 1992). Fruit and
26
Literature Review
vegetables are highly susceptible to microbial contamination during growth, harvest and
postharvest operations (Madden, 1992). Most fruits have pH values below 4.5.
Consequently, under such acidic conditions most of the microorganisms cannot grow
easily. Conversely, most vegetables have pH's above 4.5, which creates favourable
conditions for various types of microorganisms. Carrots have pH values varying from
4.9-6.3 while tomatoes have lower pH values ranging between 3.9 and 4.7 (Banwart,
1989). Microorganisms account for up to 15% of postharvest decay of fruits and
vegetables. Bacteria, yeast and moulds are the three important groups of
microorganisms that affect the quality of fruits and vegetables during storage. The
sources of these microorganisms could be from environmental air, soil, and poor
sanitation during postharvest unit operations.
Several distinct mechanisms for preharvest infection are known. Lesions on stems,
leaves and flower parts of infected plants as well as dead plant materials are sites for
sporulation of pathogenic fungi (Nelsen, 1965; Salunkhe et al., 1991). Rain and wind
transport spores of these fungi to flowers and fruits at every stage of their development.
When free water is present and the climatic conditions favourable, these spores
germinate and rapidly increase the microbial population. The population and type of
microorganisms associated with fruit vegetables are different from those of stem and
root vegetables, the reason being the differences in chemical composition such as
moisture content, titratable organic acid, and free sugar content. Usually the microbial
population is higher on stem and root vegetables than in most fruits mainly due to
acidity and may be due to the contact with soil. The most important postharvest diseases
of tomatoes include alternaria, rhizopus, buckeye, grey mold, soft rot, acid rot, bacterial
soft and ripe rot, which are caused by Alternaria alternata, Phytophthora species,
Botrytis cinerea, Rhizopus stolonifer, Alternaria tenuis, Geotrichum candidum, Erwinia
cartovora or Pseudomonas species and Colletotrichum species, respectively (Senter et
al., 1987; Splittstoesser, 1987; Buick and Damoglou, 1987; Brackett 1988a; Bulgarelli
and Brackett, 1991; Salunkhe et al 1991). The major postharvest diseases of fresh
27
Literature Review
carrots are gray moulds rot, centrospora rot, watery soft rot and bacterial soft rot which
is due to Botrytis cinerea, Centtrospora acerina, Sclerotinia sclerotiorium and Erwinia
cartovora, respectively. Similarly, losses of other vegetables in general are due to
watery soft rot, cottony leak., fusarium rot, and bacterial soft rot that are caused by
Sclerotinia, Pythium butleri, Fusarium and Erwinia or Pseudomonas species,
respectively.
As ripening of fruits and vegetables progresses, the firmness decreases and the
intrinsic factors, which confer resistance during development, can no longer protect
against microbial decay (Eckert et al., 1975 and 1978). The high moisture and nutrient
content of fruits and vegetables adds to susceptibility to invasion by specific pathogenic
microorganisms (Eckert, 1978 a, b and c).
The microbial deterioration of fruits and vegetables are highly influenced by
environmental factors, such as temperature, moisture content of crops, relative humidity
of air, and storage air gas composition. In general, control of postharvest decay of fruits
and vegetables are based upon the prevention of infection before as well as after harvest,
eradication of incipient infections and retarding the progress of the pathogen in the host
by postharvest treatments such as disinfection (Eckert et al., 1975).
2.5. Post-harvest handling and storage
2.5.1. Pre-packaging treatments
2.5.1.1. Postharvest disease control
As mentioned above, the postharvest quality and safety of fresh fruits and vegetables
mainly depends on their microbial population (Brackett, 1992). Different approaches
have been used to reduce postharvest loss, classified in chemical and non-chemical
methods. Various synthetic fungicides and bactericides have been used alone or in
combination with chlorination to limit the growth and transmission of diseases caused
by microorganisms during storage of fresh commodities. However, chemicals may have
a negative impact on agriculture in developing countries (Eckert, 1990; Conway et al.,
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Literature Review
1999; Qadir and Hashinaga, 2001). Biological products such as Aspire, BioSave, and
Yield Plus are now available in the marketplace of developed countries to control
growth of bacteria or fungi. Pseudomonas syringae van Hall (strain ESC-ll) is sold
commercially under the names BioSave-ll and BioSave-l10 (EcoScience Corp.,
Orlando, Florida), and is currently being used to control decay on apples and pears
caused by Botrytis cinerea, Mucorpiriformis fischer, and Pseudomonas expansum
(Janisiewicz and Marchi, 1992; Janisiewicz and Jeffers, 1997).
Other methods used to control postharvest diseases are modification of pH, chemical
treatments or a combination (Huxsoll and Bolin 1989; King and Bolin, 1989). The
success of these products, however, remains limited (Wisniewski et al., 2001). The
reason may include the following: (a) there is an increasing consumer concern over the
use of pesticide as a postharvest decay control of food (Wisniewski and Wilson, 1992),
(b) the use of fungicides may result in predominance of fungicide resistant strains
(Elmer and Gaunt, 1994), (c) the variability experienced in the efficiency of these
products, and lack of understanding of how to adapt "biological approaches" to a
commercial setting (Wisniewski et al., 2001). Researchers and industries have come up
with some noble ideas such as using combinations of different antagonists. However,
these approaches seem to meet with consumer resistance (Wisniewski et al., 2001).
Much work as been done on non-chemical approaches and efficient postharvest
disease control methods including various physical treatments such as biocontrol agents,
heat, ultra-violet light and ionising radiation. Some novel heat treatment approaches to
postharvest decay control of fruits and vegetables were developed and applied in Israel
(Rodov et al., 1995; Afeke et al., 1998; Fallik et al. 1999, Fallik et al., 2000). The
postharvest decay of bell pepper was significantly decreased by hot water treatment
dipping at temperatures of 45 and 53°C for 15 and 4 minutes, respectively (Gonzalez et
al., 1999). Heat treatment, when combined with fungicide treatments, was also reported
to be effective and can be a useful alternative method to control postharvest decay
(Conway et al., 1999). In this case the effect of fungicide residues on human health and
29
Literature Review
costs associated with combinations of treatments has to be considered. However, the
application of some of these methods, such as heat treatment, requires equipment that is
complex and costly for use in under-developed countries (Rodov et al., 1996).
Intensive research was conducted on the efficiency of chlorine solutions to control
the growth of pathogenic microorganisms on fresh produce and minimally processed
"ready-to-eat" fruits and vegetables (Wei et al., 1995; Zhuang et aI., 1995; Park et al.,
1995; Velazques et al., 1998, Beuchat et al., 1998; Delaguis et al., 1999; Escudere et
al., 1999; Li et al., 2001; Beuchat et al., 2001; Ukuku and Sapers, 2001; Cantwell et al.,
2001; Prusky et al, 2001). These studies were carried out on the survival of inoculated
spoilage fungi such as Alternaria hydrophila (Velazquez et al., 1998; Beuchat et al.,
2001), Alternaria alternata (Prusky et al. 2001) and human pathogenic bacteria such as
Salmonella montevideo (Zhuang et al., 1995), Salmonella stanley (Ukuku and Sapers,
2001) and Yersinia enteroocolitica (Escudero et al., 1999). Similarly, studies on the
normal microbial populations of harvested vegetables were also reported (Beuchat et
al., 1998; Prusky et al. 2001). The concentration of free chlorine in these studies varied
from 50-2000 and ppm and dipping times from 1-10 minutes.
Chlorination, when used in combination with non-chemical methods, is effective in
reducing postharvest disease losses. Warm chlorinated water was shown to reduce
microbial loads by 3 log cfu. g' in lettuce washed in chlorinated water at 47°C, and 1
log cfu. g-l at 4°C (Delaquis et al., 1999). Similarly, the combination of different
chlorine concentrations (50 to 400 mg/ml NaOCl, pH 7.0) with 52.5°C water were
shown to be more effective than use of water or chlorine solutions at 20°C for reducing
initial microbiological flora in minimally processed green onions (Cantwell et aI.,
2001). Park et al. (1995) reported that the microbial load of the minimally processed
watercress and onion was effectively reduced with chlorine (100 ppm). However, high
concentrations of chlorine resulted in greater microbial proliferation after 7 days of
storage, loss of ascorbic acid and significant colour changes in stored cut vegetables.
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Literature Review
Preharvest dipping treatment in the organic chlorine compound Troclosene Sodium
extended the storage life of fruit by delaying development of black-spot disease (Prusky
et al., 2001). All the research work cited here, has been devoted to the control of
pathogens and postharvest decay by microorganisms without any emphasis on the effect
of free chlorine on the quality, or the physiological and biochemical quality changes.
In general, chlorination is an effective method especially in reducing microbial load
in intact fruits and vegetables. For several reasons, such as availability of chlorinated
solutions and cost, chlorine disinfection seems to be a good method for application in
developing countries. The efficacy of chlorine solution on postharvest physiological as
well as chemical and biochemical changes still needs to be explored.
2.5.1.2. Electrochemically activated water (anolyte water)
Anolyte water is prepared from an aqueous solution of NaCI and this
electrochemically-activated water is known to be a powerful, non-toxic, non-hazardous
disinfectant. Two kinds of electrochemically activated water are produced, anolyte and
catholyte. The anolyte water is described as having an oxidation-reduction potential
(ORP) in the region of +1000 mV and catholyte an ORP of -800 mV, and the pH value
of catholyte is in the alkaline region while the pH value of anolyte is in the acidic
region. Current thinking around the concept is that the ORP of both solutions fluctuates
between these values at a rate too rapid to measure. Some of the biocidal agents (free
radicals) in the solutions are CI02, HCIO, Ch, ClO-, H202, H02-, NaHO, O2, 03, H· and
·OH. Prilutski and Bakhir (1997) investigated properties of anolyte and catholyte
produced by diaphragm electrolysis of aqueous solutions. Their results showed that
catholyte and anolyte have different physical-chemical properties. Anolyte is thought to
have the antimicrobial effect and catholyte a detergent or cleaning effect (Popova et al.,
1999). The presence of the free radicals with their oxidising effects in the solutions is
considered of great importance. It is the free radicals (working substances), which gives
anolyte bactericidal and sporicidal activity (Aquastel, 2000), since higher organisms
possess antioxidant defence systems, whereas microorganisms generally do not.
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Literature Review
The electrochemically produced anolyte water was effectively used in drinking water
disinfecting units (Aquastel, 2000). The determination of organic chlorine compounds
and trihalogenmethanes showed significantly less formation of these by-products.
Moreover, the formation of halogens was significantly less than defined standard
requirements and the pH-value only slightly decreased (Aquastel, 2000). Anolyte
attracts interest since it is an environmentally and ecologically friendly substance for use
as a postharvest fruit and vegetables disinfectant. Based on these and the antimicrobial
action of anolyte, its potential to be used as a postharvest disinfectant of fruit and
vegetables should be explored.
2.5.2. Packaging
2.5.2.1. Controlled atmosphere packaging
Controlled atmosphere storage refers to storage of food in a gas atmosphere that is
different from the normal composition of air. In controlled atmosphere the headspace
gas is precisely adjusted to the atmosphere composition required by a specific fruit or
vegetable (Perry, 1993). Controlled atmosphere storage is mostly used for the long-term
storage of whole fruits and vegetables in warehouses, bulk storage and transportation.
Over 4000 research papers have been published giving information on the optimal
modified atmosphere conditions for cultivars of fruits and vegetables (Zagory and
Kader, 1988; Kader et al., 1989). These literatures have built good basic principles of
controlled atmosphere storage and significantly contributed towards the success of this
technology in developing countries (Lioutas, 1988).
The major influence on the choice of controlled atmosphere conditions is the
susceptibility of particular cultivars to superficial scald (Johnson, 1999). Using
controlled atmosphere storage methods, the gas compositions have to be adjusted to a
certain level specific to each fruit and vegetable type, and it is unlikely that there will be
benefits from further adjustment of the compositions of oxygen and carbon dioxide
without risking the damage to certain fruits and vegetables (Johnson, 1999).
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Literature Review
The controlled atmosphere gas compositions required by a given commodity is
obtained by mixing appropriate volumes of gases. Certain machinery is needed to mix
and control the gas composition of the air during the storage period. In controlled-
atmosphere storage packaging, atmospheric conditions (level of gases) are continuously
controlled and adjusted to maintain the optimal concentrations required by specific fresh
produce. As a result of this, it is capital intensive and expensive to operate for short-
term storage (Kader et al., 1989). The factors that could probably determine the success
of controlled atmosphere technology in developing countries are the cost and
complexity (multi disciplinary nature) of the technology. However, controlled
atmosphere storage is not appropriate for some commodities. For example, Lipton
(1977) has shown that controlled atmosphere storage was not advantageous for carrot
storage, and recommended the use of modified atmosphere packaging.
Low O2 or high C02 levels may be of benefit for very short-term preservation of
vegetables, as for example, with asparagus (Torres-Penarada and Saltveit, 1994), banana
(Wills et al., 1990) and some vegetables (Wills et al., 1979). Low O2 or high C02
conditions result in partial or full anaerobic respiration and produce volatile compounds
(acetaldehyde and ethanol) responsible for aroma of fresh fruits (Morris et ai., 1979; Paz
et al., 1981). However, excessive accumulation of volatile compounds may lead to off-
flavours and some physiological disorders (Ke and Kader, 1989). A study on the effects
of low 02 and high CO2 levels on tomato physiology and composition showed that fruits
treated with low O2 or high CO2 had skin injury and blotchy ripening (Klieber et ai.,
1996). The incidence of fruits showing disease when ripe, increase with increasing
treatment time with O2 and CO2 (Klieber et al., 1996). Sozzi et al. (1999), on the other
hand, reported that keeping tomatoes in controlled atmospheres, even in the presence of
ethylene, had marked residual effects. These results suggested an antagonism between
elevated CO2 or low 02, and exogenous ethylene levels, which could determine most of
the physiological behaviour under controlled atmosphere storage, though a direct
regulatory mechanism by 02 and/or CO2 should not be discarded. The literature cited
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Literature Review
indicated that controlled atmosphere storage of tomatoes in conditions of low 02 and
C02 atmosphere might have economic benefits for very short-term storage of a few
days.
2.5.2.2. Modified atmosphere packaging (MAP)
Historically, modified atmosphere packaging (MAP) has been erroneously described
as synonymous with controlled-atmosphere storage (CAS) or controlled-atmosphere
packaging (CAP). Modified atmosphere packaging (MAP) is defined as the "packaging
of perishable products in an atmosphere which has been modified so that its
composition is other than that of air" (Hintlian and Hotchkiss, 1986). MAP storage
implies a lower degree of control of gas concentrations as compared with controlled
atmosphere and vacuum packaging. Typically, initial atmospheric conditions are
established for a transient period, and the interplay of the commodity physiology and the
physical environment maintain those conditions within broad limits (Zagory and Kader,
1988). Modified atmosphere is depletion of oxygen (02) and emanation C02, occurring
within a sealed plastic packaging headspace. This happens when fruit and vegetables are
respiring. Modified atmosphere packaging can be created either as a result of
commodity respiration (passive) or intentionally through active packaging (Zagory and
Kader, 1988). Passive modified atmosphere can be achieved in hermetically sealed
packages due to commodity respiration. Levels of O2 and C02 concentrations then
adjusted themselves to the commodity-desired range as a result of 02 consumption and
CO2 evolution during storage. If a commodity's respiration characteristics are matched
to the film permeability value, the optimum favourable modified atmosphere can be
created for a specific product (Smith et al., 1987b).
The atmosphere created by MAP depends on product, environmental and packaging
film factors. Product factors include respiration rate, respiration quotient, quantity of the
product, and 02 and C02 concentrations necessary to approximately achieve optimum
reduction of product aerobic respiration rate. Packaging film factors consists of
permeability of polymeric packaging materials to O2 and C02. and water vapour at a
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Literature Review
selected storage temperature. Temperature, relative humidity, light and sanitation
represent the environmental factors. This indicates that as many factors as possible
should be included during MAP of fresh vegetable trials (Zagory and Kader, 1988). A
proper understanding of the basic principles of the physiology, chemical, biochemical
and microbiological properties of vegetables during MAP storage is required for the use
of this technology.
2.5.2.2.1. Physiological changes
The beneficial effect of MAP on increasing shelf life of perishable products is
partially due to the decrease in O2 and the increase in C02 levels, and partially to the
decrease in physiological loss in weight (Biale, 1946 and 1960; Fidler et al., 1973;
Isenberg, 1979; Smock, 1979; Ben-Yehoshua et al., 1983). The role of MAP is to
primarily reduce respiration rate of fruit and vegetables by retarding metabolic activities.
Reduced respiration also retards softening, and slows down various compositional
changes associated with ripening (Kader, 1986).
It is obvious that plant tissue responds quickly to low 02 or high C02 levels during
MAP storage. Low O2 levels were shown to reduce the rate of respiration and resulted in
a delay in climacteric onset of the rise in ethylene levels and a decrease in the rate of
ripening (Fidler et al., 1973; Kader, 1986; Kannelis, et al., 1990; Yang and Chinnan,
1988a, b; Kannelis et al., 1991). Hypoxia conditions (low 02 levels) have shown to
inhibit the accumulation of RNA, protein, and DNA synthesis associated with the
wounding of vegetables (Butler et al., 1990). The lowest limit of O2 level, which can be
tolerated by vegetables, is a critical factor that must be taken into consideration in
selecting proper MAP for fruits and vegetables such as carrots and tomatoes (Butler et
al., 1990).
Burg and Burg (1967) have shown that the C02 level is a competitive inhibitor of
ethylene production during storage, and metabolic activities are reduced through an
increase in C02 levels in the headspace. Low O2, high C02 or both decreases the
production of ethylene during MAP storage, which means lower rates of respiration, and
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Literature Review
prolongs the shelf life of produce (Blackman, 1954; Aligue, 1995; Agar and Streif,
1996; Petracek et al., 2002). This is for the benefit of both climacteric and non-
climacteric fruits and vegetables during storage. The levels of C02 and O2 in the
headspace of packages balance each other and have a coupled effect on the metabolic
activities of fresh produce during storage. The effect of lower O2 and higher CO2 levels
on respiration is additive and can reduce respiration more than effected separately
(Kader et al., 1989). These means high levels of C02, when coupled with low O2 levels
have a cumulative effect on the respiration rate.
Oxygen and CO2 levels below or above the optimum levels specific to each fruit or
vegetable can cause physiological damage. Exposure of fresh commodities to extreme
levels of 02 and C02 below and above that required for normal respiration, may initiate
anaerobic respiration and lead to the development of off-flavours due to the
accumulation of ethanol and acetaldehyde (Zagory and Kader, 1988). Increased C02 is
also associated with an increase of acidity in plant tissues with a subsequent reduction in
pH. This acidification could lead to inactivation of enzymes, or phytotoxicity by CO2•
2.5.2.2.2. Chemical and biochemical changes
The loss in firmness, development of off-flavours, and discoloration of fresh and
minimally processed commodities after harvest or during ripening or storage, is the
result of various biochemical changes and was reviewed in section 2.4.6. A review on
the biochemical basis for effects of MAP on fruits and vegetables by Kader (1986)
indicated that biochemical and compositional changes such as color, texture (firmness),
flavour, and nutritive value can be reduced due to the modified atmosphere created by
MAP during storage. MAP may inhibit enzymatic activities responsible for the
deterioration in the mentioned quality parameters of fresh commodities during storage.
The loss of chlorophyll and lycopene synthesis is reduce when tomatoes are stored in a
modified atmosphere of less than 4% 02 and 4% C02 for 2 months (Goodenough and
Thomas, 1980). The appearance of PG is delayed for up to 8 weeks in green mature
tomatoes stored in 5% O2 and 5% C02 at 12.5°C (Goodenough et al., 1982), suggesting
36
Literature Review
delayed fruit softening. Burton (1974) reported that the changes in starch to sugar
conversion is slower in packaged fruit and vegetables with a headspace containing 5-
20% CO2 or less than 3% O2 at 2°C.
Under MAP the effect of polyphenoloxidase and tyrosinase, the enzymes responsible
for browning of plant tissue, decreases as a result of limited availability of O2 as a
substrate (Anese et al., 1997). A reduction in 02 levels or increase in C02 levels in the
microenvironment of a crop by MAP could reduce enzymatic activities responsible for
quality deterioration (Duckworth, 1966; Ruall and Lipton, 1979; Ryall and pentzer,
1982; Kader et al. 1985). However, the effect of low O2 created during MAP on
biochemical changes cannot be separated from the effect of increased C02 (MUITand
Morris, 1974; Bown, 1985; Siriphanich and Kader, 1986; Ballantyne et al., 1988b).
Barth et al. (1993) reported that MAP of broccoli stored at 20°C for 96 hr resulted in a
significant decrease of POX after 24 hrs compared to POX activities in unpackaged
samples. The chemical compositions such as ascorbic acid and total chlorophyll also
remained higher in packaged broccoli, but 02 levels below 3% increases the
concentrations of ethanol and acetaldehyde, and activities of pyruvate decarboxylase
and alcohol dehydrogenase, which results in ethanolic fermentation in fresh-cut carrots
(Kato-Noguchi, 1997).
This review shows that MAP has an effect on the biochemical as well as chemical
changes in fruits and vegetables during ripening and storage through reducing the levels
of 02 and increasing the levels of C02 in the headspace. Generally, the lower the O2
concentrations achieved by the MAP the lower the rate of chemical as well as
biochemical changes, resulting in reduced respiratory metabolism and other biochemical
processes, and leading to retention of chemical quality characteristics. However,
maintenance of optimum minimum O2 concentration inside the packages is very
important to avoid accumulation of excessive volatile compounds responsible for off-
flavour and physiological disorder. This entails the need for selection of appropriate
packaging material for the specific fruits and vegetables.
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Literature Review
2.5.2.2.3. Microbiological changes
The extended shelf life of many MAP may allow extra time for microorganisms to
reach dangerously high levels in a food. Even in the case of slow growing photogenic
microorganisms, extended shelf life using MAP gives them sufficient time to multiply,
if not properly managed during storage. Additional research in the microbial control on
MAP foods is still needed.
Hao et al. (1999) studied microbiological quality and production of botulinum toxin
in MAP of broccoli, carrots, and green beans. Types of packaging material affected the
quality of vegetables without noticeably influencing the growth of microorganisms.
These results created awareness that the use of MAP could have both positive as well as
negative effects on the microbial flora associated with fruits and vegetables during
storage based on the pre-packaging treatment and storage conditions. However, their
result showed that the toxin was not detected in the vegetables under study.
Microorganisms require certain conditions to grow and reproduce. These conditions
are either properties of food such as nutrients, pH and water activity or extrinsic
properties of food associated with storage environment such as oxygen, light,
temperature and time. The most important environmental factors are gaseous
composition and temperature. Modified atmosphere packaging in principle controls
these factors to reduce or suppress spoilage and extend shelf life of fresh produce. Anese
et al. (1997), studying the effect of modified atmosphere packaging on microbial
growth, have shown that C02 and N2 levels were the most effective in inhibiting
microbial growth. Concentrations of CO2 in excess of 5% inhibit the growth of
microorganisms of most foods. However, the pH of MAP foods increases with increase
in carbon dioxide concentration in packages. Direct suppression of microorganisms by
MAP has only been possible with the horticultural commodities that can withstand
carbon dioxide levels at 20% or above without development of off-flavours, odours, and
colours (Harvey, 1982; Aaron 1989). The ability of modified atmosphere alone is not
sufficient to limit the incidence of spoilage of fruits and vegetables. The necessity of
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Literature Review
pre-packaging treatments to reduce initial microbial load, as well as limiting their
growth during storage, is critical.
Conversely, unsuitable MAP can prevent wound healing, speed up senescence, or
incidence of physiological breakdown, making fruits and vegetables more susceptible to
postharvest pathogens. EL-Goorani and Sommer (1981) suggested that O2 levels below
1% of CO2 levels above 10% could be utilised to limit the growth of yeasts and moulds.
In summary, the growth of microorganisms is likely to continue inside MAP
vegetables and fruits, especially for those that need higher O2 and lower C02 levels.
Additional pre-packaging treatments are therefore still required.
2.5.2.2.4. Postharvest factors affecting MAP
The microenvironment created and maintained in the headspace of a package is the
net result of the interaction of commodity factors, environmental factors and packaging
material characteristics. Zagory and Kader (1988) described the effects and development
of modified atmospheres in the packaging of fresh produce. In order to maintain quality
of fruits and vegetables, the product, environmental and packaging material factor must
be considered in creating favourable conditions for MAP of fresh produce in order to
keep the quality. Therefore, in this section a brief description of commodity factors and
environmental and packaging material factors for MAP will be presented.
2.5.2.2.4.1. Commodity factors
In order to develop an appropriate modified atmosphere environment in packages
several product factors needs to be understood. These includes the rate of O2 uptake and
CO2 evolution, permeability of packaging films to 02 and C02, tolerance of plant
materials to levels of these gases and diffusivity of fruits and vegetable skin and flesh to
O2 and C02 (Fidler et al. 1973; Isenberg, 1979; Smock, 1979; Kader, 1985; Salveit,
1989). Zagory and Kader (1988) classified the commodity factors affecting the
effectiveness of MAP according to resistance to gas diffusion, respiration, ethylene
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Literature Review
production and sensitivity, optimum temperature, relative humidity, and gas
concentrations
Resistance to gas and water diffusion across the plant material varies with different
vegetables or fruits, cultivars, plant organs and stage of maturity (Cameron and Reid,
1982). The resistance to gas diffusion is affected more by anatomical difference than
biochemical differences among various vegetables and fruits (Burton, 1974). However,
the rate at which O2 passes through skin or epidermal tissue depends on the 02 gradient
(Kader et al., 1989; Burg, 1990). In some commodities the skin and epidermal tissue
may posses pores, called stomata, and lenticles, which are the passages for the 02.
Cranberry, tomato and green pepper skins contain no pores, and all gases diffuse
through holes in the pedicel scar. The resistance of gas diffusion through the boundary
gas layer and skin of most fruits and vegetables varies with the type of gases, i.e. O2,
C02 and ethylene (Burg, 1990). The rate of gas diffusion from the surface of the product
to the interior also depends on the proportion of gas space. In the case of minimally
processed fruits and vegetables, the released cellular fluid flows into the gas space and
blocks gas transfer. Diffusion of gas would be much slower in cell sap than in the gas-
filled intercellular spaces (Burg, 1990). In general, the structures such as the skin, the
cell wall, the intercellular space and the cytosol are the barriers of O2movement to the
mitochondria in the cell.
The respiration of fruits and vegetables was discussed in section 2.4.1., but without
taking into account packaging films and MAP. The effectiveness of packaging films
can be evaluated by their ability in keeping the normal respiration rate of produce
without decomposition. Based on the rate of respiration, fruits and vegetables are
classified as climacteric or non-climacteric. Tomato and carrot are classified as
climacteric fruit and root vegetables, respectively, with moderate respiration rates
compared to the other fruits and vegetables. The respiration rate increases consistently
with an increase in storage temperature. The respiration rate of topped carrots is from
10-20 mg kg-I. h-I and 46-95 mg kg". h-I at O°C and 20-21°C respectively. For mature
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Literature Review
green tomatoes the respiration rate varies from 5-8 and 28-41 mg kg". h-I at 4-5°C and
20-21°C storage (Salunkhe ef al., 1991). Thus, it is apparent that a reduction in storage
temperature is an effective means of extending the commercial life of tomatoes and
carrots using MAP.
The rate of ethylene production of fresh produce, and the sensitivity to this hormone,
determines the type of packaging film appropriate for secured quality maintenance and
shelf life extension (Zagory and Kader, 1988). Tomato produces 1-10 mg CO I2• kg-I. h-
ethylene, which is moderate compared to some other fruits (Kader ef al., 1985). Very
low concentrations of ethylene are required to advance biochemical and physiological
changes during storage and accelerate the ripening processes of carrots and tomatoes.
The effect of ethylene on fruits and vegetables that can be stored at a temperature range
of 0 to 4.4°C is not possible to detect. The recommended storage temperatures for
carrots range from 0 to 1°C and hence the effect of ethylene on carrot during storage at
this temperature is negligible. The recommended storage temperature for tomatoes is
varying from 8 to 13°C, which is sufficiently high for production of ethylene, and
should be considered as a postharvest factor affecting the shelf life of tomatoes.
A reduction in ethylene production and sensitivity associated with MAP can delay
the onset of climacteric and prolong the storage life of these fruits (Zagory and Kader,
1988). Even non-climactreric fruits and vegetables can benefit from reduced ethylene
sensitivity and lower respiration rate attributed to MAP. Ethylene production is reduced
by ether low O2, high C02, or both, and the effects are additive (Zagory and Kader,
1988).
2.5.2.2.4.2. Environmental factors
Air temperature, relative humidity and natural microbial flora of perishable produce
are the main environmental factors affecting the effectiveness of modified atmosphere
packaging (Zagory and Kader, 1988). Packaged fruits and vegetables have specific
ranges of temperature optima for their normal respiration. Below this limit, fruits and
vegetables can easily by affected by chilling injury, which advances to high respiration,
41
Literature Review
hastened senescence and short shelf life. The optimum storage temperature for a specific
fruit or vegetable is the one that delays senescence, and maintains quality the longest
without causing chilling, freezing, or other injury (Zagory and Kader, 1988). The
optimum temperature for tropical fruits is above 13°C, because these fruits are sensitive
to chilling injury. Non-chilling-sensitive commodities can be stored near O°C without
negative effect. Previous studies indicated that the effect of reduced O2 and elevated
C02 had an effect on chilling injury (Lyons and Breidenbach, 1987). Chilling injury of
fruits and vegetables reduced with low 02 and high C02 concentrations in the storage
atmosphere (Lyons and Breidenbach, 1987). The optimum temperature range for carrot
and tomatoes are 0-5 and 8-13 °C, respectively (Salunkhe et al., 1991). In general,
optimum temperature is a key factor in reducing respiration, production of ethylene,
chilling injury, enzymatic activities, proliferation of microorganisms during storage of
fruits and vegetables, although modified atmosphere packaging expands the limit of
optimum temperature.
The danger associated with high relative humidity is the condensation in packages, .
which creates favourable conditions for microbial growth. Condensation on the package
film affects the permeability property and creates unfavourable interior conditions
during storage. Proper temperature maintenance throughout the postharvest handling
lines is central to prevent the incidence of condensation in films. On the other hand, low
relative humidity increases the loss of moisture from fruits and vegetables (Kader,
1987). The optimum range of relative humidity for carrot storage varies from 90-100%,
whereas for tomatoes the range can vary from 85-90% (Salunkhe et al., 1991)
2.5.2.3. Packaging films
Selection of appropriate films for MAP storage of fresh vegetables on their
effectiveness in protecting produce during shelf life is critical (Arthey and Dennis, 1991;
Perry, 1993; Wiley, 1994; Farber and Dodds, 1995). The principal plastic materials for
MAP that can be used with intact vegetables and fruits include polybutylene, LDPE,
HDPE, PP, PVC, PS, VA, ionomer, Pliofilm, and PVDC (Schlimme and Rooney,
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Literature Review
1994). Permeability of packaging film to O2 and CO2 varies with type of packaging film
material or composition. The characteristics of the main types of plastic films with their
potential uses in MAP are summarized in Table 2.1 (Schlimme and Rooney, 1994). The
Table 2.1. Permeability characteristics of several plastic films with potential for use as
MAP of fresh and lightly processed produce (Schlimme and Rooney, 1994).
Transmission Rate
Film Type 02* C02* H20 va~our**
Low-density polyethylene (LDPE) 3900-13000 7700-77000 6-23.2
Linear low density polyethylene (LL DPE) 7000-9300 16-31
Medium-density polyethylene (MDPE) 2600-8293 7700-38750 8-15
High-density polyethylene (HDPE) 52-4000 3900-10000 4-10
Polypropylene (PP) 1300-6400 7700-21000 4-10.8
Polyvinylchloride (PVC) 620-2248 4263-8.138 >8
Polyvinylchloride (PVC), plasticized 77-7750 770-55000 >8
Polystyrene (PS) 2000-7700 10000-26000 108.5-155
Ethylene vinyl acetate copolymer (12% VA) 8000-13000 35000-53000 60
Ionomer 3500-7500 9700-17800 22-30
Rubber hydrochloride (Pliofilm) 130-1300 520-5200 >8
Polyvin~lidine chloride (PVDq 8-26 59 1.5-5
*Expressed in terms of crrr' m-2dail at 1 atm.
**Expressed in terms of g m-2dail at 37.8°C and 90% RH.
table shows that the transmission rate for 02 varies from 8 up to as high as 13,000 crrr'
m-2 dail at 1 atm for PVC and LDPE packaging films, respectively. The transmission
rate of packaging materials for CO2 also varies from 59 up to 77,000 (crrr' m-2dail at 1
atm), which is quite a large variation, the lowest permeability being for PVDC and
highest for LDPE. The water vapour transmission rate also varies from 1.5 to 155 g m-2
dail. The variation in permeability of packaging films to 02, CO2 and H20 could give a
wide range of choices for films appropriate for specific commodities.
Temperatures have effects on the permeability of packaging films. As temperature
increases, the film permeability increases, which may affect the passive modified
atmosphere that the film is designed for. Permeability of CO2 is affected more than O2
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Literature Review
permeability, implying that a film that is a suitable packaging material at one
temperature may not be so at another (Zagory and Kader, 1988). Kader et al. (1989)
reported that most common films are relatively good barriers to moisture vapour,
because they maintain high internal humidity even in dry, ambient conditions. This
means that relative humidity affects the permeability of packaging films less than
storage temperature. However, condensation inside films decreases the permeability of
C02 and O2 (Rodov, 1995).
It is obvious that the quality of fresh commodities can be dependent on the types of
packaging film used for MAP. Under poor modified atmosphere storage management,
occurrence of anaerobic metabolism is also possible in commodities packaged in films
with low permeability to 02, C02 and water vapour. Losses in physiological weight are
higher from fresh commodities packaged in low-density packaging films than in high-
density films. However, because near ambient O2 level is maintained in the headspace of
packages, the occurrence of anaerobic metabolism of fresh commodities could be
avoided with the use of packaging films with higher permeability to 02, C02 and water
vapour during storage. Lower weight loss and firmness of tomatoes were maintained
better in polyolefin bags (0.015 mm thick) than in PVC (0.0177 mm thick) during 5
weeks of storage at 10°C and 80% relative humidity (Frezza et al., 1997). The shelf life
of tomatoes was extended better when packaged in polyethylene and PP films as
compared with PVC bags (Batu and Thompson, 1998). The lowest weight losses and the
highest soluble solids contents after 60 days of storage were found in tomatoes packaged
in polyethylene and PP films. Shelf life studies of pink ripe tomatoes packaged in
polyethylene films with 100, 200 or 300 gauge showed that freshness was best
maintained in perforated films compared with the other (Singh et al., 1996). The reason
for this may be due to higher permeability to gases of the two films as compared with
polyvinyl chloride.
MAP using LDPE delayed changes in acidity, soluble solids, texture, colour and PG
activity, and resulted in substantial reductions of weight loss of tomatoes, while higher
44
Literature Review
density films showed the lowest weight losses, and the highest soluble solids content
after 60 days of storage (Nakhasi et al., 1991). However, it could be possible that the
higher microbial populations found in these packages were due to relatively a higher
storage temperature (13°C) and moisture accumulation in the headspace of packages.
Ben- Yehoshua et al. (1998) has shown that perforating the film affected the
concentrations of both 02 and CO2 and water condensation without affecting the relative
humidity of the air in the package headspace. The perforated film prevented the decay
and maintained the postharvest quality of vegetables and fruits compared to storage in
open boxes. Polyethylene bags with 2-4 diffusion holes per 4 kg tomatoes gave the best
results, as the CO2 permeability was improved (Esquerra and Bautista, 1990). Similarly
LDPE bags were found to be better in maintaining the quality of carrots during storage
compared with high-density polypropylene bags (Seyoum et aI., 2001). This indicated
that the microperforated packaging films maintain the best quality of tomatoes during
MAP. The strategies for combining films or film and mieropore combinations could
lead to realistic solutions to meet the required gas transfer properties (Exama et al.,
1993).
The common films, such as PVC and LDPE, can satisfy the gas flux requirements of
low respiring tissues of carrots (Exama et aI., 1993). Emond et al. (1995), on the other
hand, showed that perforated films significantly reduced water loss and condensation in
packages of carrots during storage at 2°C and 95% relative humidity, compared to
unperforated films. Nazar et al. (1996) showed that perforations in polyethylene bags
equivalent to 0.5% of the total effective surface area of the package had no effect on the
shelf life of carrots. The packaging film permeability also greatly influences disease
incidence and sprouting of carrots during storage (Lingaiah and Reddy, 1996), as did
non-ventilated polyethylene bags (Lingaiah and Reddy, 1996).
2.5.3. Progress on evaporative cooling of vegetables
The effect of storage temperature as an environmental factor during packaging was
reviewed in 2.5.2.2.2. with emphasis on optimum temperatures for specific fruits and
45
Literature Review
vegetables, e.g. 1°C for carrots and l3°C for tomatoes. To maintain these temperatures,
refrigeration is normally required. Due to the mechanical complexity and expense, such
practices are not available in most developing countries. Concurrently, postharvest
losses are high, e.g. estimated at 25-35% in Ethiopia (Agonifer, 1991) or even at 40% in
developing countries in general (FAO, 1981). Alternative storage methods with
controlled temperature and humidity could be sought that are mechanically less complex
and also less expensive. Evaporative cooling methods could be an answer.
Little work has been devoted towards the application of evaporative cooling
principles in the field of fruit and vegetable preservation, with most of the work having
been carried out in India and USA (Rama et al., 1990; Rama and Narasimham, 1991;
Royand Pal, 1994; Christenbury et al., 1995; Thompson and Kasmire, 1981; Thompson
eta!.,1998.).
Rama et a!. (1990), in India, showed that a metallic EC chamber reduced weight loss
of potatoes compared to those stored at ambient conditions (20-30°C, RH 40-80%).
Similar fmdings were obtained on physiological weight loss during EC storage of fresh
commodities by Dzivama et al (1999). Royand Pal (1993) have developed a zero energy
cool chamber. The cooler increased the shelf life of tropical fruits by 2 to 14 days (15 -
27% increase) compared to storage at ambient temperature. Lower PWL and loss of
vitamin A and C content were observed in fruits stored in a zero-energy cool chamber
compared with fruits stored at room temperature (Kumar and Nath, 1993). Other
findings also showed that weight loss was 3 times greater under ambient conditions than
in a zero energy evaporative cooling chamber until tomatoes reached a red-ripe stage
(Gopalakrishna et al., 1991). It was indicated that the ripening time was extended with
extended shelf life from 6.25 (ambient) to 10 days by cool storage. Acedo-AL (1997)
showed that tomato fruits harvested at mature-green and stored in evaporative cooling
storage had much less weight loss and shrivelling and a longer storage life than fruits
kept at ambient conditions with significantly delayed ripening. Dzivama et a!. (1999)
evaluated application of evaporative cooling for storing mangoes, bananas and
46
Literature Review
tomatoes. Results indicated that the produce remained in good condition for 18 days in
the cooler, compared to 9 days in ambient conditions.
Under Ethiopian conditions a naturally ventilated evaporative cooler was designed
and constructed using locally available and low cost materials (Seyoum and W/Tsadik,
2000). The cooler was able to significantly reduce the storage temperature and increase
the relative humidity of air within, compared to that of the surrounding climatic
conditions. The average reduction in air temperature inside the cooler was found to be
S°c. below environmental air temperature, with an average rise of 26% relative
humidity. As a result it was possible to store mangoes for more than two weeks in the
cooler without deterioration in appearance quality. Twenty-two percent of the mangoes
stored at ambient conditions perished after 10 days of storage compared to 0.87% of the
cooled samples.
The studies cited here were more devoted to natural ventilation cooling of fruits and
vegetables during which only few postharvest quality parameters such as weight loss
were monitored. However, a wider range of quality parameters should be included in
order to understand the extent of postharvest quality (physiological, chemical and
microbiological) changes occurring during EC storage. For instance, fresh produce may
appear good, while microbial populations might thrive as a result of higher than
optimum storage temperatures achieved in cold storage facilities and other than
optimum humidities for specific fruits or vegetables.
2.6. Summary
The literature survey shows that any preharvest treatment, either to improve yield or
quality, has an effect on fresh commodity quality at harvest and during storage. It is
clear that not all the reviewed conditions could be optimised simultaneously. The
reviewed conditions were also not described for specific cultivars of a vegetable type.
This means that many of these conditions will have to be accepted as constant in a
study, e.g., agricultural practices and environmental conditions, with focus on a few
47
Literature Review
selected variables, e.g. ComCat® treatment, postharvest disinfection and storage
temperature.
The postharvest performance of high yield ComCat® treated vegetables, e.g. carrots
and tomatoes have not yet been investigated. The reviewed literature on postharvest
performance of carrots and tomatoes stretches over several years and the research was
carried out in many countries, while using different experimental approaches. These
could therefore not be used as references against which to measure the ComCat® treated
vegetables. Experiments will have to be designed carefully and proper controls will have
to be incorporated.
Postharvest treatments of vegetables include disinfecting, and use of MAP and cold
storage. According to the literature survey, disinfecting methods can generally be
classified as chemical, biological, and physical methods. Although several chemicals
and biological products are available on the market their success remains limited due to
variability experienced in their effectiveness and lack of experience on how to adapt
them to the commercial settings. The literature shows that chlorine treatment is
currently the most commonly used, easiest to use and the cheapest method, but not
necessarily the most effective. It is very effective for control of microorganisms, but
almost no knowledge is available on its effect on the physiological aspects of harvested
vegetables. It would therefore be necessary to include a second disinfectant in the study
in order to avoid misleading results of disinfectant on ComCat® treated vegetables.
Anolyte, an electrochemically activated water seems to be a good candidate for such a
control. Itwas shown to kill and limit the growth of microorganisms. Chemical methods
have residues that have negative impacts on health and environment or ecology, while
physical methods need high initial investment. This encourages further research not only
for microbiological safety, but also to develop environmentally and ecologically safe
sustainable disinfectants as a partial or complete substitution for chemicals.
Regarding extended shelf life, the literature pointed to MAP and specific storage
temperature for best results. New packaging material is constantly reaching the market,
48
Literature Review
so that those aspects should be the final methods to test the postharvest performance of
ComCat® treated vegetables. MAP, combined with cold storage are the most popular
method as a result of its efficiency in increasing the shelf life of fresh commodities
without much quality deterioration, less operational and material cost and easy
consumer packaging. The optimum temperatures to store carrots and green mature
tomatoes were reported to be 1°C and 13°C, respectively.
The observation that ComCat® can increase harvest yield of vegetables may be
effectively used for food security purposes in underdeveloped countries when
production is immediately followed with sustainable preservation technology. Despite
high market demand after production, 20-50% of commodities is lost before reaching
consumers in these countries due to a shortage of cooling facilities. The optimum
storage temperatures, such as those for carrots and tomatoes mentioned above, can thus
not be met. An attempt will be made to explore a low-cost vegetable preservation
technology and look at the storability of the high harvest yield ComCat® treated carrots
and tomatoes under higher storage temperature using EC. According to reviewed
literature, evaporative cooling is cheap, easy to install and maintain, and was therefore
proposed to be explored as an alternative cool storage tool in developing countries.
49
CHAPTER3
EFFECT ofPRE- and POSTHARVEST
TREATMENTS on PHYSIOLOGICAL, CHEMICAL
and MICROBIOLOGICAL QUALITIES of
CARROTS
Abstract
Quality changes in preharvest ComCat® treated and untreated control carrots stored
at 1 ± 0.5cC and ambient temperatures (16.7-29.5°C) and relative humidity (31-68%)
were studied for more than 4weeks. The carrots were analysed for headspace gases (02,
CO2, and N2), physiological weight loss (PWL), total soluble solids (TSS), total
available carbohydrates (TAC), sucrose, glucose, fructose, ascorbic acid (AA) content,
peroxidase (POX) activity, aerobic bacteria, yeasts and fungi, and coliforms. The effect
of chlorinated and anolyte water disinfecting treatments coupled with MAP was
investigated. ComCat® treated carrots had less aerobic and coliform bacteria at harvest
as well as higher levels of TSS, TAC sucrose and sucrose-hexose ratio, and lower
glucose and fructose concentrations. Preharvest ComCat® treatment reduced PWL in
carrots during storage, TSS content was better maintained, and a general trend of lower
sucrose, glucose, fructose and total soluble sugar concentrations were found during
storage. The concentrations of TAC seemed to accumulate better in ComCat® treated
than in control carrots stored at room temperature. The preharvest ComCat® treatment
had no significant effect on AA content and POX activity of carrots during storage,
although it had a slightly higher AA at harvest. Two disinfecting treatments, chlorinated
and anolyte water dipping, were compared. During storage, these treatments when
coupled with MAP also had significant effects on PWL, TSS, TAC, sucrose and
fructose content of carrots. Chlorine disinfecting resulted in an etched surface, which
was not observed for anolyte treatment. Anolyte water showed a better positive effect
on PWL compared with chlorine solution. Disinfecting carrots in anolyte water
50
Chapter 3. Carrot Storage (1 'C)
significantly maintained the AA content and decreased the level of POX activity. A
short time of 5 min dipping of carrots in anolyte water was found to be as effective as a
20 min in chlorinated water treatment, significantly reducing growth of aerobic bacteria,
fungi and coliforms in carrots during storage. Storage temperature significantly affected
all postharvest quality parameters tested in carrots during storage. Higher temperatures
rapidly deteriorated microbiological, physiological and chemical quality characteristics
of carrots. The combined effect of pre-and postharvest treatments such as ComCat®,
disinfecting, packaging and low temperature storage treatments had a significant
positive effect on maintaining postharvest quality and improvement of the shelf life of
carrots.
3.1. Introduction
Horticultural commodities are different from other foods with their high levels of
respiration and other metabolic processes associated with maturation, ripening, and
senescence after harvest. During development and storage, carrots undergo a complex
series of physiological, biochemical and microbiological events involving changes in
postharvest quality (Phan et al., 1973, Nilsson, 1987, Hole and McKee, 1988, Rosefeld
et al., 1998, Suojala, 1999, Suojala, 2000). During storage, levels of O2 and CO2 are
critical for carrot quality. With the use of modified atmosphere packaging (MAP)
metabolic activities may be reduced by controlling the levels of O2 and CO2 in packages
of fresh commodities (Zagory and Kader, 1988). Temperature and relative humidity are
other important factors that affect the quality and shelf life. Low temperature reduces
the rate of respiration and biochemical activities, which are responsible for quality
changes of carrots (Zagory and Kader, 1988). It was also shown that the respiration rate
of carrots can be affected by preharvest treatments, so that the respiration rate is lower,
and therefore leading to longer shelf lives (Salunkhe et aI., 1971). The preharvest
histories of vegetables are therefore very important, as fresh produces are responding
differently to postharvest factors. A preharvest treatment, CorrrCat'", has been developed
recently from plant extracts, which was shown to improve vegetable yield, general
51
Chapter 3. Carrot Storage (1 CC)
strength and development of plants, and activate inherent plant defence mechanisms via
induced resistance (Huster, 2001). In South Africa, the preharvest ComCat® treatment
increased carrot yield by 32% (Schnabl et al., 2001). Investigation on quality of
ComCat® treated carrots both at harvest and during storage is yet to be explored.
During storage microorganisms are the most important factors in postharvest
vegetable quality management and postharvest vegetable and fruit decay (Harvey,
1978). Vegetables are usually treated with chlorinated water after washing to reduce
microbial load prior to packaging (Bolin et al., 1977). Much work has been done on the
development of alternative methods to control postharvest decay (Rodov et al., 1995
and 1996; Fallik et al., 1999; Fallik et al., 2000; Afek et al., 1999).
One alternative could be the use of electrochemically activated saline water (anolyte
water), which is safe from both an environmental as well as an ecological point of view.
The objectives of this chapter were: (1) to investigate postharvest properties of
ComCat® treated carrots; (2) to investigate anolyte water as an alternative disinfectant to
a chemical treatment such as chlorine to reduce microbial load and suppress their
growth thereafter during storage; and (3) investigate the storage quality of preharvest
ComCat® treated carrots using MAP at 1°C and ambient temperature.
3.2. Materials and Methods
3.2.1. Carrot production
Carrots were planted in the Bloemfontein area, South Africa. During the growing
period, carrots were treated twice with ComCat®. Experimental plants were treated with
109 ha-I ComCat® in 350 I of water, and control plants with 0 g ha-I. Carrots were
sprayed once at the three leaves stage, and a second time at a vegetative stage. All other
agricultural practices were kept the same between the treatments during carrot
production. At a maturity stage of 5 months, carrots were harvested and topped in the
field, and were immediately transported the vegetable laboratory of the University of
Free State. The topping, harvesting and transportation of carrots were made early in the
52
Chapter 3. Carrot Storage (1 'C)
morning before the temperature was too high. For protection against mechanical injury
during transportation, carrots were packed in plastic crates. ComCat® treated and
untreated carrots were harvested manually from four randomised blocks each and
delivered to the laboratory immediately after harvest. After delivery to the laboratory,
carrots were topped by carefully retaining the crown of the root. Carrots free of
blemishes or defects were selected. The working surfaces and all tools used for topping
carrots were washed and disinfected prior to use by 1% Chlorobac (Syndachem, Pty,
LTD). Immediately after delivery to the laboratory, the carrots were hand washed with
water at a temperature of 4°C, to remove field heat, soil particles and to reduce
microbial populations on the surface. Prepackaging disinfecting treatments and
packaging of carrots were performed on the same day.
3.2.2. Postharvest treatment
After washing, a total amount of 144 kg ComCat® treated carrots were sub divided
into three groups of 48 kg each, in preparation for dipping treatments in chlorinated
water, anolyte water or tap water, at 4°C. Plastic containers were washed, disinfected
and rinsed with distilled water prior to use for the dipping treatments. Plastic containers
were used to avoid losses of charged ions from anolyte water to metal containers. Tap
water in these plastic containers was adjusted to 100)-lg.mrl free chlorine with sodium
hypochlorite (5% NaOCI). A 20 minutes dipping time in 100)-lg. mr! chlorine
supplemented water solution was selected, as this was reported to be the optimum
effective dipping time without significant effect on the overall quality of vegetables
(Nunes and Emond, 1999). The free chlorine was determined using a test kit from Hach
(Model CN-66; USA). The temperature was maintained at 4°C during the
measurements of free chlorine.
Anolyte water was prepared electrochemically from saline water containing 5%
NaCl with an ionyzer (Radical Waters Pty Ltd, South Africa) operating at a pressure of
50 kpa. The pH of anolyte water was adjusted to 6.1 and it contained 3.55% total
dissolved solids. Immediately after preparation, anolyte water was cooled to 4°C, and
53
Chapter 3. Carrot Storage (1 'C)
carrots were dipped without delay to avoid loss of inhibitory characteristics. The
optimum dipping time of carrots in anolyte water was determined as 5 minutes in a trial
experiment where carrots were dipped in anolyte water for 5, 10, and 20 minutes and
compared with the efficacy of20 minutes dipping in chlorinated water (100 ug. ml") on
microorganisms (Seyoum et al., 2002). Carrots that were dipped in tap water were
dipped for 20 minutes.
3.2.3. Modified atmosphere packaging
Low-density polyethylene (LDPE) bags were found to be the preferred packaging
film above polypropylene (PP) for storage of carrots at 1°C in a trial study (Seyoum, et
al., 2001). Other researchers recommend, microperforated LDPE for MAP of carrots
and tomatoes (Lipton 1977; Seyoum et al., 2001). In this study the microperforated bags
specifically designed and manufactured for carrot and tomato storage were therefore
used (Xtend® Film, Patent No. 6190710, StePac L.A., Ltd., Israel). Carrots were
subdivided and packaged as 1 kg-samples, and stored at 1°C or room temperatures. The
unpackaged 1 kg-sample carrots, for each treatment combination, were placed on
perforated plastic bags and left open during storage at 1°C or room temperatures.
On each sampling date, packages of carrots (Ikg each) were randomly taken in
triplicate from each treatment for quality analyses. A new package was taken each time
in order to maintain the micro environment and avoid contamination through repeated
opening and sealing.
3.2.4. Gas sampling and analysis
Micro atmosphere gas analysis was performed at days 0, 3, 5, 9, 17,25 and 32 of the
storage period. Gas samples were withdrawn from the package by piercing the test film
with a pressure lock syringe (Precision Sampling Crop, Baton Rouge, Lousiana) with a
fine needle and withdrawing a 5 ml gas sample (Ballantyne et al., 1988 a and b; Gunes
et al., 1997; Jeon and Lee, 1999). At each sampling date, three packages from each
storage condition were tested separately. CO2, O2 and N2 concentrations were analysed
54
Chapter 3. Carrot Storage (1 'C)
by gas chromatography (GC) on a Varian 3300 equipped with a Porapak Q 1.2 m X 2.3
mm stainless steel column, with thermal conductivity detection at 200 mA and H2 as
carrier at 19.5 ml. min-I flow rate for CO2 determination. For analysis of N2 and 02, a
0.8 m Molsieve column (PHASE SEP.) was used, with thermal conductivity detection
operated at 200 mA and H2 as carrier at 12.5 ml. min-I. The GC oven temperature was
set at 45°C for both analyses. The opening made by the needle during gas sampling was
immediately sealed with drawing tape, to avoid leaking of gas from the packages.
3.2.5. Physiological weight loss
The physiological weight loss (PWL) was determined usmg the methods as
described by Pirovani et al. (1997) and Waskar et al. (1999). The PWL was determined
by periodical weighing carrots on days 0, 7, 14, 21, 28, 35, 42 and 50 after packaging.
The differential weight loss was calculated for each interval and converted into
percentage by dividing the change with the initial weight recorded on each sampling
interval. The cumulative PWL was expressed in per cent with respect to different
treatments.
3.2.6. Chemical analysis
3.2.6.1. Total soluble solids (TSS)
The TSS was determined using the procedures as described by Waskar et al. (1999).
An aliquot of juice was extracted using a Kenwood juice extractor, and 50 ml of the
slurry was centrifuged for 15 minutes at 5000 x g at 4°C. The TSS was determined by
an Atago NI hand refractometer with a range of 0 to 32 °Brix, and resolutions of 0.2
°Brix by placing 1 to 2 drops of clear juice on the prism. Between samples the prism of
the referactrometer was cleaned with tissue paper soaked in methanol, washed with
distilled water and dried before use. The refractometer was standardised against distilled
water (0% TSS).
55
Chapter 3. Carrot Storage (1 CC)
3.2.6.2. Free sugar analysis
Free sugars, sucrose, glucose and fructose, were determined by the method of Riaz
and Bushway (1996). A 50 g carrot sample was homogenised for 2 minutes. Sugars
were extracted by placing aiO g aliquot in a 100 ml beaker and stirring for 1 minute
with 35 ml 95% ethanol. The samples were shaken 20 times and kept at room
temperature overnight. Samples were transferred to a 50-ml volumetric flask and made
to volume with 80% ethanol. After filtration, aliquots of 5 ml were placed in vials and
centrifuged for 5 minutes at 3000 x g (Beckman, Microfuge E) before analysis by high
performance liquid chromatography (HPLC). HPLC was carried out on a Waters
system (501 pump) and Biorad Aminex column (7.8 mm X 300 mm) with a differential
refractive index detector (R401) operated at 42°C and a mobile phase of de-ionized
water at a flow speed of 0.6 ml. min-I and temperature of 85°C.
3.2.6.3. Total available carbohydrate (TAC)
Total available carbohydrate was estimated by the Automated Clegg Anthrone
method (Cl egg, 1956, and Osbome & Voogt, 1978). A carrot puree of 2 g was
homogenised for approximately 2 minutes with 15 ml distilled water and 20 ml 99%
H2S04 and placed in an oven at 50°C for 15 minutes. A series of trail studies were
conducted on the effect of heating time and type of acid (perchloric and sulphuric acids)
to be used for hydrolysis to determine any variation in the values, however, no
difference was observed. The warm solution was thoroughly mixed for 5 minutes with
an electric stirrer, transferred to a 250-ml volumetric flask and made up to the mark with
distilled water. The extracted samples were refrigerated until analysed the next day.
Aliquots were placed in vials and analysed by aTechnicon AutoAnalyzer.
3.2.6.4. Ascorbic acid analysis (AA)
The ascorbic acid content (AA) of carrots was determined by the 2,6-dichloro-
phenol indophenol method (AOAC, 1970). An aliquot of 10 ml carrot juice extract was
diluted to 50 ml with 3% metaphosphoric acid in a 50 ml volumetric flask. An aliquot
56
Chapter 3. Carrot Storage (1 'C)
was centrifuged at 10 000 x g for 15 minutes and titrated with the standard dye to a pink
end-point (persisting for 15 sec). The ascorbic acid content (%) was calculated from the
titration value, dye factor, dilution and volume of the sample.
3.2.6.5. Peroxidase activity (POX)
Carrot tissue (12.5 g) was homogenised in 25 ml of citrate-phosphate buffer (pH 6.5)
(made with 0.05 M citric acid and 0.1 M Na2HP04) for 2 minutes (Howard et al., 1994).
The homogenate was held at 4°C for 2 hr and centrifuged at 10 000 X g for 15 minutes
at 4°C. Prior to POX activity determination a reaction mixture was prepared by adding
0.05 ml of 1% o-dianisidine dye in methanol to 6 ml of 30% H202 substrate. Then 2.9
ml of this dye-substrate mixture was transferred to a 3 ml test cuvette. Enzyme
supernatant (0.1 ml) was introduced into the test cuvette from a 0.1 ml pipette with the
tip below the surface. The control consisted of the same reaction mixture, but with 0.1
ml extraction buffer instead of enzyme extract. The cuvettes were covered with
parafilm, and the solution mixed by inversion. The rate of peroxidase activity was
followed spectrophotometrically at 460 nm (Howard et al., 1994). The increase in
absorbancy was recorded at 15 seconds intervals for 2 minutes. POX activity was
expressed as increase in absorbancy at 460 nm g-I tissue min-I at 25°C.
3.2.7. Microbiological analysis
Microbial populations were estimated by the procedure followed by Brackett (1988a
and 1990). Three carrots were cut aseptically into pieces with sterile knives. Samples of
25 g were blended with 225 ml 0.1% peptone water (pH 7.0) in a stornacher for 3
minutes. The slurries were serially diluted in 9 ml 0.1% peptone water. To determine
populations of total aerobic microorganisms, duplicate samples were plated on plate
count agar (Oxoid CM463, and pH 7.0±0.2) and incubated at 30°C for 2 days. For the
estimation of E. coli and coliform population, duplicate samples were plated on violet
red bile agar (VBRA with MUG, Oxoid CM978) and incubated at 37°C for 1 day. To
determine moulds and yeasts, duplicate samples were plated on Rose-Bengal
Chloramphenicol Agar Base (Oxoid CM549) and incubated at room temperature for 3
57
Chapter 3. Carrot Storage (1 CC)
to 5 days. In all the cases pour plate methods were used. The mean log 100f viable
counts from two duplicate plates were noted .. Microbial populations were not analysed
immediately after disinfection, as they were assumed to be around OloglO CUF.g·1 as
was shown by Seyoum et al. (2003).
3.2.8. Subjective quality attributes
The descriptive quality attributes of carrots were carried out after 28 days of storage
at 1°C or room temperature according to the methods used by Ballantyne et al. (l988a
and b) and Brackett (1990). This descriptive quality attributes were determined
subjectively by observing the level of visible moulds growth, decay, shrivelling or
dehydration overall, as well as interior firmness and the surface appearance
characteristics such as smoothness and shininess of carrots. A rating with poor
(unmarketable), fair (some marketable), good (marketable), very good and excellent
was used (Mohammed et aI., 1999).
3.2.9. Experimental design and data analysis
A factorial experiment with 2 preharvest treatments, 3 prepackaging disinfecting
treatments, 2 storage temperatures and 3 replications were used in the study. The
experimental design was arranged in a factorial type of randomised complete block
design (RCBD), with three samples from each treatment combination. A pack of carrots
were taken randomly from each treatment group on each sampling day and used for the
different quality analyses. Each replicate sample for analysis of microbiological quality
and free sugar content (sucrose, glucose and fructose) was analysed in duplicate.
Statistical significant differences between the treatments were determined by analysis of
variance (ANOVA) with an MSTAT-C software package (MSTAT, Michigan State
Univ., East Lansing) and multiple comparison of the treatment means by Duncan's
multiple range test (Duncan, 1955). The effect of two different types of packaging films
with different levels of permeability to O2, CO2 and H20 vapour on microbiological,
physiological and chemical quality of stored carrots were investigated earlier (Seyoum,
et al., 2001). It was shown that an appropriate MAP improved the shelf life of carrots
58
Chapter 3. Carrot Storage (1 'C)
through controlling physiological activities such as allowing lower respiration rates,
prevention of condensation, but preventing moisture loss, maintaining optimum gas
composition and normal respiration of carrots without the occurrence of anaerobic
respiration during storage. Therefore, during the current investigation the statistical
analysis of the disinfecting treatment was coupled with MAP in order to see the overall
effect of these treatments on the quality parameters. The individual effect of MAP and
disinfecting treatments was analysed using multiple comparison of each treatment
means by mean separation of Duncan's multiple range test.
3.3. Results
3.3.1. Headspace gas concentration
Storage temperature had the greatest effect on changes in headspace gas
concentration (Fig. 3.1, 3.2 and 3.3). There was a significant difference (P :s 0.001) in
O2 consumption between carrots stored at 1°C and ambient temperature during the 32
days of storage. During the first 3 days, the O2 level decreased faster in packages of
carrots stored under room temperature than in the packages of carrots stored at 1°C.
After 3 days of storage at both temperatures, the O2 concentrations remained near
equilibrium i.e. 19%-20% at 1°C and 17.5%-18.5% at room temperature. The effect of
storage temperature on the headspace C02 concentration was also significant (P :s
0.001). The CO2 level increased rapidly in packages of carrots stored at room
temperature during the first 9 days. In the packages of carrots stored at 1°C, the CO2
increased the first 3 to 5 days, and then decreased slightly to stabilise after 9 days. The
CO2 ,level equilibrated after 9 days, i.e. below 1% at 1° and 2%-4% at room
temperature. Storage temperature was also an important factor affecting N2
concentration. The headspace N2 concentration was significantly (P :s 0.001) affected
with the storage temperature. The N2 levels increased during the first 3 days with a rapid
rise in packages of carrots stored at room temperature and equilibrated after 3 days, i.e.
at 80%-81 % at 1°C and 81.5%-82.5% at room temperature.
59
Chapter 3. Cerrot Storage (1 'C)
24 -,------------------------------------------------,
~comCat. Chlorinated, MAP, IOC --ComCat,Anolyte, MAP. IOC
23 ___"'_ComCat, Water, MAP, IOC ----*- Control, Chlorinated, MAP, IOC
_____ Control, Anolyte. MAP, IOC -----Control Water, MAP. IOC
22 ---+-- ComCat, Chlorinated. MAP, RT ... 0 ... ComCat, Anolyte, MAP. RT_. ~. - ComCat. Water. MAP, RT ... 0. .. Control Chlorinated, MAP, RT
~
.. ·0···Control, Anolyte, MAP, RT .. ·6···Control Water. MAP, RT
~=21.Q
~
le::l 20 .
(\)
CJ
§ 19
CJ
~=? 18 -
o
17 - ···.. ··6··
16
IS ~----~~----~------------------------------------
o 5 10 IS 20 25 30 35
Storage time (Days)
Figure 3.1. Changes in O2 content (%) in packages of carrots in Xtend® film stored at
1°C and room temperature (RT) for 32 days (n = 3 over six storage times).
Significance level showing the effect of pre- and postharvest treatment on O2
concentrations
Significance
Preharvest treatment (A) NS
Disinfecting (B) NS
Storage temperature (C) ***
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, *** Nonsignificant or significant at P ~ 0.01,0.05 or 0.001 respectively. LSDo.osValue = 0.378, S.E.
= 0.024 and e.V. = 0.035.
60
Chapter 3. Carrot Storage (1 CC)
6 -,----------------------------------------------------,
~ComCat. Chlorinated, MAP, IOC ____ CornCat, Anolyte, MAP, 1°C
--.-ComCat. Water. MAP. IOC ~Control. Chlorinated, MAP, IOC
---ilE--Control, Anolyie, MAP, IOC ---Control, Water, MAP, IOC
5 --+-- ComCat, Chlorinated, MAP, RT - - -0- - - ComCat, Anolvte. MAP. RT- -li< - - CornCat. Water. MAP. RT - - -<>- - - Control. Chlorinated. MAP. RT
- - -D- - - Control, Anolyte, MAP, RT - - -6- _. Control, Water, MAP_ RT
A
.'
)t.-.-'- -0-'-
" '0
'D
o ~----------------------------------------------------~
o 5 10 15 20 25 30 35
Storage time(days)
Figure 3.2. Changes in C02 content (%) in packages of carrots in Xtend® film stored at
1°C and room temperature (RT) for 32 days (n = 3 over six storage time).
Significance level showing the effect of pre- and postharvest treatment on C02
concentrations
Significance
Preharvest treatment (A) NS
Disinfecting (B) NS
Storage temperature (C) ***
AXB NS
AXC NS
BXC *
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P :$; 0.01, 0.05 or 0.001 respectively. LSDo,o5 Value =
0.826, S.E. = 0.074 and C.V. = 0.277.
61
Chapter 3. Carrot Storage (1 'C)
84 -
83 .0 .. '.
o . ". 0,-.., .'
0~ 82
'-'
e--
...9r..=o
..
81 -c
il)
CJ
C
0
CJ 80
c
il)
Ol)
0.... -+--ComCat, Chlorinated, MAP, IOC -----ComCat, Anolyte, MAP, IOC
.;:: 79 - __'_ComCat, Water, MAP, 1°C ----*-Control, Chlorinated, MAP, IOC
Z '* Control, Anolyte, MAP, IOC • Control, Water, MAP, IOC
-+--ComCat, Chlorinated, MAP, RT " .0 ... ComCat, Anolyte, MAP, RT
78 _.*.- ComCat, Water, MAP, RT ... o- .. Control, Chlorinated, MAP, RT
.. ·0···Control, Anolyte, MAP, RT " .6,... Control, Water, MAP, RT
77
0 5 10 15 20 25 30 35
Storage time (Days)
Figure 3.3. Changes in N2 content (%) in packages of carrots in Xtend® film stored at
1°C and room temperature (RT) for 32 days (n = 3 over six storage time).
Significance level showing the effect of pre- and postharvest treatment on N2
concentrations
Significance
Preharvest treatment (A) NS
Disinfecting (B) NS
Storage temperature (C) ***
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P :5 0.01, 0.05 or 0.001 respectively. LSDO.05 Value =
1.068, S.E. = 0.059 and C.V. = 0.081.
62
Chapter 3. Carrot Storage (1 'C)
The effect of preharvest ComCat® treatment on changes in 02, C02 and N2
concentrations in the packages of carrots was not significant (P ~ 0.05). Since these
results are indicative of the levels of respiration rate in carrots, they show that ComCat®
treated carrots had the same respiration rate as the controls. No significant difference (P
> 0.05) in changes of nitrogen concentration were observed in packages of carrots with
respect to preharvest treatments. For all three gases, a greater fluctuation after
equilibration was observed at room temperature, compared to storage at 1°C. There
were no significant differences in gas concentrations inside packages of carrots treated
with chlorinated and anolyte water. The effect of chlorinated and anolyte water dipping
and water wash treatments was not significant (P > 0.05) on gas concentrations during
the storage period. The interactive effect of disinfecting with storage temperature had a
significant (P :s 0.05) influence on the changes in the level of C02 during storage.
3.3.2. Physiological weight loss (PWL)
Table 3.1 shows PWL of carrots during the storage period of 50 days. Compared to
packaged carrots, the PWL was 22.3% higher in unpackaged ComCat® treated carrots
and 30.1% in control carrots stored at ambient temperature during the first two weeks
(Table 3.1). Signs of dehydration, such as a dull, shrivelled appearance, were the first
observable defects in unpackaged carrots. During 50 days storage, the PWL was in
general slightly higher in control carrots than in ComCat® treated carrots stored at 1°C.
This difference was not significant at P > 0.05, but at P s 0.07, and could show an
advantage of ComCat® over the control carrots.
Compared to the water washed carrots, the pooled mean PWL was found to be more
by 2.1% and 1.3% when dipped in chlorinated and anolyte water, respectively. In
several samples, the PWL was higher (P :s; 0.09) in chlorine washed carrots, compared
to anolyte disinfected ones.
63
Chapter 3. Carrot Storage (1 'C)
Table 3.1. Changes in physiological weight loss of carrots subjected to pre- and postharvest
treatments and stored at 1°C and room temperature (RT) for 50 days.
Physiological loss in weight (%)
Treatment day 7 day 14 day 21 day 28 day 35 day42 day 50
ComCat®, er, MAP, 1°C 3.132cd 5.036 de 6.385 c 8.889 cd 13.520C 17.520de 22.832 c
ComCat®, Anolyte, MAP, 1°C 2.717 d 5.624 de 7.112c 8.998 cd 14.504c 16.592 fg 21.958 ed
Comêat", ei, MAP, RT 10.226b 12.772c 22.256b 32.079b 48.412a 53.087 ab 57.559ab
ComCat®, Anolyte, MAP, RT 10.342b 14.585 c 20.130b 32.919b 44.098 b 51.016bc 54.906 bcd
ComCat®, H20, MAP, 1°C 2.486 d 3.446 de 6.095 cd 8.548 cd 14.265c 15.987gb 21.327 ede
ComCat®, H20, MAP, RT 9.107 bc 12.610 c 20.534 b 29.193b 44.444 b 49.675 c 55.498 abc
ComCat®,H o2O,l C 10.676b 27.667d 38.503 a 46.760a
ComCat®, H20, RT 21.363 a 34.881 b
Control, ei,MAP, 1°C 2.178 d 6.182d 7.312c IO.167c 15.001c 17.893 d 23.672c
Control, Anolyte, MAP, 1°C 4.818bcd 5.518 d 7.322 c 9.282 c 12.118c 16.211 gh 20.777cdef
Control, C12, MAP, RT 9.899 b 12.173 c 21.525 b 30.524b 45.696ab 54.282 a 57.965 ab
Control, Anolyte, MAP, RT 11.239b 12.229 c 22.683 b 28.022b 49.144 8 51.196 be 55.863 bc
Control, H20, MAP, 1°C 1.716d 5.282 d 7.114 c 9.098 ed 13.378c 17.211 ef 21.566 ede
Control, H 0, MAP, RT 7.939bcd2 12.944 c 20.889 b 27.941 b 45.7278b 51.094 bc 58.431 a
Control, H20, 1°C 10.657b 34.058b 37.259 a 43.837 a
Control, H20, RT 25.766" 43.037 a
Significance
Preharvest treatment (A) NS
Disinfecting + MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC **
BXC ***
AXBXC ***
NS, •• , *** Nonsignificant or significant at P~ 0.01 or 0.001 respectively. Means within a column followed by the same
letter(s) are not significantly different according to Duncari's multiple range test (P < 0.05). The LSD Value = 5.536, S.E. =
0.613. MSE = 11.829 and C.V. = 0.121.
64
Chapter 3. Carrot Storage (1 'C)
The storage temperature affected the PWL of carrots significantly (P < 0.001). After
50 days, the losses were found to be 36.9% and 34.2% more from packages of water
washed control and ComCat® treated carrots stored at room temperature than from
packages of water washed control and ComCat® treated carrots stored at 1°C,
respectively. Based on the group of postharvest treatments, the rate of PWL was divided
into three groups (Table 3.1). The highest moisture loss was from unpackaged carrots
stored at room temperature with the lowest rate of moisture transfer from packaged
carrots stored at 1°C. The three-way interaction between preharvest, disinfecting +
MAP and storage temperature treatments was highly significant (P ~ 0.001) on the PWL
of carrots.
3.3.3. Chemical changes
3.3.3.1. Total soluble solid (TSS)
Table 3.2 displays the changes in TSS of carrots subjected to different pre- and
postharvest treatments. The TSS significantly increased (P ~ 0.001) with storage time in
all samples (Appendix A.l). The TSS content of carrots raised with increased storage
temperature as well as with storage time. Individually, MAP highly influenced the
changes in the TSS contents (P ~ 0.001) of carrots stored at 1°C as well as room
temperature. The TSS of carrots increased at a lower rate in packaged carrots when
compared to the rates of increase of TSS in unpackaged carrots. Storage temperature
also had a highly significant (P ~ 0.001) effect on the changes in TSS content of carrots
during storage. As shown in Table 3.2, the TSS content increased faster and to higher
levels in carrots stored at room temperature than at 1°C.
At harvest the ComCat® treated carrots had a higher TSS than control carrots,
however, the difference was not significant (P ~ 0.05). A general trend of higher TSS
was also observed in ComCat® treated carrots compared to control carrots during 28
days of storage. It might therefore not be excluded that ComCat® treated carrots are of
better chemical quality than untreated ones.
65
Chapter 3. Carrot Storage (1 CC)
Table 3.2. Changes in total soluble solid (TSS) of carrots subjected to both pre- and
postharvest treatment and stored at 1°C and room temperature for 28 days.
Total soluble solid TSS (OBrix)
Treatment DayO day 14 day 21 day 28
ComCat®, C12, MAP, 1°C 9.267 a 9.200 ef 9.917 cd 9.667 f
ComCat®, Anolyte, MAP, 1°C 9.267 a 9.533 ef 9.200 de 9.333 fg
ComCat®, ei, MAP, RT 9.267 a 10.400 cd 10.667 be 12.133 abc
ComCat®, Anolyte, MAP, RT 9.267 a 10.200 cd 10.800 b 12.500 ab
ComCat®, H20, MAP, 1°C 9.267a 9.467 ef 8.933 de 9.533 f
ComCat®, H20, MAP, RT 9.267 a 9.933 ede 10.067 bed 11.267 cd
CorrrCat", H20, 1°C 9.267 a 10.433 cd 11.033 ab 11.633 be
Cornf'at'", H20, RT 9.267a 12.867 a
Control, ei,MAP, 1°C 8.800 ab 9.200 ef 9.500 ed 9.657 f
Control, Anolyte, MAP, 1°C 8.800 ab 9.268 ef 8.867 de 9.800 f
Control, Cb, MAP, RT 8.800 ab 10.267 ed 10.133 bed 11.333 be
Control, Anolyte, MAP, RT 8.800 ab 9.567 ef 10.600 be 11.500 be
Control, H20, MAP, 1°C 8.800 ab 9.133 ef 9.400 ed 9.333 fg
Control, H20, MAP, RT 8.800 ab 9.934 ede 10.233 bed 10.767 ede
Control, H20, 1°C 8.800 ab 12.267 ab 12.000 a 13.133 a
Control, H20, RT 8.800 ab 12.467ab
Significance
Preharvest Treatment (A) NS
Disinfecting +MAP (B) ***
Storage Temperature (C) ***
AXB NS
AXC **
BXC NS
AXBXC NS
NS, **, *** Nonsignificant or significant at P::; 0.01 or 0.001 respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range
test (P < 0.05). The LSD Value = 1.104, S.E. = 0.133, MSE = 0.466 and C.V. = 0.067.
66
Chapter 3. Carrot Storage (1 'C)
During 21 days at 1°C, the ComCat® treated carrots dipped in anolyte water had a
higher TSS content, when compared to the TSS content of control carrots dipped in
anolyte water, although not significant at P :s 0.05 level. The ComCat® treated carrots
dipped in chlorinated water had a slightly higher TSS content compared to those in
control carrots treated with chlorine, although not significant at P < 0.05 significance
level. Similarly, the control carrots dipped in tap water had a slightly lower TSS
content, except during the third week of storage at 1°C when compared to the TSS
content of carrots dipped in the disinfectant. Surprisingly, the packaged ComCat®
treated carrots dipped both in anolyte as well as chlorinated water had consistently
higher TSS contents during the storage period of 28 days at room temperature, when
compared to the TSS content of packaged control carrots subjected to the same
postharvest treatment. Even if there was no significant difference (P > 0.05) between
TSS content of the ComCat® treated and untreated carrots, the data could possibly
indicate a difference in metabolic activities. The group mean differences in TSS of
ComCat® treated and untreated carrots were found to be 0.467, 0.228, 0.142, and 0.339
°Brix for 0,14,21 and 28 days of storage, respectively.
The multiple comparison test showed that the TSS did not differ significantly for the
individual effects of disinfecting with chlorine, anolyte water dipping and control (P >
0.05 for all treatments). The TSS content of carrots dipped in anolyte water seemed to
remain approximately constant and slightly lower than the TSS content of carrots
dipped in chlorinated water, especially during the first 10 days at both storage
temperatures. At room temperature, the TSS seemed to build up and become slightly
higher in carrots dipped in anolyte water, when compared with those dipped in
chlorinated water. However, a higher group mean TSS was observed in carrots dipped
in chlorinated water than in the other two treatments (water washed and anolyte
treatments). Relatively, the lowest group means TSS was found in water washed carrots.
The two-way interaction between preharvest ComCat® treatment and storage
temperature was significant (P :s 0.01) on the changes in TSS content of carrots during
67
Chapter 3. Carrot Storage (1 'C)
storage. The three-way interaction between preharvest ComCat® treatment, disinfecting
together with packaging and storage temperature was only significant at p ~ 0.096.
3.3.3.2. Total available carbohydrate (TAC)
The TAC significantly decreased (P ~ 0.001) during the storage time of all samples
from around 13 g. 100g·1 to as low as 8 g. IOOg·l. A rapid decrease in TAC was
observed within the first two weeks of storage, followed by a slow decrease thereafter
for most treatments (Table 3.3). The TAC content was better maintained in packaged
carrots during storage at room temperature, as well as at 1°C, during 28 days. However,
the difference in TAC between packaged and unpackaged carrots were not significant at
P ~ 0.05 during the entire storage interval. Even if there was no significant difference (P
> 0.05) in the TAC change during this short storage period, there were generally higher
concentrations of TAC in packaged carrots than in unpackaged carrots stored at 1°C as
well as room temperature.
Storage temperature significantly (P ~ 0.001) affected the TAC in carrots during
storage. For example, the ComCat® treated carrots dipped in chlorinated, anolyte and
tap water and stored at 1°C had 14.1%,4.6% and 14.2% higher TAC contents than the
ComCat® treated carrots subjected to the same disinfecting treatment but stored at room
temperature for 28 days. Similarly, after 28 days at 1°C, the TAC contents in control
carrots dipped in chlorinated, anolyte and tap water were respectively 15.1%, 14.3% and
21.3% higher compared to the control carrots subjected to the same disinfecting
treatment and stored at room temperature. As it was mentioned earlier in this section, a
rapid decrease of carbohydrate was observed right after harvest and during the first
week of storage at both temperatures. During the later weeks of storage the
carbohydrate concentrations decreased faster in carrot stored at room temperature due to
the effect of higher temperature on the metabolic processes.
68
Chapter 3. Carrot Storage (1 'C)
Table 3.3. Changes in total available carbohydrate contents of carrots subjected to both pre-
and postharvest treatments and stored at 1°C and room temperature (RT) for 28 days.
Total available carbohydrate (g. 100g-t FW)
Treatment day 0 day 7 day 14 day 21 day 28
ComCat®, ei, MAP, 1°C 13.880a 10.373 be 9.371 abc 9.663 ab 9.589a
Comï.at", Anolyte, MAP, 1°C 13.880 a 9.632 bed 9.334 abe 9.352 abed 9.288 ab
ComCat®, Ch, MAP, RT 13.880 a 10.714 be 9.81Oa 8.294 bed 8.236 abe
Cornf.at", Anolyte, MAP, RT 13.880 a 12.430 a 9.983 a 9.477 abe 8.858 abe
Comï.at", H20, MAP, 1°C 13.880 a 11.413 ab 9.925 a 9.295 abe 9.277 ab
ComCat ®, H20, MAP, RT 13.880a 10.105 bed 9.597 ab 8.280 bed 7.957e
ComCat®, H20, 1°C 13.880 a 9.594 be 9.127bed 8.193 def 8.994 abe
Cornï.at'", H20, RT 13.880a 9.597 be 9.568 ab
Control, Ch, MAP, 1°C 12.590 ab 9.810 bed 9.758 a 9.490 abe 9.192 ab
Control, Anolyte, MAP, 1°C 12.590 ab 10.432 be 9.608 ab 9.479 abc 9.341 ab
Control, Ch, MAP, RT 12.590 ab 8.940 ef 8.900 bed 8.018def 7.803 e
Control, Anolyte, MAP, RT 12.590 ab 9.052 def 9.461 ab 7.929 ef 8.006 be
Control, H20, MAP, 1°C 12.590 ab 10.762 b 9.282 bed 9.837 a 9.518 a
Control, H20, MAP, RT 12.590 ab 9.553 cd 9.412 ab 8.256 bed 7.493 e
Control, H20, 1°C 12.590ab 10.479 be 9.934 a 9.428 abc 9.313 ab
Control, H20, RT 12.590ab 9.032 ef 8.927 bed
Significance
Preharvest Treatment (A) NS
Disinfecting +MAP (B) NS
Storage Temperature (C) ***
AXB *
AXC ***
BXC *
AXBXC *
NS, *, ***Significant at P $ 0.05 or 0.001 respectively. Means within a column followed by the same letter(s)
are not significantly different according to Duncan's multiple range test (P < 0.05). The LSD Value = 1.116,
S.E. = 0.127, MSE = 0.478 and e.v. = 0.069.
69
Chapter 3. Carrot Storage (1 'C)
The TAC content was slightly higher in ComCat® treated carrots at harvest and was
found to be 13.88 g. 100 g-I and 12.59 g 100 g-I for preharvest ComCat'" treated and
control carrots, respectively. The effect of preharvest treatment on the TAC during
storage of carrots was not significant at P :S 0.05, but at P :S 0.09 level. During the 28
days of storage at 1°C, there was a consistent trend in the changes of TAC content
between those concentrations in ComCat® treated and control carrots. The reason for
this may be maintenance of a kind of steady state in TAC in both preharvest ComCat®
treated and untreated carrots, which could be attributed to the effect of low temperature.
The TAC content remained to be slightly higher in ComCat® treated carrots subjected to
different postharvest treatments during 28 days at room temperature, although not
significant at P > 0.05. The comparison of group means over the storage period of 28
days indicated that the mean TAC remained higher (by 0.062 g. g-l FW) in ComCat®
treated carrots than in control carrots. This may indicate that slightly less conversion of
carbohydrates to free sugars took place in ComCat® treated carrots. During the 28 days
of storage at room temperature, the TAC was found to be higher in ComCat® treated
carrots, when compared to those concentrations in control carrots.
A general trend (P < 0.05) of higher TAC content was found in water washed control
carrots stored at 1°C compared to carrots dipped in chlorinated and anolyte water,
except for the 14th day storage interval. Although there were some discrepancies, similar
trends were observed in the changes in TAC content of control carrots subjected to these
disinfecting treatments and stored at room temperature. The two-way interaction
between the ComCat® treatment and storage temperature had a highly significant (P <
0.001) influence on the changes in TAC during storage. These interactions indicate that
the ComCat® treatment had a positive effect on the changes in TAC content of carrots
stored at low temperatures. The three-way interaction between pre- and postharvest
treatments was also significant (P < 0.05) on the changes of TAC in carrots during
storage. Indicating a general synergistic effect of pre- and postharvest treatments on
TAC content.
70
Chapter 3. Carrot Storage (1 'C)
3.3.3.3. Free sugar
The contents of individual sugars (sucrose, glucose and fructose) in carrots stored at
1°C and ambient temperatures are presented in Table 3.4 (a), (b) and (c). The sucrose
content varied between 5.37 g.100-1g and 3.09 g.100-1g, and decreased during the first 1
to 2 weeks of storage, after which it increased up to 21 days of storage, and finally
decreased at 28 days.
At harvest, the glucose content was significantly lower in ComCat® treated than in
control carrots, while the fructose and sucrose contents were higher, however, not
significantly (P > 0.05). MAP seemed to have a greater effect on the sucrose content of
carrots during storage. After 14 days at room temperature, the unpackaged ComCat®
treated and control carrots had 18.2% and 12.9% less sucrose, respectively, when
compared with the sucrose contents in packaged ComCat® treated and control carrots.
In general, the sucrose contents remained higher in packaged carrots, compared to those
in unpackaged ones stored at room temperature. The sucrose content also decreased
faster in unpackaged carrots stored at room temperature than in carrots stored at 1"C.
During the fourth week of storage the concentration of sucrose decreased more in
control carrots stored at room temperature compared to those stored at 1°C. During
storage, the preharvest ComCat® treatment had no significant (P > 0.05) effect on
sucrose concentration in carrots. However, a general trend of slightly higher sucrose
contents in the ComCat® treated carrots was observed.
The trends in sucrose concentration in carrots dipped in chlorinated, anolyte and tap
water were complex, when these carrots were stored at optimum temperature of 1°C,
although the concentrations of sucrose was significantly lower (P :s 0.05) in water
washed carrots on the th and 28th days of storage interval (Table 3.4 (a)). Nevertheless,
these trends seemed more clear when carrots dipped in different disinfectants and stored
at room temperature were compared.
71
Chapter 3. Carrot Storage (1 'C)
Table 3.4. (a). Changes in sucrose content of carrots subjected to both pre-and postharvest
treatments and stored at 1°C and room temperature (RT) for 28 days.
Treatment Sucrose (g.IOO-lg)
day 0 day 7 day 14 day 21 Day28
ComCat®, ei, MAP, 1°C 5.370 a 4.254 bed 4.005 be 5.615 ab 5.004 abe
ComCat®, Anolyte, MAP, 1°C 5.370a 4.5IObed 4.446 abe 5.020 abe 4.630 bed
ComCat®, ei, MAP, RT 5.370 a 4.122 bed 4.376 abe 4.313 ed 4.068 ede
Cornf'at", Anolyte, MAP, RT 5.370a 5.373 a 4.123 be 4.887 be 4.890 ab
ComCat®, H20, MAP, 1°C 5.370 a 3.707 de 4.409 abe 5.334 abe 3.533 e
ComCat®, H20, MAP, RT 5.370a 3.726 ede 4.012 be 4.579 ed 3.974 de
Cornï.at'", H20, 1°C 5.370 a 3.987 ede 3.737ede 4.287 ede 3.330 e
Comf'at", H20, RT 5.370 a 3.088 e 3.494 de
Control, ei;MAP, 1°C 5.122 ab 4.955 ab 4.744 abe 5.141 abe 5.11Iab
Control, Anolyte, MAP, 1°C 5.122 ab 4.327 bed 3.985 be 4.489 ed 5.774 a
Control, ei; MAP, RT 5.122ab 4.764 abc 5.297 a 4.156 ede 4.202 ede
Control, Anolyte, MAP, RT 5.122 ab 4.054 ede 4.777 ab 3.913 ede 4.139 ede
Control, H20, MAP, 1°C 5.122 ab 3.791 de 4.063 be 5.968 a 4.885 ab
Control, H20, MAP, RT 5.122 ab 4.530 bed 4.462 abe 3.999 de 3.535 e
Control, H20, 1°C 5.122 ab 4.468 bed 4.285 be 4.683 ed 4.648 bed
Control, H20, RT 5.122 ab 3.278 e 3.652 de
Significance
Preharvest treatment (A) NS
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB **
AXC NS
BXC **
AXBXC NS
NS, .*, ••• Nonsignificant or significant at p~ 0.0 I or 0.00 I respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test (P
< 0.05). The LSD Value = 0.813, S.E. = 0.062, MSE = 0.254 and e.v. = 0.111.
72
Chapter 3. Carrot Storage (1 'C)
After 28 days at room temperature, the sucrose content was significantly higher (P :5
0.05) in ComCat® treated carrots dipped in anolyte water than when dipped in
chlorinated and tap water. After approximately 18 days of storage at 1°C the sucrose
contents in ComCat® treated carrots, dipped in chlorine supplemented water, dropped
below those in control carrots which were also dipped in chlorinated water. The sucrose
concentration remained significantly (P:5 0.05) higher (by 15.4% after 28 days) in
ComCat® treated carrots dipped in anolyte water and stored at room temperature,
compared to control carrots that received the same postharvest treatments up to 28 days.
During the first 2 weeks of storage at room temperature, sucrose concentrations
decreased faster in ComCat® treated carrots dipped in chlorine supplemented water or
water washed compared to those in control carrots subjected to the same postharvest
treatment. In general, the ComCat® treatment had a positive effect on the sucrose
content when coupled with anolyte water treatment after 2 weeks of storage at room
temperature, although the differences in sucrose concentration in ComCat® and control
carrots dipped in anolyte water was not significant (P > 0.05) on most of the storage
intervals (Table 3.4 (a)).
Although the glucose content was significantly lower (P :5 0.001), almost half, in
ComCat® treated carrots at harvest, it did not differ much from the controls after 28
days of storage (Table 3.4 (b)). A general pattern of an increase in glucose contents of
carrots was noticed during the first two to the third week of storage stating the obvious.
The fructose content followed a similar trend (Table 3.4 (c)).
The preharvest ComCat® treatment had a significant (P :5 0.01) effect on the changes
in concentrations of glucose in carrots at both storage temperatures (Table 3.4. (b) and
Appendix A.l). Closer inspection shows that the differences are mainly at harvest and
not so much during storage. During the first 21 days of storage, glucose concentrations
were higher in controls than in ComCat® treated carrots treated with chlorine and stored
at 1°C (Table 3.4 (b)).
73
Chapter 3. Carrot Storage (1 'C)
Table 3.4. (b). Changes in glucose content of carrots subjected to both pre-and
postharvest treatments and stored at 1°C and room temperature (RT) for 28 days.
Treatment Glucose (g. 100.1g)
day 0 day 7 day 14 da~ 21 day28
CorrrCat'", Ch, MAP, 1°C 0.635 b 0.960 bed 1.326 abe 2.758 a 1.084 ab
ComCat®, Anolyte, MAP, 1°C 0.635 b 1.198 bed 1.084 bed 1.778 be 1.118ab
ComCat", ei;MAP, RT 0.635 b 1.157 bed 1.303 abe 1.514 ede 0.921 ab
ComCat'", Anolyte, MAP, RT 0.635 b 1.019 bed 1.048 be 1.467 ede 0.870 be
ComCat®, H20, MAP, 1°C 0.635 b 0.834 ed 0.983 be 2.177 b 1.315 a
ComCat®, H20, MAP, RT 0.635 b 1.835 a 0.903 be 1.561 ed 0.959 ab
CornCat'", H20, 1°C 0.635 b 1.111 bed 1.082 bed 1.284 ede 1.434 a
ComCat ®,H20, RT 0.635 b 1.283 abe 1.147 bed -
Control, Ch, MAP, 1°C 1.134 a 1.227 abed 1.516 a 1.766 bed 1.026 ab
Control, Anolyte, MAP, 1°C 1.134 a 1.148 bed 1.270 abe 1.717 bed 1.241 a
Control, ei, MAP, RT 1.134 a 1.388 abe 1.324 abe 1.015 de 0.816 be
Control, Anolyte, MAP, RT 1.134 a 1.186 bed 1.385 abe 1.015 de 1.119 ab
Control, H20, MAP, 1°C 1.134 a 0.997 bed 1.260 abe 2.300 ab 0.966 ab
Control, H20, MAP, RT 1.134 a 1.448 ab 1.487 a 1.347 ede 1.027 ab
Control, H20, 1°C 1.134 a 1.067 bed 1.135 bed 1.809 be 1.186 a
Control, H20, RT 1.134 a 1.238abed 1.681 a
Significance
Preharvest treatment (A) **
Disinfecting +MAP (B) NS
Storage temperature (C) *
AXB NS
AXC NS
BXC *
AXBXC NS
NS, *, ** Nonsignificant or significant at P::; 0.05 or 0.01 respectively. Means within a column followed
by the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05).
The LSD Value = 0.497, S.E. = 0.010, MSE = 0.095 and C.V. = 0.253.
74
Chapter 3. Carrot Storage (1 'C)
The glucose content remained lower (except at 21 days interval) in ComCat®treated
carrots dipped in chlorine solution compared to untreated carrots subjected to the same
postharvest treatment and stored at room temperature. On the contrary, during the first
21 days at 1°C, the glucose consistently remained lower in water washed ComCat®
treated carrots when compared to those concentrations in untreated carrots. Although
some deviations were observed over some storage intervals, changes in glucose
followed similar patterns in carrots dipped in anolyte water and stored. at 1°C.
However, after 28 days of storage the concentrations of glucose seemed to drop faster in
the control carrots dipped in chlorinated and tap water than in ComCat® treated carrots
stored at both temperatures. In general, the glucose content seemed to remain slightly
lower during the first two weeks, and slightly higher during the third and fourth weeks
of storage in control carrots than in ComCat® treated carrots.
The glucose content was maintained better in disinfected carrots during storage at
1°C compared to those washed in distilled water. Changes in glucose content in
unpackaged carrots were not significantly different from packaged ones, and
disinfecting + MAP also had no significant (P > 0.05) effect on the glucose content of
carrots (Table 3.4 (b)). The results also show that the glucose content remained higher
in ComCat® treated carrots, which were dipped in chlorinated water compared to those
dipped in anolyte water during storage at both temperatures, except during the second
and forth weeks of storage at 1°C. The two-way interaction between disinfecting +
MAP and storage temperature had a significant influence on the changes in glucose
content of carrots during storage.
The fructose content also showed a general increase up to week three of storage,
followed by a decrease. The effect of ComCat® treatment on the changes in fructose
content of carrots was significant at P S 0.01. Initially, ComCat® treated carrots had a
lower fructose content compared to untreated carrots (P > 0.05) (Table 3.4 (c)). During
storage of 7 days at 1°C, the fructose content remained lower in ComCat® treated
carrots, but increased thereafter.
75
Chapter 3. Carrot Storage (1 CC)
Table 3.4. (c). Changes in fructose content of carrots subjected to both pre-and
postharvest treatments and stored at 1°C and room temperature (RT) for 28 days.
Treatment Fructose (g. IOO-Ig)
day 0 day 7 day 14 day 21 day 28
CorrrCat'", Ch, MAP, 1°C 0.573 ab 0.858 ed 1.117a 2.000a 0.975 abe
Cornf.at'", Anolyte, MAP, 1°C 0.573 ab 0.901 bed 0.925 abc 1.296 bed 0.951 abc
ComCat®, ei, MAP, RT 0.573 ab 0.786 ed 0.919 abe 1.045 def 0.692 be
ConrCat'", Anolyte, MAP, RT 0.573 ab 0.960 bed 0.805 be 1.028 def 0.618 e
Comï.at", H20, MAP, 1°C 0.573 ab 0.678 d 0.835 be 1.470 be 1.007 ab
CorrrCat'", H20, MAP, RT 0.573 ab 1.348 a 0.730 be 1.120 ede 0.717 be
ComCat®, H20, 1°C 0.573 ab 0.836 ed 0.766 be 0.952 efg 1.325 a
ComCat®, H20, RT 0.573 ab 1.094 abc 0.871 abc
Control, Ch, MAP, 1°C 0.895 a 0.946 bed 1.106 a 1.202 ede 0.863 be
Control, Anolyte, MAP, 1°C 0.895 a 0.921 bed 0.967 abe 1.302 bed 0.975 abc
Control, Ch, MAP, RT 0.895 a 1.009 be 0.877 abc 0.795 ef 0.566 e
Control, Anolyte, MAP, RT 0.895 a 0.896 bed 1.035 ab 0.831 ef 0.906 be
Control, H20, MAP, 1°C 0.895 a 0.877 ed 0.931 abe 1.622 b 0.852 be
Control, H20, MAP, RT 0.895 a 1.113 abe 1.065 ab 0.995 def 0.818be
Control, H20, 1°C 0.895 a 1.285 ab 0.901 abe 1.355 be 1.017 ab
Control, H20, RT 0.895 a 1.038 be 0.744 be
Significance
Preharvest treatment (A) **
Disinfecting +MAP (B) **
Storage temperature (C) ***
AXB *
AXC *
BXC **
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P ::; 0.05, 0.0 I or 0.00 I respectively. Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple
range test (P < 0.05). The LSD Value = 0.327, S.E. = 0.010, MSE = 0.041 and C.v . = 0.215.
Mostly packaging slightly reduced the rate of fructose reduction during the storage at
room temperature, compared to unpackaged carrots (Table 3.4 (c)). Disinfecting + MAP
had a significant (P ~ 0.01) effect on the changes in fructose content of ComCat® treated
76
Chapter 3. Carrot Storage (1 'C)
and untreated carrots stored at 1°C and room temperature. Storage temperature was one
of the dominant factors affecting the fructose concentration in carrots during storage (P
~ 0.001). The higher storage temperature increased the rate at which the sugars were
depleted in carrots during storage. A rapid decrease in fructose content, especially after
three weeks of storage, was evident from the data presented in Table 3.4 (c). During 21
days of storage at room temperature, the water washed control carrots had a higher
fructose content compared to disinfected ones. With storage at room temperature, the
water washed ComCat® treated carrots had a higher fructose content compared to the
disinfected ones except during the second week of storage. Although no great difference
was observed, fructose content remained higher in ComCat® treated disinfected carrots
during the first 14 days at 1°C, and seemed to remain approximately the same
thereafter.
3.3.3.4. Total soluble sugar
The total soluble sugar was calculated from the experimental sucrose, glucose and
fructose content of carrots (Table 3.5). At harvest the total sugar was found to be 6.58
and 7.15 g.l 00-1 g fresh weight for CorrrCat" treated and control carrots, respectively.
The preharvest ComCat® treatment had no significant (P ;:::0.05) effect on the total
soluble sugar during storage. The ComCat® treated carrots dipped in chlorine water had
a higher total soluble sugar from 2 weeks storage onwards at 1°C, when compared to
control carrots dipped in chlorine. The total soluble sugar remained to be lower in
packaged as well as unpackaged ComCat® treated, water washed carrots during 28 days
at 1°C, although not significant (p>0.05). During the first 7 days at room temperature,
the total soluble sugar was found in higher amounts in control carrots dipped in
chlorinated or distilled water compared to the total soluble sugar in ComCat® treated
carrots subjected to the same treatments. Thereafter, the concentration became higher in
ConrCat" treated carrots subjected to the same treatments.
77
Chapter 3. Carrot Storage (1 CC)
Table 3.5. Changes in total sugar content of carrots subjected to both pre-and postharvest
treatments and stored at 1°C and room temperature (RT) for 28 days.
Treatment Total soluble sugar {g.100-'g FW)
Da~O Day7 Day 14 Da~ 21 Day28
ComCat®, ei,MAP, 1°C 6.578ab 6.072 bed 6.448 bede 8.780 ab 7.064 abe
ComCat®, Anolyte, MAP, 1°C 6.578 ah 6.609 abed 6.598 bede 8.095 abe 6.699 bed
ComCat®, ei,MAP, RT 6.578 ab 6.065 bed 7.366 abe 6.872 ede 5.681 ed
ComCat®, Anolyte, MAP, RT 6.578 ab 7.353 a 7.498 a 7.383 bed 6.378 bed
Comf.at'", H20, MAP, 1°C 6.578 ab 5.219d 5.975 bede 6.524 ede 5.855 ed
ComCat®, H20, MAP, RT 6.578 ab 6.909 abe 7.197abe 7.260 bede 5.650 ed
ComCat®, H20, 1°C 6.578 ab 5.935 bed 6.454 bede 8.981 a 7.484 ab
ComCat'", H20, RT 6.578 ab 5.465 ed 6.221 bede
Control, ei;MAP, 1°C 7.151 a 7.128 ab 6.227 bede 8.109 abe 7.000 bed
Control, Anolyte, MAP, 1°C 7.151 a 6.396 bed 5.645 bede 7.509 be 7.989 a
Control, ei;MAP, RT 7.151a 7.162 ab 6.254 bede 5.966 de 5.584 ed
Control, Anolyte, MAP, RT 7.151 a 6.136 bed 7.014 bed 5.760 e 6.164 bed
Control, H20, MAP, 1°C 7.151 a 5.665 bed 5.585 ede 8.224 ab 6.703 abed
Control, H20, MAP, RT 7.151 a 7.091 ab 6.320 bede 6.341 de 5.380 d
Control, H20, 1°C 7.151 a 6.820 abed 5.512 de 7.847 be 6.851 abed
Control, H20, RT 7.151 a 5.554 ed 6.543 bede
Significance
Preharvest treatment (A) NS
Disinfecting +MAP (B) **
Storage temperature (C) ***
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, **, *** Nonsignificant or significant at P~ 0.0 I or 0.00 I respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test (P <
0.05). The LSD Value = 1.251, S.E. = 0.066, MSE = 0.741 and C.V. = 0.129.
78
Chapter 3. Carrot Storage (1 CC)
Disinfecting + MAP had a significant (P < 0.001) effect on the total soluble sugar.
The ComCat® treated carrots dipped in chlorinated or anolyte water had a higher total
soluble sugar content during 21 days at 1°C, when compared to those that were water
washed. Similarly, the total soluble sugar was better maintained in control carrots
dipped in chlorinated or anolyte water compared to water washed ones, both stored at
1°C for 28 days, except for the 21 days storage interval. The total soluble sugar in
ComCat® treated carrots dipped in anolyte water remained higher than those in
untreated carrots dipped in anolyte water and stored at 1°C up to the 21 days and room
temperature up to 28 days, being significant for the latter (P < 0.001). The effect of
MAP was positive on the changes in total soluble sugar of ComCat® treated carrots
stored at room temperature, but no clear trends were obtained.
The storage temperature was highly significant (P :s 0.001) on the changes in total
soluble sugar content of carrots during storage (Table 3.5). In general, the total soluble
sugar increased during storage at 1°C until 28 days, peaking at 21 days, whereas it
decreased during storage at room temperature. After 28 days of storage, the percentage
difference in total soluble sugar content in carrots stored at 1°C, as well as room
temperature, was greater in control carrots than in ComCat® treated carrots. After 28
days of storage at 1°C, the total soluble sugar was 19.6%,4.8% and 3.5% more in
packaged ComCat® treated carrots dipped in chlorinated, anolyte and tap water,
respectively, when compared to the ComCat® treated carrots subjected to the same
postharvest treatments, but stored at room temperature.
The unpackaged ComCat® treated carrots dipped in tap water had 3.6% more total
soluble sugar after 14 days of storage at 1°C compared to the concentrations of this
sugar in the unpackaged ComCat® treated carrots stored at room temperature. The
greatest difference in total soluble sugar (19.6%), due to the effect of storage
temperature, was found for ComCat® treated carrots dipped in chlorinated water. .
The packaged control carrots dipped in chlorinated, anolyte and tap water had
20.2%,22.8% and 19.7% more total soluble sugar at the end of the 28 days of storage at
79
Chapter 3. Carrot Storage (1 CC)
1°C compared to the concentrations of this sugar in control carrots subjected to the
same postharvest treatments and stored at room temperature. After the first 14 days of
storage at 1°C, the total soluble sugar was 19.7% more in unpackaged control carrots
dipped in tap water compared to the concentrations in unpackaged control carrots stored
at room temperature. Although these results are not significant, they indicated a
tendency that the greatest effect of storage temperature on tota1 soluble sugar content
during storage, was on control carrots, rather than ComCat® treated ones.
The total sugar content was not significantly (P > 0.05) influenced due to the
interaction between the preharvest ComCat® treatment and storage temperature. None
of the interactions between pre- and postharvest treatment had a significant influence on
the changes in total soluble sugar content of carrots during this short period of storage.
3.3.3.5. Sucrose-hexose ratio
At harvest, ComCat® treated carrots had a significantly (P :s 0.05) higher, a1most
double, sucrose-hexose (SH) ratio (Table 3.6). During storage the SH was a1so
significantly (P :s 0.05) affected by the preharvest ComCat® treatment. The interaction
between preharvest and postharvest disinfecting and MAP treatments had a significant
(P :s 0.05) effect on the changes in SH during storage. The two-way interaction between
the postharvest treatments was highly significant (P < 0.001) on the changes of SH
during storage.
3.3.3.6. Ascorbic acid content (AA)
The changes in ascorbic acid (AA) content of carrots in the course of storage were
highly dependent (P :s 0.001) on the storage temperatures (Table 3.7). As a general
trend, the AA content of carrots decreased during storage at both temperatures.
Although a general trend of decrease in AA of carrots was observed during storage at
1°C, the rate of reduction with the progression of storage time was not significant (P >
0.05) (Appendix Al).
80
Chapter 3. Carrot Storage (1 'C)
Table 3.6. Changes in sucrose-hexose ratio of carrots subjected to both pre-and
postharvest treatments and stored at 1°C and room temperature (RT) for 28 days.
Treatment Sucrose-hexose ratio
DayO Day7 Day 14 Day 21 Day28
ComCat®, ei, MAP, 1°C 4.445 a 2.351 abe 1.712 ede 1.266 c 2.496 abed
ComCat®, Anolyte, MAP, 1°C 4.445 a 2.158 bed 2.364 abe l.847 abe 2.237 ede
Comf'at'", ei; MAP, RT 4.445 a 2.124 bed 1.978 bede 1.684 be 2.612 abed
ComCat®, Anolyte, MAP, RT 4.445 a 2.714 a 2.378 bed 1.954 abe 3.357 a
ComCat®, H20, MAP, 1°C 4.445 a 2.478 ab 2.567 ab 1.510 be 1.856 ede
CorrrCat'", H20, MAP, RT 4.445 a 1.171e 2.599a 1.756 abc 2.399 ed
ComCat®, H20, 1°C 4.445 a 2.061 bede 2.137bed 2.100abe 1.720 de
ComCat®, H20, RT 4.445 a 1.298 de 1.746 ede
Control, ei, MAP, 1°C 2.525 b 2.276 abe 1.816 bede 1.742 be 2.709 abe
Control, Anolyte, MAP, 1°C 2.525 b 2.080 bed 1.852 bede 1.588 be 2.681 abe
Control, ei, MAP, RT 2.525 b 1.989 ede 2.415 abe 2.591 a 3.324 ab
Control, Anolyte, MAP, RT 2.525 b 1.944bede 1.989 bede 2.225 ab 2.069 ede
Control, H20, MAP, 1°C 2.525 b 2.132 bed 2.015 bede 1.578 be 2.712 abe
Control, H20, MAP, RT 2.525 b 1.769bede 1.795 bede 1.881 abe 2.356 ede
Control, H20, 1°C 2.525 b 1.899abede 2.146 bede 1.482 be 2.144 ede
Control, H20, RT 2.525 b 1.455ede 1.282 e
Significance
Preharvest treatment (A) *
Disinfecting + MAP (B) **
Storage temperature (C) NS
AXB *
AXC NS
BXC ***
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P ~ 0.05, 0.01 or 0.001 respectively. Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple
range test (P < 0.05). The LSD Value = 0.705, S.E. = 0.046, MSE = 0.191 and e.V. = 0.188.
81
Chapter 3. Carrot Storage (1 'C)
The other important factor that significantly affected (P S 0.05) the AA content of
carrots during storage, was disinfecting treatment (Table 3.7). The AA content of
carrots dipped in chlorinated water decreased and remained lower during the storage
period at both temperatures than in carrots dipped in anolyte water. The decrease in AA
content of carrots dipped in either chlorinated or anolyte water was higher during
storage at room temperature than at 1°C.
The AA of carrots was not significantly (P > 0.05) affected by the preharvest
ComCat® treatment during the storage period. The ComCat® treated carrots had
approximately 0.5 mg.IOO-lg more ascorbic acid at harvest than the control carrots,
suggesting that ComCat® treatment had a positive effect on the nutritional quality
characteristics in terms of AA content. Although not significant (P > 0.05), a general
trend of higher AA content was found in ComCat® treated carrots during the storage
period of 28 days at both storage temperatures. However, some deviations in carrots
dipped in chlorinated water and stored at room temperature were observed. The
interactive effect of pre- and postharvest treatment had no significant (P > 0.05)
influence on the changes in AA content of carrots (Table 3.7). Therefore, combining
pre- and postharvest treatment showed to have strong benefits to consumers in terms of
better nutritional value of carrots after storage.
3.3.3.7. Peroxidase activity (POX)
The activity of POX of carrots rapidly increased during the first one or two weeks of
storage (Figure 3.4). The POX was found to be lower in carrots stored at room
temperature during the first week of storage, when compared to the activities of POX in
carrots stored at 1°C at a significance level of P S 0.07. Hence, it seemed that carrots
stored at 1°C are suddenly exposed to different conditions than those in the soil,
resulting in more respiratory enzyme activity during the early adjustment period. After
one week of storage, the level of activities of POX seemed to equilibrate in carrots
stored at 1°C, while it continued to increase in the carrots stored at room temperature
82
Chapter 3. Carrot Storage (1 'C)
Table 3.7. Changes in ascorbic acid content (AA) of carrots subjected to both pre and
postharvest treatment and stored at 1°C and room temperature (RT) for 28 days.
Ascorbic acid content (mg.IOO-lg FW)
Treatment DayO day 7 Day 14 day 21 day28
ComCat®, ei, MAP, 1°C 10.512 a 10.137 a 9.761 a 8.447 abc 9.011 ab
ComCat®, Anolyte, MAP, 1°C 10.512a 9.855 a 9.949 a 9.386 a 9.574 a
Comf.at", Cb, MAP, RT 10.512a 7.959 ede 7.957 de 5.913 de 3.942 de
Co~Cat®, Anolyte, MAP, RT 10.512a 9.496 ab 9.386 ab 7.040 be 4.224 d
Control, Ch, MAP, 1°C 9.574 ab 9.198 ab 9.157 ab 8.072 bed 7.884 be
Control, Anolyte, MAP, 1°C 9.574 ab 9.715 a 8.729 ab 9.011 ab 8.823 ab
Control, Cl-, MAP , RT 9.574 ab 8.447 bed 8.443 cd 6.180ede 2.816 e
Control, Anolyte, MAP, RT 9.574 ab 8.898 ab 8.635 ab 6.814 cd 4.029 d
Significance
Preharvest Treatment (A) NS
Disinfecting (B) *
Storage Temperature (C) ***
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, *, *** Nonsignificant or significant at P ~ 0.05 or 0.001 respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test (P
< 0.05). The LSD Value = 2.065, S.E. = 0.252, MSE = 1.610 and C.V. = 0.150.
until. two weeks of storage. Generally, the overall effect of storage temperature was
highly significant (P < 0.001) on the changes in levels of POX of carrots during the
third and fourth weeks of storage. The higher levels of POX in carrots stored at room
temperature could indicate the increased oxidation status of the carrots compared to
those stored at 1°C. In fact, the level of POX seemed to equilibrate in carrots stored at
1°C after one week of storage, and could be responsible for the protection of cell walls
and normal respiration and metabolism during the long-term storage of carrots at this
83
Chapter 3. Carrot Storage (1 'C)
temperature. The level of activities of POX in carrots was not significantly (P > 0.05)
affected due to the interactive effect between pre- and postharvest treatments with
storage temperature.
The data presented in Figure 3.4 clearly demonstrated the effect of pre-packaging
treatment (chlorinated or anolyte water) on the biochemical changes of carrots during
storage. The overall effect of disinfecting treatment on the level of POX in carrots was
significant (P :s 0.01). The level of POX was generally higher in carrots dipped in
chlorinated water, when compared to the POX in carrots dipped in anolyte water during
storage at both temperatures, at a significance level of P :s 0.09. At the end of day 7 at
room temperature, the POX in carrots was significantly (P :s 0.09) lower in carrots
dipped in anolyte water. After 28 days at 1°C the levels of POX were again significantly
lower in carrots dipped in anolyte water. The levels of POX in carrots were not
significantly (P > 0.05) affected by the preharvest ComCat® treatment both at harvest as
well as during storage.
The interactive effect of postharvest treatment with preharvest treatments was not
significant (P > 0.05) on the changes of the level of POX in carrots during storage. This
similarity in their biochemical changes could suggest that the shelf life of carrots treated
with ComCat® was as good as normal carrots at both temperatures. Polygalacturonase
activity was also tested for, but was not detected in carrots during storage, supporting
the previous findings reported by Stratilova et al. (1998).
84
Chapter 3. Carrot Storage (1 CC)
5 -
,.-._
:ws... .....~ .- .- .- .- .- .- .- .~ ,
'Ol) 4
:ê
r.r.i
..r0
3
o
'-'
:f 2 - ComCat, Chlorinated, MAP, IOCu --ComCat, Anolyte, MAP, IOCro ••• 0••• ComCat, Anolyte, MAP, RT
;>< ComCat, Chlorinated, MAP, RT
0
0... 1 Control, Chlorinated, MAP, IOC- '* Control, Anolyte, MAP, IOC••• !;J ••• Control, Anolyte, MAP, RT
_. ~. - Control, Chlorinated, MAP, RT
0
0 5 10 15 20 25 30
Storage tine (Days)
Figure 3.4. Changes in levels of activities of peroxidase in carrots subjected to different
pre- and postharvest treatments and stored at 1°C and room temperature (RT) for 28
days.
Significance level showing the effect of pre- and postharvest treatment on POX activity
Significance
Preharvest Treatment (A) NS
Disinfecting (B) **
Storage Temperature (C) ***
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, **, *** Nonsignificant or significant at P ~ 0.01 or 0.001 respectively. The LSDo.05 Value = 0.517,
S.E. = 0.063 and C.V. = 0.171.
85
Chapter 3. Carrot Storage (1 CC)
3.3.4. Microbiological changes
Storage temperature was one of the most important factors that significantly (P ::;
0.001) controlled the growth of microorganisms (Table 3.8). Total aerobic bacteria grew
and exceeded initial populations in packaged as well as unpackaged carrots stored at
room temperature. The overall treatment means for room temperature and 1°C storage
proved that cold storage was highly significant (P ::; 0.001) in controlling growth of
microorganisms. The populations of total aerobic bacteria in carrots stored at room
temperature was more than 40.5% higher after 28 days, than in carrots stored at 1°C.
The unpackaged carrots allowed greater growth of total aerobic bacteria during
storage at 1°C, except for the 14th day storage interval for control carrots, although this
was not significant (P > 0.05). However, packaging allowed significantly (P ::; 0.05).
greater growth of total aerobic bacteria in control carrots when stored at room
temperature. In general, this showed that MAP helped to control the aerobic bacteria
during storage of carrots at 1°C. The population of total aerobic bacteria remained
higher (by 7.0% after 14 days) in packaged control carrots stored at room temperature,
than in storage without packaging.
The effect of disinfecting and MAP treatment was highly significant (P ::; 0.001) on
reduction of aerobic bacteria on carrots during storage. The chlorinated and anolyte
water significantly (P ::; 0.001) reduced the populations of aerobic bacteria in carrots
stored at both temperatures in comparison with the populations of these microorganisms
associated with water washed carrots. The populations of aerobic bacteria decreased in
carrots dipped in chlorinated and anolyte water during storage at 1°C and did not exceed
initial populations at this temperature. The efficacy of chlorinated water on the killing
and suppression of the growth of total aerobic bacteria was not significantly (P ~ 0.05)
different from that of anolyte water as a disinfectant (Table 3.8).
Although not significant (P > 0.05), the populations of aerobic bacteria were slightly,
3.5%, higher in control samples than in ComCat® treated carrots at harvest. However,
the ComCat® treatment had a significant (P S 0.05) effect on the total aerobic bacteria
86
Chapter 3. Carrot Storage (1 'C)
Table 3.8. Total aerobic bacteria populations on carrots dipped in chlorinated and anolyte
water and storage at 1°C and room temperature (RT) for 28 days.
Total aerobic bacteria (log CFU.g-I FW)
Treatment DayO Day7 day 14 day 21 Day28
ComCat®, ei, MAP, 1°C 4.408 ab 2.07&k 1.544m 2.458 mno 2.513jkl
ComCat®, Anolyte, MAP, 1°C 4.408 ab 1.541 k 1.7241m 2.427 no 2.134 klm
ComCat®, Ch, MAP, RT 4.408 ab 3.604 h 4.832 def 5.659 cd 4.843 ef
Comf'at", Anolyte, MAP, RT 4.408 ab 4.131 gh 4.765 ef 5.372 e 4.796 f
Cornï.at'", H20, MAP, 1°C 4.408 ab 4.627 f 3.261 ghi 3.401 hijk 3.272 gh
ComCat®, H20, MAP, RT 4.408 ab 6.330a 6.073 ab 6.112 abc 5.942 abc
CornCat'", H20, 1°C 4.408 ab 4.942 ef 3.371 ghi 3.601 hi 3.348 gh
Comf'at'", H20, RT 4.408 ab 6.328 a 6.251 ab
Control, Ch. MAP, 1°C 4.568 a 2.183 ij 1.993 ij 2.463 no 2.534jkl
Control, Anolyte, MAP, 1°C 4.568 a 1.954jk 2.065 ij 2.540 no 2.865 ijk
Control, ei, MAP, RT 4.568 a 4.896 f 4.601 If 5.196 f 5.412 ede
Control, Anolyte, MAP, RT 4.568 a 4.363 gh 4.566 f 4.798 g 4.814 ef
Control, H20, MAP, 1°C 4.568 a 4.905 f 3.765 g 3.642 h 3.027 hij
Control, H20, MAP, RT 4.568 a 6.016 a 6.340a 6.618a 6.268 a
Control, H20, 1°C 4.568 a 5.468b cd 3.444 gh 3.738 h 3.397 gh
Control, H20, RT 4.568 a 5.291 ef 5.886 abc
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB **
AXC ***
BXC ***
AXBXC ***
*, **, *** Significant at P :s; 0.05, 0.0 I or 0.00 I respectively. Means within a column followed by the same
letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The LSD Value =
0.513, SE= 0.051, MSE = 0.101 and C.V. = 0.074.
87
Chapter 3. Carrot Storage (1 CC)
on carrots during storage. The numbers of viable aerobic bacteria was consistently
higher in the control carrots dipped in chlorine supplemented and anolyte water during
storage at 1°C, when compared to the populations of aerobic bacteria in ComCat®
treated carrots dipped in the same disinfectants. The populations of aerobic bacteria
remained to be lower in ComCat® treated carrots dipped in tap water during the first 16
days of storage at 1°C, after which the populations became approximately equal in both
CorrrCat" treated and control carrots, although not significantly different (P > 0.05). The
unpackaged ComCat® treated carrots had significantly (P :s 0.05) higher populations of
aerobic bacteria during 16 days compared to those in control carrots stored at room
tem perature.
The two-way interaction between ComCat® treatment and disinfecting + MAP was
highly significant (P ~ 0.001) on the changes of the populations of total aerobic bacteria.
Populations of total aerobic bacteria were also significantly (P ~ 0.001) influenced with
the interaction between ComCat® treatment and storage temperature. Similarly, the
interactive effect of postharvest treatments (disinfecting, MAP and storage temperature)
highly (P ~ 0.001) reduced the growth of aerobic bacteria during storage. The three-way
interactions of preharvest and postharvest treatment had a significant (P ~ 0.01) effect
on the changes in the populations of total aerobic bacteria in packages of carrots during
28 days of storage.
The population of moulds and yeast was also significantly (P ~ 0.001) affected with
storage temperature (Table 3.9). Higher storage temperature favoured growth of moulds
and yeasts on carrots. After 28 days at 1°C, there were 25% to 46.9% more populations
of moulds and yeasts in ComCat® treated and untreated carrots dipped in tap water and
stored at room temperature compared to those stored at 1°C, respectively. The number
of yeasts and moulds decreased much and remained lower after disinfecting when stored
at 1°C.
88
Chapter 3. Carrot Storage (1 'C)
Table 3.9. Changes in the population of yeasts and moulds in carrots subjected to
different disinfecting treatments and stored at 1°C and room temperature (RT) for 28
days.
Total Fungi Count (log CFU.g-J FW)
Treatment day 0 day 7 day 14 day 21 day 28
CornCat®, ei; MAP, 1°C 3.934 a 1.439 ghi 1.541 fg 1.673 fgh 1.831 efg
Comf'at", Anolyte, MAP, 1°C 3.934 a 1.511 ghi 1.424 g 1.634 gh 1.501 fg
CornCat®, ei, MAP, RT 3.934 a 3.093 de 3.26ge 3.431 abe 4.083 a
Comf'at'", Anolyte, MAP, RT 3.934 a 3.476 de 3.002 cd 3.244 be 3.473 be
Corn.Cat ®,H20, MAP, 1°C 3.934 a 2.322 f 3.052 ed 2.997 bed 2.855 cd
Comï.at'", H20, MAP, RT 3.934 a 3.988 bed 4.287 ab 4.120 a 3.823 ab
Comï.at", H20, 1°C 3.934a 2.818 ef 2.467 de 2.793 ede 2.475 de
ComCat ®,H20, RT 3.934a 5.589 a 4.488 a
Control, Ch, MAP, 1°C 3.866 a 0.952 i 1.842 fg 1.695 fgh 2.244 def
Control, Anolyte, MAP, 1°C 3.866 a 1.073 ghi 1.415 g 1.598 gh 2.179 def
Control, Ch, MAP, RT 3.866 a 2.580 ef 2.688 ede 3.886 ab 3.823 ab
Control, Anolyte, MAP, RT 3.866a 2.282 fg 2.678 ede 3.797 ab 3.637 ab
Control, H20, MAP, 1°C 3.866 a 2.077 fg 2.126 ef 2.167 efg 2.270 def
Control, H20, MAP, RT 3.866 a 4.228 be 4.118 ab 3.992 a 4.272 a
Control, H20, 1°C 3.866a 2.76gef 2.414 de 2.270 ef 3.078 bed
Control, H20, RT 3.866a 5.211 ab 4.148ab
Significance
Preharvest treatment (A) NS
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC *
BXC NS
AXBXC ***
NS, *, *** Nonsignificant or significant at P ::5: 0.05 or 0.001 respectively. Means within a column followed
by the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05).
The LSD Value = 0.633, SE= 0.053, MSE = 0.154 and C.V. = 0.126.
89
Chapter 3. Can-ot Storage (1 CC)
The numbers offungi were significantly (P ~ 0.001) affected with chlorinated and
anolyte water dipping treatments as compared to those in water washed controls.
Significantly (P ~ 0.001) higher numbers of yeast and mould populations were found in
water washed than in disinfected carrots when stored at 1°C temperature. The efficacy
of chlorinated and anolyte water in reducing the number of yeasts and moulds was not
significantly (P > 0.05) different during the storage period of 28 days. Yeast and mould
growth was not significantly (P > 0.05) affected by the preharvest ComCat® treatment.
The interactive effect of pre- and postharvest treatments significantly improved the
microbiological quality of carrots in terms of fewer populations of fungi. The three-way
interaction between all the pre- and postharvest treatments was highly significant (P ~
0.001) on the growth of fungi on carrots during storage.
The storage temperature greatly affected (P ~ 0.001) the populations of coliforms as
shown in Table 3.1O. Similar trends were obtained for control carrots during storage at
1°C as well as at room temperature. The results show that higher temperature storage
combined with MAP favoured more growth of coliforms in control carrots. MAP
coupled with cold storage temperature suppressed the growth of coliforms as compared
to storage at room temperature.
Although in most of the instances the populations of total coliforms in carrots
seemed to be lower in packaged carrots than in unpackaged carrots stored at 1°C and
room temperature, these trends were not consistent for all the treatments. Disinfecting +
MAP treatments resulted in a significant (P ~ 0.001) reduction of the populations of
total coliform bacteria. Treatment with chlorinated or anolyte water reduced (P ~ 0.001)
the numbers of coliforms compared to water washed carrots. After 28 days at 1°C, the
populations of coliform were significantly (P ~ 0.05) lower in carrots dipped in
chlorinated or anolyte water, when compared to water washed ones, but not in carrots
stored at room temperature.
90
Chapter 3. Carrot Storage (1 'C)
Table 3.10. Total coliform populations on carrots dipped in chlorinated and anolyte water
and storage at 1°C and room temperature (RT) for 28 days.
Total coliform bacteria (log CFU.g-1 FW)
Treatment day 0 day 7 Day 14 day 21 da~ 28
ComCat®, Ch, MAP, 1°C 3.400 ab 0.492 i 0.515 k 2.458 efg 1.700 ijk
ComCat®, Anolyte, MAP, 1°C 3.400 ab 1.798 gh 1.800 ij 2.427 efg 1.399 jk
ComCat®, ei; MAP, RT 3.400 ab 2.802 de 3.552 ed 2.573 defg 3.508 abed
ComCat®, Anolyte, MAP, RT 3.400 ab 2.725 de 2.728 efg 2.971 bede 3.024 bede
ComCat'", H20, MAP, 1°C 3.400 ab 3.255 ed 3.060 def 3.734 ab 2.722 defg
ComCat®, H20, MAP, RT 3.400 ab 3.517 be 3.491 de 3.870 a 4.150 a
ComCat, H20, 1°C 3.400 ab 3.321 ed 2.350 fgh 3.268 abed 3.348 bede
ComCat®, H20, RT 3.400 ab 3.996 ab 5.065 a
Control, ei,MAP, 1°C 3.449 a 1.837 fgh 1.989 ghi 2.463 efg 1.088 kl
Control, Anolyte, MAP, 1°C 3.449 a 1.994 fg 2.035 fgh 2.133 fgh 1.725 ijk
Control, ei;MAP, RT 3.449 a 2.198 efg 2.254 fgh 3.290 abed 3.492 abed
Control, Anolyte, MAP, RT 3.449 a 2.707 de 2.731 efg 3.941 a 3.256 bede
Control, H20, MAP, 1°C 3.449 a 3.167 ede 3.2l3 de 3.093 bede 2.785 edef
Control, H20, MAP, RT 3.449 a 4.305a 4.520 ab 4.217 a 3.691 abc
Control, H20, 1°C 3.449 a 3.964 ab 3.444 de 3.072 bede 3.304 bede
Control, H20, RT 3.449 a 4.128 a 4.225 ab
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC NS
BXC ***
AXBXC **
NS, *, **, *** Nonsignificant or significant at P ::;0.0 I, 0.05 or 0.00 I respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test (P <
0.05). The LSD Value = 0.740 S.E. = 0.049, MSE = 0.210 and e.V. = 0.147.
91
Chapter 3. Carrot Storage (1 CC)
As a general trend, populations of total aerobic and coliform bacteria remained lower
in disinfected ComCat® treated carrots in comparison with control carrots stored at 1°C
(P ~ 0.05). The interaction between postharvest treatments had a highly significant (P ~
0.001) influence on the reduction of growth of total coliforms.
The three-way interaction between pre- and postharvest treatments was highly
significant (P ~ 0.001) on the total coliform populations during storage. No viable E.
coli was found in anyone of the samples tested during the storage period.
3.3.5. Subjective quality attributes
The visual appearance observations on carrots are presented in Table 3.11. There
were distinctively different types of visual qualities, especially based upon the different
postharvest treatments and storage temperature. The appearance of carrots remained
excellent during the 4 weeks of storage at 1°C. The visual appearance of carrots was
highly affected by storage temperature. Visible mould growth and sprouting were
serious problems encountered with carrots stored at room temperature. These carrots
became dull with a firm surface with soft inner tissues. Carrots stored at 1°C
temperature remained firm, shiny and juicy during the 28 days of storage.
MAP improved the visual appearance of carrots during storage at 1°C, when
compared to the quality of unpack aged carrots (Table 3.11). The packaged carrots were
firm and shiny during storage at 1°C, while unpackaged carrots became soft and
bendable after a few weeks of storage at 1°C. It was noticed that the softening process
was faster in smaller carrots than in larger ones. Similarly, the visual appearance of
packaged carrots also remained better during storage at room temperature.
In open air there was excessive moisture loss, which resulted in dehydration and
shrivelling within a few days. Also, there was visible mould growth during the first few
days, which was soon slowed down due to dehydration of the carrots. MAP, when
combined with disinfecting treatment, improved the descriptive quality characteristics
of carrots during storage especially at 1°C (Table 3.11).
92
Chapter 3. Carrot Storage (1 CC)
Table 3.11. Changes in descriptive quality attributes of pre- and postharvest treated
carrots after 28 days of storage at 1°C and room temperature (RT).
Treatment Final state of carrots Rating
very shiny, firm and large size, very good
slightly etched
ComCat®, Anolyte, MAP, 1°C very shiny, firm and large size excellent
ComCat®, C12, MAP, RT most sprouting, rooting, slight mold, fair
etched, some dull, firm on surface,
some soft interior tissue
ComCat®, Anolyte, MAP, RT most sprouting, rooting, some dull, good
firm on surface, some soft interior
tissue
Comf'at'", H20, MAP, 1°C shiny, firm very good
ComCat®, H20, MAP, RT most sprouting, rooting, enhanced fair
mould growth, most dull, some
decay, firm on surface, some soft
interior tissue
CornCat", H20, 1°C some soft, marketable fair
Comf'at'", H20, RT moulds growth first, shrivelling, poor
some dried out, all unmarketable
Control, Ch. MAP, 1°C very shiny, some, firm and small very good
SIze
Control, Anolyte, MAP, 1°C very shiny, firm and small size, excellent
Control, Ch, MAP, RT most sprouting, rooting, slight mold, fair
etched, some dull, firm on surface,
some soft interior tissue
Control, Anolyte, MAP, RT most sprouting, rooting, some dull, good
firm on surface, some soft interior
tissue
Control, H20, MAP, 1°C shiny, firm, very good
Control, H20, MAP, RT most sprouting, rooting, enhanced fair
mould growth, most dull, some
decay, firm on surface, some soft
interior tissue
most soft, light and some fair
marketable
Control, H20, RT moulds growth first, excessively poor
shrivelling, most dried out, all
unmarketable
93
Chapter 3. Carrot Storage (1 'C)
, II
,j --
0 I
(" ) I
--_
I
I
(
i
,_ J \
\
I(nol~e '
I~~ _)5 min
2ór'nin i
'.
I t
-. , )
I ,\
j
.,:",;;.
.I~;~ j
;~,'~
I~r'
Figure 3.5. The effect of chlorinated and anolyte water dipping treatment on the visual
appearance of carrots stored at 1°C for 8 days (above) and 16 days (below), showing the
etched surface of the chlorine treated carrots.
94
Chapter 3. Carrot Storage (1 CC)
{j":" 'f
t- I -II 1/
~.'
'io,J .... ,
'4.Á....:.,.'."•-..c."
>;. '_ - ~
-{,
'·jA'notje
5" min "I
j !
.1' I
j , !
1
:I~ i
i, .- I
I'
,
.;
Figure 3.6. The effect of chlorinated and anolyte water dipping treatment on the visual
appearance of carrots stored at room temperature for 8 days (above) and 16 days
(below), showing the etched surface of the chlorine treated carrots.
95
Chapter 3. Carrot Storage (1 'C)
~;~
I ,/
J
I~- -~-l
Af\ol~te i
5mifl
Figure 3.7. The effect of chlorinated and anolyte water dipping treatment on the visual
appearance of carrots stored at room temperature for 30 days, showing the levels of
decay and moulds growth on the chlorine treated carrots.
96
Chapter 3. Carrot Storage (1 'C)
The anolyte water treatment coupled with MAP and low temperature storage
treatment showed the best visual appearance quality of carrots and was the optimum
operation for shelf life improvement of carrots. During storage at 1°C, carrots dipped in
anolyte water had a better visual appearance when compared to carrots dipped in
chlorinated water (Figure 3.5). The carrots dipped in chlorinated water for 20 minutes
had etched marks while the carrots dipped in anolyte water remained shiny and smooth.
The etching effect of chlorine on the surface tissue of carrots was more explicit when
stored at room temperature (Figure 3.6) compared to storage at 1°C (Figure 3.5). The
carrots dipped in anolyte water had no visual sign of decay after 30 days at room
temperature while carrots dipped in chlorinated water had signs of wet rot decay (Figure
3.7). Carrots dipped in anolyte water began to sprout one week earlier than the carrots
dipped in chlorinated water (Figure 3.6).
3.4. Discussions
The permeability and microperforations of the Xtend® packaging film used, allowed
sufficient O2 and CO2 concentrations in the headspace of packages of carrots, which was
enough to balance the normal respiration of carrots (Figure 3.1-3.3). The O2 and CO2
concentrations remained above 15% and below 5% during the storage period of 32
days, respectively, in packages of carrots (Figure 3.1 and 3.2). This is an indication for
normal respiration of carrots in microperforated film during storage without the
incidence of anaerobic metabolism (Exama et al., 1993), and was in the same order as
recommended by other researchers (Berg and Lentz, 1966; Phan, 1994). The ability of
this microperforated film to control the respiration gases (C02 and O2) established
within the sealed bags (Figure 3.1 and 3.2), maintained the freshness quality of carrots
(Table 3.11) without the incidence of anaerobic metabolism and decomposition, and is
in agreement with the views of Geeson (1988) who suggested suitable permeable plastic
film for the keeping quality of vegetables. At room temperature the Xtend® film did not
cause excessive depletion of O2 and accumulation of CO2, although the rate of
respiration of the carrots were higher (Wiley, 1994).
97
Chapter 3. Carrot Storage (1 'C)
The Xtend® film not only maintained optimum gas composition for normal
respiration but also reduced PWL from carrots during storage at both storage
temperatures (Figure 3.1), and no vapour condensation was observed. The unpackaged
carrots stored at room temperature lost the highest moisture content, while the lowest
rate of moisture transfer was observed for packaged carrots stored at 1°C. Similar
trends in changes in PWL from green chile stored at 8°C and 24°C were previously
reported by Wall and Berghage (1996). These data are in agreement with that of Kader
et al. (1989) and Jeon and Lee (1999). This has its own great advantage because the loss
of moisture of unpackaged carrots not only resulted in fruits and vegetable shrinkage,
dehydration and softening (Table 3.2 and 3.11), but triggers the other physiological and
biochemical processes (Table 3.4 and Figure 3.4), which was also shown by Ben-
Yehoshua (1967).
The TSS content of carrots was significantly (P :s 0.001) increased during storage
especially at room temperature (Table 3.2), which is in agreement with other research
(Lingaiah and Huddar, 1991; Jitender-Kumar et al.; 1999) that the TSS content of
carrots increases with the progression of storage duration, as well as storage
temperature. MAP significantly (P :s 0.05) affected the changes in TSS of carrots during
storage at 1°C as well as room temperature (Table 3.2). The increase in TSS of
unpackaged carrots was rapid, while the TSS content of packaged carrots was
maintained better during storage. The excessive increase in TSS of carrots during
storage is an indication of quality deterioration (Pal and Roy, 1988; Wasker et aI.,
1999). The changes in TSS content of carrots and the PWL had a direct relationship
during storage (Table 3.1 and 3.2). Such a correlation was reported earlier by Jitender-
Kumar et al. (1999), that the TSS increases with increasing PWL. The evidences
obtained that the TSS increased with the increase of PWL of carrots during storage
suggests the importance of reducing PWL through increasing storage air relative
humidity and by the use of MAP. The increase in TSS of carrots may partially result
from desiccation of carrots, which in turn leads to a concentrating effect on the TSS
98
Chapter 3. Carrot Storage (1 'C)
content. Since packaging prevented excessive moisture loss, the TSS content of carrots
was maintained better in samples stored at 1°C (Table 3.2).
The TAC content rapidly decreased within the first two weeks of storage (Table 3.3).
This decrease was reported to be due to the conversion of carbohydrates into free
sugars, such as sucrose, fructose and glucose (Nilsson, 1987; Suojala, 2000). Phan et al.
(1973) have shown that the changes in TAC content was due to the transfer of the
carrots from underground conditions to atmospheric environment, whereupon active
respiration takes place, which causes a demand for low molecule weight sugars, as is
discussed below for individual sugars. The TAC content of carrots was slightly lower (P
~ 0.05) in unpackaged than in packaged ones, especially towards the end of the storage
period (Table 3.3). In general, this result showed that MAP reduced the rate of
conversion of TAC into free sugars during storage at both temperatures, when compared
to unpackaged ones.
While the TAC decreased in packaged carrots, the sucrose content seemed to be
consistently higher in packaged carrots, while the glucose and fructose content showed
higher concentrations in unpackaged carrots during most of the storage intervals (Table
3.4 (a-c). These changes in carbohydrates can be explained by a higher metabolic
activity in unpackaged carrots with a subsequent hydrolysis of carbohydrates.
The excessive moisture loss in unpackaged carrots may also contribute to the
concentration of free sugars in unpackaged carrots (Table 3.1, 3.4 b and c). Similarly,
the total soluble sugar was found to be slightly higher in unpackaged carrots (Table 3.5)
while these carrots had a lower TAC content (Table 3.3). This data thus provides
evidence that there was more hydrolysis of carbohydrates, e.g. starch, into glucose and
fructose at higher rate than the amount of free sugar required for the glycolysis process
of the respiration pathway. Due to higher hexose sugar content and lower concentrations
of sucrose in unpackaged carrots, the SH generally remained lower in unpackaged
carrots (Table 3.6), which is in agreement with the results of Nil sson (1987) and Suojala
(2000), who reported that the SH sharply decreased during the early stages of storage.
99
Chapter 3. Carrot Storage (1 CC)
Conversely, Carlin et al. (1990) and Chervin and Boisseau (1994) reported that
sucrose, glucose and fructose rapidly decreased in minimally processed carrots, which
was mainly as a result of a high respiration rate due to wounds and losses of nutrients
(leakage) associated with this product. In the current results, as well as the data reported
by Nilsson (1987) and Suojala (2000), the SH seemed to equilibrate towards the later
storage period. This was because the fructose and glucose contents of carrots rapidly
increased during this period, while the sucrose content of carrots was decreased, mainly
during the early storage period. The SH of carrots stored both at 1°C as well as room
temperature, rapidly decreased during the first week of storage, and showed a general
decrease during the following two weeks. These results were in agreement with the
previous findings by Nilsson (1987) and Suojala (2000), who reported that the SH ratio
sharply decreased during the early stages of storage. In these results, as well as the data
reported by Nilsson (1987) and Suojala (2000), the SH seemed to equilibrate towards
the later storage period. This is because the fructose and glucose contents of carrots
rapidly increased during this period, while sucrose contents of carrots decreased,
especially during the first week of storage. The SH increased or equilibrated after three
weeks of storage, which was due to either an increase in sucrose, or a decrease in
fructose and glucose contents of carrots. The increasing effect of hexose on the total
sugar accumulation during the storage period was noticed. In general, the stabilisation
of SH after a few days of storage, could indicate that carrots need a self-adjustment time
after being dug from the soil, separated from leaves and exposed to the open air, before
finally having normal respiration and metabolism rates.
As a general trend, the total aerobic bacteria, and mould and yeast populations were
higher in unpackaged carrots during storage at 1°C (Table 3.8 and 3.9). The higher
glucose and fructose concentrations in unpackaged carrots (Table 3.4. b and c) could
partially contribute to higher populations of natural microbiological flora of control
carrots (Table 3.8 - 3.10). In packaged carrots stored at 1°C, the total aerobic bacteria
remained lower, which could partially be due to lower concentrations of glucose and
100
Chapter 3. Carrot Storage (1 CC)
fructose (Table 3.4 b and c) in these carrots, and the modified atmosphere created in the
headspace. For example, the microbial populations seemed to increase more during the
third week of storage in most of the samples, coinciding with the sudden increase in free
sugars in carrots during this storage interval (Table 3.4 and 3.8 - 3.10).
The visual appearance of unpackaged carrots highly deteriorated at room
temperature, when compared to packaged carrots (Table 3.11). During the early stages
of storage, due to availability of moisture and the favourable temperature, visible mould
growth occurred on unpackaged carrots, so that they were unmarketable after one week.
As the storage time advanced, the dehydration process seemed to stunt growth of
microorganisms and sprouting of unpackaged carrots. Loss of moisture was not a
problem in the packaged carrots during MAP storage at room temperature, however,
this resulted in sprouting of carrots. In general the results showed the benefits of MAP
to reduce physiological as well as biochemical changes and maintain the freshness
quality of carrots, and improving the effectiveness of other postharvest treatments such
as washing, disinfecting and low temperature storage, to improve the shelf life of
carrots.
Storage temperature was the most important factor that significantly (P ~ 0.001)
affected the postharvest quality of carrots (Table 3.1 - 3.11). The gas concentrations,
PWL, TSS, TAC, sucrose, fructose and glucose content, total aerobic bacteria, yeasts
and moulds and total coliform bacteria were significantly influenced by the storage
temperature. Varoguaux and Wiley (1994) showed that storage temperature highly
affects the physiology and biochemistry of vegetables, which was also demonstrated in
the current study, and resulted in significant physiological and biochemical changes in
carrots stored at room temperature (Table 3.1 - 3.11). Room temperature storage
increased the utilization of 02 and production of C02 by carrots compared to those
stored at 1°C, which, according to Wiley (1994), was due to the higher temperature
effect. The main physical change that occurred with carrots was loss of moisture, which
is one of the most important aspects related to fresh perishable vegetables that reduces
101
Chapter 3. Carrot Storage (1 CC)
the saleable weight and can induce senescence of the products (Grierson and Wardwski,
1978). The PWL was much higher in carrots stored at room temperature than in carrots
stored at 1°C. At room temperature the relative humidity of air usually is lower than the
vapour pressure exerted by water in the carrots, which creates vapour pressure
differences that are the deriving force for moisture movement outward (Salunkhe et al.,
1991; Ryall and Lipton, 1979). The surface tissue and skin of carrots seemed to be poor
barriers to moisture transfer from the flesh to the surrounding air. This results in a
higher rate of moisture transfer when stored at room temperature.
The AA content of carrots stored at 1°C as well as room temperature decreased
during storage (Table 3.7.). After two weeks of storage at room temperature, the
decrease of AA was much more in carrots stored at room temperature, which was due to
the interactive effect of storage temperature and storage time (P ~ 0.001) on the
physiology and biochemical activities of the carrots (Appendix A.!). Odebode and
Unachukwu (1997) reported that the AA in infected carrots decreased as the storage
period increased. With the microbiological flora as indicator of levels of infection of
carrots (Table 3.8 - 3.10), it may also be an explanation for the decrease in AA content.
Storage temperature was an important factor that had a highly significant (P ~ 0.001)
effect on the microbiological flora in carrots during storage (Table 3.8-3.10). The
microbiological qualities of carrots were better in carrots stored at 1°C, with
significantly (P ~ 0.001) lower populations of aerobic bacteria, moulds and yeasts, and
coliform bacteria. The reason for this could be attributed to several factors associated to
storage temperature. Apart from the physiological activity of microorganisms, the
physiological and biochemical changes in carrots are also reduced by the lower
temperature, which lead to slow respiration and metabolism of carrots. This in turn
resulted in the firm tissue that is resistant to microbial infection (Bracket, 1992). Higher
temperatures increased the hydrolysis of carbohydrates into free sugar (Table 3.3 and
3.4), and could lead to availability of nutrients for the microorganisms to grow (Table
3.8-3.10).
102
Chapter 3. Carrot Storage (1 'C)
Low temperature maintained the TSS content better in carrots during storage (Table
3.2). The rate of increase in TSS was rapid and significant (P S 0.001) at room
temperature compared to refrigerated storage. The TSS content increased faster and to
higher levels in carrots stored at room temperature than at 1°C (Pal and Roy, 1988;
Waskar et aL, 1999; Lingaiah and Huddar, 1991; Jitender-Kumar et al.; 1999). This
was partly attributed to higher moisture loss due to high temperature and low relative
humidity. Pal and Roy (1988) and Waskar et al (1999) reported similar trends on the
changes in the TSS during storage at different storage temperatures. Increased reduction
of TAC at room temperatures storage could be attributed to hydrolysis of carbohydrates
at a faster rate compared to storage at 1°C.
Since POX is a respiratory enzyme, the results show that the rates of oxidative
processes in the respiration increase during the first few days of storage. Berg and Lentz
(1966) and Phan et al. (1973) suggested that the rates of metabolic processes increase in
order to adjust the carrot roots to the new conditions immediately after they are
detached from the plant and exposed to environmental conditions that were different
from the underground conditions. The effect of storage temperature on POX activity of
carrots was significant (P S 0.05) during storage. The higher levels of POX in carrots
stored at room temperature during the later weeks of storage, could indicate the
increased oxidation status of the carrots, compared to those stored at 1°C. Similar to
MAP, storage temperature influenced the effectiveness of pre- and postharvest
treatments on keeping the qualities of carrots during storage, which was demonstrated
by the interactive effect of storage temperature with the other pre- and postharvest
treatments (Table 3.1 - 3.10). Low temperature storage supported the postharvest
washing, disinfecting and MAP towards the achievement of the improvement of shelf
life of ComCat® treated and untreated carrots. The coupled effect of MAP and storage
temperature seemed to have a synergistic effect on storage quality maintenance of
carrots. As mentioned above, MAP reduced O2 concentration in the headspace of
packages of carrots, and reduced the rate of respiration (Wiley, 1994), while low
103
Chapter 3. Carrot Storage (1 'C)
temperature reduces both biological and biochemical activities in the produce. In this
result, the combined effect of MAP and storage temperature significantly improved the
shelf life, as well as maintained better chemical, microbiological, and visual appearance
quality of carrots during storage (Table 3.1 - 3.11).
The prepackaging disinfecting of carrots in chlorine supplemented or anolyte water
significantly (P :S 0.001) reduced the populations of total aerobic bacteria, yeasts,
moulds and total coliform bacteria during storage (Table 3.8, 3.9 and 3.10). The results
of this study were in agreement with the previous work on efficacy of chlorine as a
postharvest decay control for vegetables (Zhuang et al., 1995; Velazquez et al., 1998;
Beuchat et al., 1998; Escudero et al., 1999; Beuchat et al., 2001; Ukuku and Sapers,
2001; Prusky et al. 2001;). The effectiveness of chlorine solution was highly dependent
on storage temperature with the most effective reduction of microbial populations
during storage being at low storage temperature (Table 3.8 - 3.10). The reason for this
is, that at low storage temperature, the deteriorative factors on carrots such as the
etching effect of chlorine on the absorbing surface tissue (Figure 3.5 and 3.6), the PWL
(Table 3.1) and chemical and biochemical changes (Figure 3.4 and Table 3.1-3.6), was
at a minimum and resulted in firm tissue, which is resistant to microbiological infection.
Once the natural microbiological flora of carrots was reduced by chlorine immediately
after disinfection, it remained lower at low temperature (Table 3.8 - 3.10). The results of
this chapter also showed that anolyte water significantly (P :S 0.001) reduced the natural
microbiological flora of carrots during storage. In general, anolyte water suppressed the
growth of microbiological flora throughout the storage period as good as chlorine, if not
better· (Figure 3.7 and Table 3.8 and 3.9). A short dipping time of 5 minutes in anolyte
water was found to be as effective as 20 minutes in chlorinated water on reducing and
retarding development of microbial flora on carrots during storage (Seyoum et aI.,
2003).
In comparison to carrots dipped in chlorinated water, the carrots dipped in anolyte
water displayed better fresh quality properties, such as a smooth and shiny surface, for
104
Chapter 3. Carrot Storage (1 'C)
one month of storage (Figure 3.5 - 3.7 and Table 3.11). Etching of the surface of carrots
by chlorinated water was observed, while carrots dipped in anolyte water remained
shiny and smooth (Figure 3.5). These results thus provide strong evidence that
chlorinated water may not be the optimum disinfecting treatment for carrots. An
alternative treatment is recommended, and anolyte water would be a good alternative.
The PWL was higher in carrots dipped in chlorinated water, when compared to those
dipped in anolyte and tap water. In a separate investigation, the difference was shown to
be significant (Seyoum et al., 2003). The higher loss of moisture from carrots dipped in
chlorinated water was attributed to its etching effect of this disinfectant on the absorbing
surface tissue of carrots (Figure 3.5 and 3.6).
The disinfecting treatment had no significant (P > 0.05) effect on the TAC, total
soluble sugar and glucose content of carrots during storage, however, the total soluble
sugars were better maintained in disinfected carrots. Disinfecting treatment had a
significant (P :s 0.05) effect on the reduction of AA (Table 3.7). The decrease of AA of
carrots dipped in chlorinated water was higher than that of anolyte washed samples
during storage at room temperature. The chlorinated water treatment also increased the
level of POX in carrots during storage. Again this could be due to the wounding effect
of chlorine on the surface tissue of carrots, resulting in increased metabolic activities
(Figure 3.4, 3.5 and 3.6) during storage. While both disinfectants showed to be similar
in effectiveness in killing and controlling postharvest decay during storage, these results
thus showed that disinfecting with anolyte water proved to be superior to chlorinated
water in maintaining the optimum physiological condition, nutritional value, as well as
some biochemical processes.
The interactive effect of disinfecting treatment + MAP and storage temperature was
significant on the changes in PWL (P :s 0.001), TAC (P :s 0.05), sucrose content (P :s
0.01), SH (P:S 0.001), total aerobic bacteria (P :s 0.001) and population of total
coliform bacteria (P :s 0.001). The best quality properties of carrots were maintained
due to the interactive effect between anolyte water disinfecting, use of MAP, and low
105
Chapter 3. Carrot Storage (1 'C)
temperature storage. Therefore, suitable combinations of preharvest practice,
prepackaging treatments, packaging and control of environmental factors should be
used to improve the quality and shelf life of packaged carrots.
The effect of preharvest ComCat® treatment on changes in oxygen, carbon dioxide
and nitrogen concentrations in the packages of carrots were not significant (P > 0.05).
These results are indicative of the levels of respiration rate in ComCat® treated and
control carrots, suggesting that ComCat® treated carrots have the same respiration rate
as the control. This similarity in their biochemical changes could then suggest that the
shelf life of carrots treated with ComCat® was as good as normal carrots at both
temperatures. Some of the results of this research showed that an improvement in some
quality properties of carrots could be achieved by preharvest ComCat® treatment. As a
general trend, the ComCat® treatment resulted in a reduction of the PWL of carrots
during storage. One of the reasons for the higher losses of moisture from control carrots
was their smaller size as compared with the size of ComCat® treated carrots, therefore
. having a relatively larger surface area for evaporation. The other reason could be
attributed to the effect of plant growth hormones in ComCaf", such as gibberellin and
auxin, which are known to reduce PWL in fruits and vegetables (Bartholomew et al.,
1983; Rodrigues and Subramanyam, 1966; Salunkhe, et al., 1975; Stallknecht et al.,
1983).
The TSS was slightly higher in ComCat® treated carrots compared to the controls
during storage, although only significant at P :s 0.09. The interesting point was, that in
most of the sampling intervals, the TSS values remained higher in ComCat® treated
carrots (Table 3.2). This pattern of TSS was consistent in the case of carrots stored in
MAP at 1°C as well as room temperature for 28 days, but not in unpackaged carrots.
The interactive effect of preharvest ComCat® treatment and storage temperature was
significant (P :s 0.01) on the changes in TSS content of carrots during storage. This
shows the necessity of proper storage temperature in order to maintain the TSS of fresh
harvest ComCat® treated carrots. The plant growth regulators in Comf'at'", such as
106
Chapter 3. Carrot Storage (1 'C)
gibberellin, indole-3-acetic acid and brassinosteroids, with their individual functions
during plant growth and development, seemed to have promote the accumulation of
TSS.
An increase in low molecular weight sugars during the early stages of storage of
carrots was previously reported by Phan et al., 1973, Nilsson, 1987 and Suojala, 2000.
These researches also showed that the hexose sugars increase in carrots during storage,
while the sucrose content decreases, and the total soluble sugar content seems to remain
constant with the progress of storage time. In this study, the data also showed an
increase in hexoses, with a simultaneous decrease of sucrose and TAC content during
storage (Table 3.3 and 3.4 a - c). However, in Table 3.4 (b) and (c), it can be seen that
the glucose and fructose contents are in the same order of magnitude as the respective
contents of control carrots at harvest. These results therefore do not agree with those of
Nilsson (1987) and Suojala (2000). However, the sugar contents do not decrease as
drastically as was reported by Carlin et al. (1990) and Chervin and Boisseau (1994) for
minimally processed carrots, where high respiration rates were observed due to
wounding and leakage losses of nutrients. The change of sugar contents in intact fresh
carrots during storage is lower, as compared to minimally processed carrots due to a
relatively lower metabolism rate during storage.
General trends of the sugar data showed that the plant growth hormones reduced (P :s
0.1) the hexose sugar content in ComCat® treated carrots (Table 3.4 and 3.5). The
previous investigation on the fruit composition as effected by preharvest gibberellin
treatment showed that this plant growth hormone resulted in lowering of both
hesperidine and reducing sugars (Salunkhe ef al., 1991). In this study the free sugars
such as glucose and fructose (Table 3.4 b and c) were found to be lower in CorrrCat'"
treated carrots at harvest, which may be attributed to the effect of the gibberellin in
ComCat®. A general trend of lower glucose and fructose content was observed in
ComCat® treated carrots during storage. The reason for this could be a lower rate of
conversion from polysaccharides to free sugars (sucrose, glucose and fructose), which
107
Chapter 3. Carrot Storage (1 CC)
in turn would indicate higher rates of metabolic activities before harvest. The preharvest
ComCat® treatment increased the TAC (P ~ 0.05), sucrose (P > 0.05) and TSS (P >
0.05) of carrots at harvest (Table 3.1, 3.3 and 3.4 (a)). This could indicate that ComCat®
increased the biosynthesis of polysaccharide carbohydrates while efficiently utilizing
free sugars for physiological processes during the growth and development period. A
previous investigation on the fruit composition as effected by preharvest gibberellin
treatment showed that this plant growth hormone resulted in lowering reducing sugar
content (Salunkhe ef al., 1991), which is confirmed by the present findings. This may
have its own advantage in keeping microbial population in carrots low in preharvest
ComCat® treated carrots during storage (Table 3.8 - 3.10), which was also observed in
lower populations of total aerobic bacteria, total coliform bacteria at harvest and during
storage, which seemed to have had a direct relationship with the contents of total
soluble sugar, glucose, fructose and sucrose contents of these carrots (Table 3.4 - 3.5
and Table 3.8 - 3.10). However, the relationship between the changes in sugar and the
population of microorganisms in ComCat® treated carrots was not consistent and more
complex, due to the other postharvest treatments applied.
When the carrots were stored at low temperature (1°C), TAC decreased to a steady
state after 14 days of storage. At room temperature the TAC remained consistently
higher in ComCat® treated carrots subjected to different postharvest treatments and
storage (Table 3.3). These data show that ComCat® treatment had a positive effect on
the maintenance of TAC in carrots stored at higher temperature, suggesting better
postharvest quality.
The interactive effect of ComCat® treatment and postharvest treatments significantly
(P ~ 0.05) influenced the PWL, TAC, and populations of microorganisms during
storage (Table 3.1, 3.3 and 3.8 - 3.10). The results suggested that the ComCat® treated
carrots, when combined with anolyte water dipping treatments and stored at the
optimum low temperature, would help to increase the shelf life. Three-way interactions
between the pre-and postharvest treatments were observed for the PWL (P ~ 0.001),
108
Chapter 3. Carrot Storage (1 'C)
TAC (P :S 0.05) populations of aerobic bacteria (P :S 0.001), fungi (P :S 0.001) and
coliform bacteria (P :S 0.01). In general, the chemical quality characteristics were also
maintained better in carrots subjected to proper combinations of postharvest treatments.
In summary, the results in this chapter showed that anolyte water dipping treatment
may be a better disinfectant treatment for carrots than chlorine, as it has shown that it
did not etch the surface tissues, significantly reduced the natural microbiological flora
and resulted in higher contents of TSS and AA, perhaps due to induced lower metabolic
rates, without affecting the other quality properties. Preharvest ComCat® treatment
improved some of the quality properties of carrots at harvest and during storage. The
advantages gained by the preharvest ComCat® treatment are:
1) higher TAC, TSS, AA, sucrose content and SH and lower populations of
total aerobic bacteria and total coliform bacteria at harvest, although only
significant at P :S 0.09.
2) better chemical quality characteristics during storage in terms of higher TSS
(P > 0.05) and lower PWL (P > 0.05) in ComCat® treated carrots during
storage at 1°C, although only significant (P :S 0.09)
3) better maintenance of TSS, AA and TAC in carrots during storage at room
temperature
4) improved keeping quality in relation to better visual appearance during
storage at 1°C
The findings that ComCat® treatment showed better maintenance of TSS, total
soluble sugar, TAC and AA in carrots at room temperature, would encourage research
on the performance of ComCat® treated carrots in evaporative cooling conditions at a
storage temperature higher than the optimum 1°C. The results of such research are
presented in chapter 5.
Carrots are a subsurface root part of a plant. The data obtained for carrots may
perhaps not be appropriate to predict the effect of preharvest ComCat® treatment on
biological and biochemical changes in other parts of plants, such as the fruit, during
109
Chapter 3. Carrot Storage (1 'C)
storage. For comparison, an investigation on the effect of preharvest ComCat® treatment
on biological and biochemical changes in a fruit was consequently carried out. In this
respect, the performance of ComCat® treated tomatoes during storage is presented in
chapter 4.
110
CHAPTER4
EFFECT ofPRE- and POSTHARVEST
TREATMENTS on PHYSIOLOGICAL, CHEMICAL
and MICROBIOLOGICAL QUALITIES of
TOMATOES
Abstract
Preharvest ComCat® treated tomatoes and untreated controls were evaluated for
changes in physiological, chemical and microbiological quality characteristics during
storage at l3°C and room temperature (16.9 - 25.2°C) and a relative humidity of 34 -
76% after 8, 16,24 and 30 days. The effectiveness of MAP in Xtend® film, disinfection
treatments with chlorine or anolyte water and different storage temperatures were also
evaluated. The 02 and CO2 concentrations remained above 15% and below 6% during
storage, respectively. MAP reduced' utilisation of free sugars, reduced moisture loss,
retained ascorbic acid (AA), and slightly suppressed growth of microorganism. Storage
temperature was the most dominant factor that affected all the quality parameters tested.
Faster ripening of tomatoes at room temperature was accompanied by rapid changes in
O2 and C02 and increased the physiological weight loss (PWL), pH, utilization of free
sugar, peroxidase (POX) and polygalacturonase (PG) activities, and populations of
microorganism.
Disinfecting treatments significantly reduced microorganisms. Chlorine disinfection
resulted in higher O2 consumption and CO2 production than anolyte water, implying
higher respiration and metabolism rates in these tomatoes. PWL was lower and the total
soluble solids (TSS) content, total soluble sugar, POX activity, and marketability of
tomatoes were generally maintained better in tomatoes dipped in anolyte water. The
fructose content increased continuously in tomatoes dipped in anolyte water for up to 24
days while fructose increased only up to 16 days in tomatoes dipped in chlorinated
III
Chapter4. Tomato Storage (13'C)
water during storage at 13°C. Disinfecting In anolyte water delayed senescence
slightly.
At harvest, ComCat® treated tomatoes had a lower pH, lower levels of ascorbic acid,
fructose and glucose, higher levels of TSS, total titratable acids (TTA) and sucrose,
higher POX activity, and lower microbial populations, than controls. ComCat®
treatment had a significant effect on O2 and N2 concentrations, PWL, pH, AA content,
sucrose content, POX activity, aerobic bacteria, moulds and yeasts, coliform bacteria
and marketability of tomatoes during storage. During storage at room temperature, the
headspace of packages of ComCat® treated tomatoes had higher O2, lower CO2 and
lower N2 contents, which indicated a lower respiration rate, compared to controls.
During storage the AA and TSS contents were better retained in ComCat® treated
tomatoes than in control tomatoes, while the sucrose and glucose contents stayed lower
in ComCat® treated tomatoes. However, after full ripeness, the fructose content was
higher in ComCat® treated tomatoes, compared to controls. The POX activity was
generally lower in ripening ComCat® treated tomatoes than in control tomatoes. The
difference in PG activity was only visible after 30 days at 13°C between the ComCat®
treated and control tomatoes. The climacteric peak of ripening was delayed almost by
one week in ComCat® treated tomatoes. Due to low concentrations of free sugar, high
TTA, low pH and high POX activity in ComCat® treated tomatoes, the microbial
populations were generally lower during the early stages of ripening in storage. Finally,
the marketability of ComCat® treated tomatoes were significantly better than that of the
control tomatoes, especially under room temperature storage conditions.
4.1. Introduction
Postharvest physiological, microbiological, chemical and biochemical qualities of
tomatoes partly depend upon preharvest factors such as genetic, climatic, biotic,
edaphic, chemical and hormonal factors, as well as combinations of these (Hobson,
112
Chapter 4. Tomato Storage (13 'C)
1988; Jauregui et al., 1999; Leonardi ef al., 2000; Prieto ef al., 1999;Salunkhe et al.,
1991; Shi et al., 1999).
Five major classes of plant hormones are generally recognised: auxin, gibberellin,
cytokinin, abscisic acid and ethylene (Davies, 1995; Mauseth, 1991; Raven et al., 1992;
Salisburg and Ross, 1992), which may change the rate of biological and biochemical
changes in fruits. To achieve a given objective postharvest research is necessary
whenever new plant growth regulators or other chemicals are externally applied during
growth and development, because the treatment could have positive or negative effects
on the quality of fruits at harvest and or during storage. ComCat® is a substance
extracted (see Chapter 1 and 2) from plants, and consists of combinations of plant
hormones (auxin, gibberellin, brassinosteroids, kinetins), aminoacids, natural
metabolites and other ingredients that were shown to increase the yield of vegetables
(Schnabl et al., 2001). However, there are no data available on the postharvest
physiology, microbiology, chemical and biochemical quality aspects of preharvest
ComCat® treated tomatoes.
The aims of postharvest treatment of fruit are to reduce enzymatic activities and
postharvest decay problems. Chemical treatments were found to be effective in reducing
the occurrence of postharvest decay by pathogens (Eckert, 1990; Barth et al., 1995;
Beuchat et al., 1998; Afek et aI., 1999, Prusky et aI., 2001) and hot water washing was
also found to be very efficient to control postharvest decay in fruits and vegetables
(Rodov et al., 1995; Fallik et al., 1999 and 2000). Most chemical treatments may leave
residues and consequently encounter consumer acceptance problems (Johnson and
Sangchote, 1994; Wisniewski and Wilson, 1992). This necessitates research in search of
alternative disinfecting treatments. Anolyte is a good candidate, and has been shown to
be effective in retarding growth and proliferation of microorganisms on carrots during
storage (Chapter 3).
113
Chapter 4. Tomato Storage (13 'C)
The objectives of this chapter were: (1) to investigate the postharvest properties of
ComCat® treated tomatoes; (2) to investigate anolyte water as an alternative disinfectant
to a chemical treatment such as chlorine to reduce microbial load and suppress their
growth thereafter during storage; and (3) to investigate the storage quality of preharvest
ComCat® treated tomatoes using MAP at 13°C and ambient temperature.
4.2. Materials and Methods
4.2.1. Tomato production
Tomatoes (Leucopersicon esculentum, var. Marglobe) were grown during the
autumn season in the area of Bloemfontein South Africa. ComCat® was applied at 109
ha-1 in 350 litres, and Og ha-1 as control, and was sprayed twice during the growth and
development of tomatoes. The first spraying was performed prior to transplanting of the
seedlings while the second spraying was at the start of flowering. The other preharvest
practices were kept constant between the treatments during production of tomatoes in
this experiment. Fruit were harvested manually at the green-mature stage and delivered
to the laboratory immediately after harvest. In order to protect the tomatoes from
mechanical injury during transportation, plastic crates were used. For each preharvest
treatment, the tomato fruit were harvested from four random blocks in order to obtain
representative samples. Fruit without observable mechanical injury, blemishes or
defects were selected for the study. The working surfaces and all tools used for
processing of tomatoes during disinfecting, packaging and storage were washed and
disinfected with I% Chlorobac (Syndachem, Pty, Ltd.) prior to use. Immediately after
delivery to the laboratory, the fruit were hand washed with water, to remove field heat,
surface dust and reduce microbial populations on the surface. Prepackaging disinfecting
. treatments and packaging oftomatoes were performed on thesame day.
4.2.2. Postharvest treatment
The postharvest disinfecting, packaging and storage treatments were conducted
according to the methods described in chapter 3, section 3.2.2. After washing a total
114
Chapter 4. Tomato Storage (13 'C)
amount of 144 kg ComCat® treated tomatoes were subdivided into three groups of 48
kg each in preparation for dipping treatments in chlorinated water, anolyte water and tap
water. Plastic containers were washed, disinfected and rinsed by distilled water prior to
use for the dipping treatments. Plastic containers were used to avoid losses of charged
ions from anolyte, which would be the case with metal containers. Tap water in plastic
containers was adjusted to IOO!J.g.mr' total chlorine with standard grade sodium
hypochlorite (5% NaOCI), in which tomatoes were dipped for 20 minutes.
The pH of anolyte water was adjusted to pH of 6.7 and contained 0.87% total
dissolved solids. Immediately after preparation, anolyte water was used for disinfecting
tomatoes for 5 minutes.
4.2.3. Modified Atmosphere Packaging
The tomatoes were subdivided into 1 kg-samples, which were packed in commercial
micro-perforated bags (Xtend® Film, Patent No. 6190710, StePac L.A., Ltd., Israel),
which are specifically designed for tomato packaging and for storage at 13°C. The
unpackaged 1 kg-sample tomato, for each treatment combination, were placed on
perforated plastic bags and left open during storage at 13°C or room temperatures.
Tomatoes were stored at 13°C and RH of 34-76% and at room temperature (16.9-
25.2°C).
On each sampling date, packages of tomato (lkg each) were randomly taken in
triplicate from each treatment for quality analyses. A new package was taken each time
in order to maintain the microenvironment and avoid contamination through repeated
opening and sealing.
4.2.4. Gas sampling and analysis
The analysis of headspace gas concentrations (02, CO2 and N2) during storage was
conducted as described in Chapter 3, section 3.2.4.
4.2.5. Physiological weight Loss (PWL)
PWL was conducted as described in chapter 3, section 3.2.5.
115
Chapter4. Tomato Storage (13CC)
4.2.6. Chemical and biochemical analysis
4.2.6.1. pH and titratabie acidity (TT A)
An extract of an aliquot of juice was prepared according to Nunes and Emond
(1999). An aliquot of tomato juice was extracted from three tomatoes with aKenwood
JE 550 juice extractor. The fruit slurry was filtered through cheesecloth and 100 ml was
centrifuged for 15 minutes at 5000 x g at 4°C. The decanted clear juice was used for the
analysis. The pH value of tomato juice was measured with a Metrohm 691 pH meter.
The TTA of tomatoes were measured by the methods as described by Maul et al.
(2000). The titratable acidity expressed as % citric acid, was obtained by titrating 10 ml
of tomato juice to pH 8.2 with O.lN NaOH with an automatic titrator (665 Dosimat,
Metrohm).
4.2.6.2. Total soluble solids (TSS)
The TSS, expressed as °Brix, during storage was measured as described in chapter 3,
section 3.2.6.1.
4.2.6.3. Free sugar (sucrose, glucose, fructose, sucrose equivalent, SH)
The content of soluble sugars (sucrose, glucose and fructose) of tomatoes was
analysed as described in chapter 3, section 3.2.6.2. For sweetness calculation of the
hexoses, glucose and fructose, their concentrations were converted mathematically to
sucrose equivalents (Koehler and Kays, 1991; Maul et al., 2000). The glucose and
fructose concentrations were multiplied by correction factors 0.74 and 1.73,
respectively, and the sum was considered as sucrose equivalent. The sucrose-hexose
ratios were calculated by dividing sucrose content into the total sum of fructose and
glucose. The sugar-acid ratios were obtained by dividing total sugars by titratabie
acidity.
116
Chapter 4. Tomato Storage (13 'C)
4.2.6.4. Ascorbic acid analysis
The tomato samples were frozen at -20°C on each sampling interval until analysis
was possible within 6 weeks (Maul et al. 2000). The ascorbic acid content of tomatoes
was estimated according to the procedures as described in chapter 3, section 3.2.6.4.
4.2.6.5. Peroxidase activity (POX)
The tomato samples were frozen at -20°C on each sampling interval until analysis
was possible within 6 weeks (El-Zoghbi, 1994, Kato-Noguchi, 1997). The POX in
tomato pericarp tissue (12.5 g) was extracted and the activities were assayed according
to the methods described in chapter 3, section 3.2.5.5.
4.2.6.6. Polygalacturonase activity (PG)
The tomato samples were frozen at -20°C on each sampling interval until analysis
was possible within 6 weeks (El-Zoghbi, 1994, Kato-Noguchi, 1997). Enzyme
extraction was done according to Yoshida et al (1984). Frozen tomato pericarp tissue
(50g) was homogenised for 2 minutes in 100 ml chilled distilled water in a blender.
After the homogenate was centrifuged at 10,000 X g for 15 min, the supernatant was
discarded. The remaining pellet was re-suspended in 25 ml of 0.2 M Tris-HCL buffer
(pH 9.0) that contained 5% NaCI and stirred for 2hr at 4°C. The ensuing slurry was
centrifuged at 15,000 X g for 20 min and its supernatant dialyzed against 3 litres of 20
mM sodium acetate buffer (pH 6.0) for 3 hr.
In order to precipitate protein, 80% (NrL.)2S04 was added to the dialysate. Protein
was collected by centrifugation at 15,000 x g for 20 min and dissolved in a small
amount of water. The protein solution was then dialyzed against 3 I of 20 mM acetate
buffer for 3 hr. All procedures used during the extraction processes were performed at
4°C.
The PG activity was measured by the method of Marangoni et al (1995). The total
PG was analysed in a 1 ml reaction mixture containing 0.1 ml of an aliquot of tomato
extract, 0.2 ml of 0.4 M sodium acetate buffer (pH 4.5), 0.2 ml of 0.4 M NaCI and 0.5
117
Chapter 4. Tomato Storage (13 CC)
ml of 0.5% polygalacturonic acid. The mixture was incubated at 37°C for 30 min, and
the reaction terminated by suspending the mixture in a boiling water bath for 5 min.
Blanks were prepared by heating duplicate samples for 5 min at 100°C prior to the
assay. The reducing groups formed during the 30 min of incubation at 37°C were
estimated by the arsenomolybdate method of Nelson (1944). The PG activity was
expressed as nmole reducing groups min-I. g-I fresh weight.
4.2.7. Microbiological analysis
The estimation of the population of total aerobic bacteria, moulds and yeasts, and
total coli forms were accomplished as described in chapter 3, section 3.2.7. Microbial
populations were not analysed immediately after disinfection, as they were assumed to
be around 0 loglOeUF. il as was shown by Seyoum et al. (2003).
4.2.8. Subjective quality analysis
The marketable quality was subjectively assessed according to Mohammed et al.
(1999). On each sampling time a package of tomatoes containing 5 fruits was randomly
selected from each treatment group. The number of marketable fruits was used as
measure to calculate the percentage marketable fruits during storage. A 1 - 9 rating with
1 = unusable, 3 = unsaleable 5 = fair, 7 = good and 9 = excellent was used to evaluate
the fruit quality. The color, shininess, surface defects, sign of mould growth and
dehydration were visual parameters for the rating. Tomatoes that received a rating of 5
or above were considered marketable, while those rated less than 5 were considered
unmarketable.
4.2.9. Experimental design and data analysis
The experimental design and data analyses were according to the methods as
described in chapter 3, section 3.2.8.
118
Chapter 4. Tomato Storage (13 'C)
4.3. Results
4.3.1. Headspace gas concentration
The changes in O2 concentration in tomato packages sealed with the Xtend® film are
shown in Figure 4.1. The storage temperature highly (P S 0.001) affected 02 levels in
the headspace of packages of tomatoes during storage. The results presented in Figure
4.1 show that ambient temperature storage increased O2 utilisation as a result of higher
respiration rates of fruit. A rapid decrease in 02 concentration in packages of tomatoes
stored at room temperature to below 18.6% was evident after the first five days of
storage, followed by an equilibration of the O2 concentration. During the first five days
of storage the O2 concentration in packages of tomatoes stored at 13°C remained above
19%, after which it dropped up to 12 days, slightly increased up to 20 days and then
stabilised at approximately 19% thereafter.
The disinfecting treatment also had a significant (P S 0.05) effect on the changes in
02 concentrations in packages. After 12 days at 13°C, the O2 concentration decreased to
18.5% in packages of ComCat® treated as well as control tomatoes dipped in
chlorinated water, while that of the anolyte treated tomatoes remained above 19%. After
19 days at 13°C the O2 concentrations of the chlorine disinfected tomatoes equilibrated
at approximately 19%.
There was a difference in the O2 concentrations in packages of ComCat® treated
tomatoes dipped in anolyte after five days at room temperature, being above 19%, while
all other tomato packages stored at room temperature had O2 concentrations below
18.5%. In general, the O2 concentration in packages of ComCat® treated tomatoes
dipped in anolyte water was found to follow O2 content pattern of tomatoes stored at
13°C.
The two-way interaction between preharvest treatment and storage temperature was
highly significant (P S 0.001) on the changes of O2 levels in tomato packages. The
three-way interaction between preharvest, disinfecting and storage temperature factors
119
Chapter 4. Tomato Storage (13 'C)
21.5
-+--ComCat, Chlorinated, MAP, J3°C -----ComCat, Anolyte, MAP, J3°C
21 ... 0· .. ComCat, Anolyte, MAP, RT ----1~ComCat, Chlorinated, MAP, RT---'-ComCat, Water, MAP, J3°C _. *.-ComCat, Water, MAP, RT
~Control, Chlorinated, MAP, 13°C lK Control, Anolyte, MAP, J3°C
20.5 ••• 1;) ••• Control, Anolyte, MAP, RT o Control, Chlorinated, MAP, RT
---Control, Water, MAP, 13°C 1:. Control, Water, MAP, RT
,--.,
::!(
0
'-" 20 .
.:::caQ
Ë 19.5 _
Q)
~
0 19 _
CJ
s::
~
?2 18.5 _ ti
0 ..- .. - .. -, ..-....::()
18 _
... .'
17.5 _ " . .g'
17 _[_
0 5 10 15 20 25 30 35
Storage titre (days)
Figure 4.1. Changes in O2 content (%) in packages oftomatoes in Xtendil!;film stored at
13°C and room temperature (RT) for 30 days (n = 3 over five storage times).
Significance level showing the effect of pre- and postharvest treatment on O2
concentrations
Significance
Preharvest treatment (A) **
Disinfecting (B) **
Storage temperature (C) ***
AXB NS
AXC ***
BXC NS
AXBXC ***
NS, *, **, *** Nonsignificant or significant at P ~ 0.01, 0.05 or 0.00 I respectively. LSDo.05 Value =
0.563, S.E. = 0.034 and C.V. = 0.018.
120
Chapter 4. Tomato Storage (13 'C)
9 -,----------------------------------------------
• ComCat, Chlorinated. MAP, BOC • ComCat, Anolyte, MAP, l3°C
8 .. ·0···ComCat, Anolyte, MAP, RT -I-- ComCat, Chlorinated, MAP, RT
• ComCat, Water, MAP, l3°C _.*.- ComCat, Water, MAP, RT
~ Control, Chlorinated, MAP, l3°C )I( Control, Anolyte, MAP, BOC
••• !;J ••• Control, Anolyte, MAP, RT ... 0- .. Control, Chlorinated, MAP, RT
---4__ Control, Water, MAP, l3°C .. ·b··· Control, Water, MAP, RT
5 - .. ' '~"
9.. ~- ...... ..A._ .. - .. ,
4 - ~~"-~~::... :..':: <. -4.> .lI:h • 0
o ._-------------------------------------------------
o 5 10 15 20 25 30 35
Days after packaging
Figure 4.2. Changes in CO2 content (%) in packages of tomatoes in Xtend® film stored
at 13°C and room temperature (RT) for 30 days (n = 3 over five storage time).
Significance level showing the effect of pre- and postharvest treatment on CO2
concentrations
Significance
Preharvest treatment (A) NS
Disinfecting +MAP (B) *
Storage temperature (C) ***
AXB NS
AXC NS
BXC NS
AXBXC ***
NS, *, *** Nonsignificant or significant at P :$; 0.05 or 0.001 respectively. LSDo.o5 Value = 1.303, S.E. =
0.064 and e.V. = 0.278.
121
Chapter 4. Tomato Storage (13 CC)
were also found to be highly significant (P ::;0.001) on the changes in O2 level in tomato
packages during 30 days of storage at 13°C and 19 days of storage at room temperature.
The storage temperature was the dominant factor affecting C02 concentrations in the
headspace of tomato packages during storage, and was highly significant (P ::; 0.001).
The C02 concentrations in packages of tomatoes subjected to pre- and postharvest
treatments showed differences at room temperature, compared to those stored at 13°C.
The C02 level increased slowly up to 12 days of storage to between 2.0% and 3.5% and
seemed to equilibrate thereafter in packages stored at 13°C (Figure 4.2). In tomato
packages stored at room temperature, CO2 levels of 3.5 to 4.5% were reached after 12
days, after which these levels dropped to between 2.0% and 3.5%.
A C02 level of 4% was reached quickly, after 3 days, in packages of control fruits,
compared to the ComCat® treated tomatoes, and stayed higher up to 12 days of storage.
After 12 days of storage the CO2 level continued to increase in packages of ComCat®
treated fruits except in the case of anolyte water treated tomatoes stored at room
temperature. These differences, however, were not significant (P > 0.05).
The C02 concentration was significantly (P ::; 0.05) affected by the prepackaging
disinfecting treatments. The C02 concentrations increased in all packages of ComCat®
treated tomatoes stored at 13°C, and which were subjected to different disinfectant and
water treatments, up to day 12, declined and stabilised thereafter. At room temperature
storage, the chlorine washed ComCat® treated tomatoes showed a C02 level of 4% after
3 days, which was in the same order of magnitude as for the controls. The C02 level
dropped between days 5 and 12, but then increased sharply at 19 days to above 5.5%. At
19 days storage the CO2 levels of packages of water washed ComCat® treated tomatoes
also increased sharply, but to 4%. The CO2 levels of anolyte washed ComCat® treated
tomatoes stored at room temperature, on the contrary, were much lower and followed
the CO2pattern oftomatoes stored at 13°C.
122
Chapter 4. Tomato Storage (13 'C)
83
82.5 .• C,
.!~'"I . .
,.-... 82
~ .••.. '-,: -<>0
'--'
c 81.5 '1>1
..$2r..o..
lc:l 81 -
(lJ
u
C
u0 80.5
c
&
.0 80ze --+--ComCat, Chlorinated, MAP, )3°C -----ComCat, Anolyte, MAP, )3°C
79.5 ... 0.·· ComCat, Anolyte, MAP, RT ComCat, Chlorinated, MAP, RT---..-ComCat, Water, MAP, I3°C _. *. -ComCat, Water, MAP, RT
~Control, Chlorinated, MAP, )3°C lK Control, Anolyte, MAP, I3°C
79 ••• 1:] ••• Control, Anolyte, MAP, RT " -o... Control, Chlorinated, MAP, RT
-----Control, Water, MAP, 13°C .. ·A··· Control, Water, MAP, RT
78.5
0 5 10 15 20 25 30 35
Storage tirre (days)
Figure 4.3. Changes in N2 content (%) in packages of tomatoes in Xtend® film stored at
l3°C and ambient temperature (RT) for 30 days (n = 3 over five storage time).
Significance level showing the effect of pre- and postharvest treatment on N2
concentrations
Significance
Preharvest treatment (A) **
Disinfecting (B) **
Storage temperature (C) ***
AXB NS
AXC ***
BXC NS
AXBXC ***
NS, *, *** Nonsignificant or significant at P::; 0.05 or 0.001 respectively. LSDo.05 Yalue = 0.618, S.E. =
0.0175 and C.Y. = 0.005.
123
Chapter4. Tomato Storage (13'C)
There was a highly significant (P ~ 0.001) interaction between preharvest ComCat®
treatment, disinfecting treatments and storage temperature on the response of the N2
contents in packages of tomatoes during the 30 days of storage. The N2 concentrations
increased up to 5 and 12 days storage in packages of tomatoes stored at room
temperature and 13°C respectively. This increase in N2 was followed by an equilibration
between 80.5% and 81% during the rest of the storage period at 13°C. The storage
temperature had a highly significant (P ~ 0.001) effect on the N2 concentration in
packages of tomatoes during storage. The N2 concentrations remained higher in the
packages of tomatoes stored at room temperature i.e. above 81.3%, especially during the
first five days of storage. At day 5 of storage at room temperature, the N2 levels of
control tomatoes, which were disinfected with chlorine or anolyte, increased to above
82%, and stayed higher than the water washed ones throughout storage. The N2 levels
of the ComCat® treated and chlorine washed packaged tomatoes increased to above
81.5% from day 5 to day 12, but dropped to 81% at day 19. The water washed ComCat®
treated tomato packages also had approximately 81.5% of N2 content at day 5, but
dropped to 81% at day 12, while the anolyte treated ones stayed below 81%, following
approximately the same pattern as the tomatoes stored at l3°C.
The two-way interaction between the preharvest ComCat® treatment and storage
temperature had a significant (P ~ 0.001) effect on the changes in the N2 concentration
in packages of tomatoes during storage. The N2 concentrations were also significantly
(P ~ 0.001) influenced by the three-way interaction between preharvest ComCat®
treatment, disinfecting treatments and storage temperature.
4.3.2. Physiological weight Loss (PWL)
MAP plays an important role in reducing loss of moisture from tomatoes during
storage (Table 4.1). MAP had a significant (P < 0.05) effect on reducing the PWL
during storage at both l3°C as well as room temperature. During 24 days of storage, the
PWL was found to be 6.3% and 6.6% more in unpackaged preharvest ComCat® treated
tomatoes and controls respectively, than in packaged fruit stored at room temperature.
124
Chapter 4. Tomato Storage (13 'C)
Table 4.1. Changes in physiological weight loss (%) of tomatoes packaged in
Xtend® film or unpackaged and stored at 13°C and room temperature (RT) for 30
days (n = 3 over four storage times).
Treatment Physiological loss in weight (%)
Day 8 Day 16 Day24 Day 30
1.232efg 2.496 fgh 5.017ghComCat®, ei; MAP, 13°C 5.546 b
ComCat®, Anolyte, MAP, 13°C 0.749g 2.461 fghi 3.728 ghi 4.428 bed
ComCat®, C12, MAP, RT 5.467 ab 5.768 ed 11.597 bed
ComCat®, Anolyte, MAP, RT 4.303 abe 6.118 e 11.415 bed
ComCat®, H20,MAP, 13°C 0.799 g 1.713 ghi 2.813 ijk
Comf'at", H20, MAP, RT 3.938 abed 4.781 edef 10.390 edef
ComCat®, H20, 13°C 2.930 bedef 4.524 edefg 5.925 def 8.261 a
ComCat®, H20, RT 9.819a 13.452 a 16.712 a
Control, Ch, MAP, 13°C 0.905 fg 2.150 fghi 2.938 ijk 4.132 ede
jk
Control, Anolyte, MAP, 13°C 0.256 g 1.752 ghi 2.239 4.057 ede
Control, ct; MAP, RT 3.953 abed 5.287 ede 12.754 be
Control, Anolyte, MAP , RT 3.538 bede 4.990de 10.743 de
Control, H 0, MAP, 13°C 0.255 g 1.544 ghi 4.435 gh 4.826 be2
Control, H20, MAP, RT 3.291 bedef 5.074 ede 9.240 def
g
Control, H20, l3°C 2.261 defgh 4.522 edefg 5.920 8.252 a
Control, H20, RT 8.688 a 12.488ab 15.863 a
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC NS
BXC ***
AXBXC NS
NS. *, *** Nonsignificant or significant at P ::; 0.05 or 0.001 respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test
(P < 0.05). LSD Value = 2.004, S. E. = 0.079, MSE = 1.535 and e.V. = 0.195.
125
Chapter 4. Tomato Storage (13CC)
At 13°C, the PWL was 3.2% and 3.4% more in unpackaged ComCat® treated and
control tomatoes respectively for 30 days, compared to packaged ones. Packaging in
microperforated Xtend® film not only offered normal respiration of the fruit, but also
significantly (P < 0.05) reduced PWL.
The PWL was highly affected (P ~ 0.001) by the storage temperature during 30 days
of storage at 13°C and 24 days at room temperature. There was a direct correlation
between storage temperature and PWL. The PWL was significantly reduced with MAP
and lower storage temperature. For example, storage of ComCat® treated tomatoes in
MAP for 24 days at 13°C reduced PWL from 11.597 to 5.017, which is a by 56.7%
reduction, compared to tomatoes stored at RT which reduced PWL from 11.415 to
3.728, which is a 67.3% reduction. Similarly, at 13°C, PWL was reduced by 52.0% to
79.2% in controls compared to storage at room temperature. During 24 days of storage,
due to the coupled effect of packaging and storage temperature, PWL was reduced by
83% and 72% in ComCat® treated and untreated tomatoes respectively. In general,
MAP and proper low temperature storage are critical factors for increasing shelf life of
tomatoes without excessive loss of moisture.
The PWL was affected by the prepackaging disinfecting + MAP treatments (Table
4.1). However, the multiple comparison of the treatment mean showed that the
disinfecting treatment had no significant effect on the PWL, suggesting the importance
of MAP in order to reduce moisture loss.
Losses were slightly higher in packages of fruits dipped in chlorine supplemented
water compared to those dipped in anolyte water and stored at 13°C, however, not
significantly. The differences in PWL of tomatoes dipped in chlorinated and anolyte
water observed after 24 days storage at room temperature was significantly (P ~ 0.001)
affected by the interaction between disinfecting treatment, MAP and storage
temperature. During the first 24 days of storage, the PWL was less in water washed
ComCat® treated and control fruits compared to those dipped in chlorine supplemented,
or anolyte water, stored at 13°C. However, the PWL became faster in water washed
126
Chapter 4. Tomato Storage (13 'C)
. ®
fruits stored at 13°C after 24 days of storage. The preharvest ComCat treatment had a
significant (P S 0.05) effect on the PWL of tomatoes during 30 days of storage (Table
4.1). The PWL remained below 6% during 30 days of storage for both ComCat® treated
as well as control tomatoes packaged and stored at 13°C. There was no interaction
between the preharvest and postharvest treatments on the changes in PWL of the fruit,
but the interaction between disinfecting treatment, MAP and storage temperature was
significant (P S 0.001).
4.3.3. Chemical and biochemical changes
4.3.3.1. pH and Total Titratabie Acidity (TT A)
Table 4.2 shows the changes in pH of tomatoes during storage at 13°C and room
temperature. The changes in pH varied between 3.9 and 4.4. The data show that the pH
values of tomatoes generally increased with the ripening process. The packaged control
tomatoes stored at 13°C displayed a decrease in pH during the first 8 days of storage,
followed by an increase. After the fruit became red and overripe, the pH values seemed
to drop, increasing the fruit acidity.
A highly significant (P S 0.001) difference in pH values of groups oftomatoes stored
under different storage temperature was obtained during the storage period as shown in
Table 4.2. Throughout the 30 days storage, the pH of stored fruit was distinctively
higher in both packaged, as well as unpackaged, tomatoes stored at room temperature,
compared to storage at 13°C. The pH also increased faster during storage at room
temperature, indicating a faster ripening process. These data also showed that the
combination of postharvest treatments had a significant effect on the pH value of
tomatoes during storage at 13°C and room temperature. In general, storage at room
temperature resulted in an increase in pH in both chlorine and anolyte treated tomatoes.
The pH values of ComCat® treated fruits dipped in chlorinated water were
significantly (P S 0.001) higher than the values in fruit subjected to anolyte water
dipping treatment during the first 16 days of storage at 13°C, while after 16 days, the
127
Chapter 4. Tomato Storage (13 'C)
Table 4.2. Changes in pH value of tomatoes packaged in Xtend® film or unpackaged
and stored at BOC and room temperature (RT) for 30 days (n = 3 over four storage
times).
Treatment pH
DayO Day8 Day 16 Day24 Day 30
ConrCat'", C12,MAP, BOC 4.062 b 4.150 bede 4.177 de 4.183ef 4.107 de
Comf.at'", Anolyte, MAP, 13°C 4.062 b 4.103ef 4.1 07 fgh 4.190 ef 4.143 be
Comf.at", C12,MAP, RT 4.062 b 4.107 ef 4.213 be 4.350a
Comt.at", Anolyte, MAP, RT 4.062 b 4.083 f 4.187de 4.220 de
Comï.at", H20, MAP, 13°C 4.062 b 4.093 ef 4.133 efgh 4.123 gh 4.130 be
CorrrCat", H20, MAP, RT 4.062 b 4.227a 4.210bed 4.353 a
CorrrCat'", H20, BOC 4.062 b 3.977 g 4.153defg 4.147 efg 4.130 be
Comï.at", H20, RT 4.062 b 4.097 ef 4.280 a 4.267 bed
Control, Ch, MAP, 13-c 4.120a 4.090 ef 4.097 ed 4.117 ghi 4.170ab
Control, Anolyte, MAP, 13-c 4.120 a 4.073 f 4.120 fgh 4.170 ef 4.183 a
Control, Ch, MAP, RT 4.120 a 4.207 ab 4.227 ab 4.293 ab
Control, Anolyte, MAP, RT 4.120 a 4.187 be 4.197 cd 4.310 ab
Control, H20, MAP, 13°C 4.120a 4.190 be 4.157 def 4.083 i 4.170 ab
Control, H20, MAP, RT 4.120 a 4.167bed 4.213 be 4.343 a
Control, H20, 13-c 4.120a 4.000 g 4.163 ef 4.110 hi 4.070 de
Control, H20, RT 4.120 a 4.027 fg 4.203 ed 4.303 ab
Significance
Preharvest Treatment (A) ***
Disinfecting + MAP (B) ***
Storage Temperature (C) ***
AXB ***
AXC ***
BXC ***
AXBXC ***
*** Significant at P ::s: 0.001 respectively. Means within a column followed by the same letter(s) are
not significantly different according to Duncan's multiple range test (P < 0.05). The LSD Value =
0.041, S.E. = 0.002, MSE = 0.001 and C.V. = 0.012
128
Chapter 4. Tomato Storage (13 'C)
pH of anolyte disinfected tomatoes was higher. At room temperature, the pH value
remained higher in control fruit dipped in chlorinated water during the first 8 days of
storage.
At harvest, the pH value of ComCat® treated tomatoes was significantly (P :s 0.05)
lower than in controls. During storage at 13°C the pH in disinfected control tomatoes
dropped after 8 days of storage, and then increased up to 30 days. However, under the
same circumstances, the pH changes in ComCat® treated tomatoes followed a different
pattern, i.e. an increase up to day 24, followed by a decrease up to day 30. At day 30 the
pH was significantly lower than that of the control tomatoes.
The two-way interaction between disinfecting + MAP treatment and storage
temperature was highly significant (P :s 0.001) on the changes in pH of fruits during
storage, suggesting the importance of combining proper postharvest treatments to
improve the shelf life of tomatoes. Similarly, the three-way interaction between pre-and
postharvest treatments, i.e. preharvest ComCat® treatment, disinfecting + MAP and
storage temperature, was highly significant (P :s 0.001) on the changes in the pH values
of the fruit during 30 days of storage.
Table 4.3 displays the changes in TTA of green mature tomatoes during ripening and
storage at 13°C and room temperature, which varied between 0.22% and 0.49%. The
TTA of tomatoes decreased during ripening in storage, both at 13°C as well as room
temperature. Storage temperature had a highly significant (P :s 0.001) effect on the
changes in TTA, when storage at 13°C is compared with storage at room temperature.
Table 4.3 shows that the higher storage temperature resulted in a faster decline in TTA
of tomatoes. After 24 days of storage, the TTA was lower in tomatoes stored at room
temperature compared to storage at 13°C.
Packaging affected the change in TTA significantly. The TTA of tomatoes was lower
during the first 8 days of storage in packaged tomatoes compared to the unpackaged
ones. During the first 24 days storage at room temperature, packaged control tomatoes
129
Chapter 4. Tomato Storage (13 CC)
Table 4.3. Changes in titratable acidity of tomatoes packaged in Xtend® film or
unpackaged and stored at BOC and room temperature (RT) for 30 days (n = 3 over
four storage times).
Treatment TTA (% acetic acid)
DayO Day8 Day 16 Day24 Day 30
ComCat®, Ch, MAP, 13°C 0.472 a 0.365 ede 0.416 ab 0.336 bed 0.368 abc
ComCat®, Anolyte, MAP, 13°C 0.472 a 0.385 def 0.411 abe 0.328 bed 0.336 bed
ComCat®, Ch, MAP, RT 0.472 a 0.402 de 0.331 de 0.261 ef
Comf'at'", Anolyte, MAP, RT 0.472 a 0.393 de 0.337 de 0.326 bed
ComCat®, H20, MAP, 13°C 0.472 a 0.363 def 0.417 ab 0.390 ab 0.288 cd
ComCat®, H20,MAP, RT 0.472 a 0.325 ef 0.317 def 0.225 f
Comf'at", H 0, BOC 0.472 a 0.509a 0.399 be 0.358 abe 0.351 bed2
Comf'at'", H20, RT 0.472 a 0.409 de 0.318 ef 0.333 bed
Control, ei,MAP, BOC 0.387 b 0.473 abe 0.429 ab 0.394 a 0.386 ab
Control, Anolyte, MAP, 13°C 0.387 b 0.435 bed 0.442 a 0.339 abe 0.381 abc
Control, Ch, MAP, RT 0.387 b 0.342 def 0.374 ede 0.291 de
Control, Anolyte, MAP, RT 0.387 b 0.396 de 0.374 bede 0.283 de
Control, H20, MAP, 13°C 0.387 b 0.418 ed 0.392 bed 0.387 ab 0.337 bed
Control, H 0, MAP, RT 0.387 b 0.356 def 0.348 ede 0.282 de2
Control, H20, l3°C 0.387 b 0.487 ab 0.375 bede 0.375 abe 0.402 a
Control, H20, RT 0.387 b 0.468 bed 0.387 bed 0.320 ede
Significance
Preharvest Treatment (A) NS
Disinfecting +MAP (B) ***
Storage Temperature (C) ***
AXB ***
AXC ***
BXC ***
AXBXC ***
NS, *, **, *** Nonsignificant or significant at P ::;0.05, 0.01 or 0.001 respectively. Means within a
column followed by the same letter(s) are not significantly different according to Duncan's
multiple range test (P < 0.05). LSD Value = 0.051, S.E. = 0.017, MSE = 0.0018 and C.V. = 0.019.
130
Chapter 4. Tomato Storage (13 'C)
maintained a lower TTA, compared to unpackaged controls. In general, the disinfecting
treatment did not affect the changes in TTA, except that a significantly higher TTA was
noted for chlorine washed ComCat® treated tomatoes after 24 days of storage at room
temperature.
At harvest, the TTA of ComCat® treated, mature green tomatoes was higher and
significantly different from the TTA of control tomatoes (Table 4.3). However, the
statistical analysis on the overall data during the 30 days of storage showed no
significant differences between the ComCat® treated and controls.
The two-way interaction between preharvest treatment and disinfecting + MAP was
highly significant (P :::;0.001) on the changes in TTA of tomatoes. Similarly, there was a
significant (P :::;0.001) interaction between preharvest ComCat® treatment and storage
temperature on the changes in TTA content of fruit during the 30 days of storage. There
was also a significant (P :::;0.001) interaction between disinfecting + MAP and storage
temperature on the response to TTA content of tomatoes, and the three way interaction
between pre- and postahrvest treatments was also highly significant (P:::;0.001).
4.3.3.2. Total soluble solids (TSS)
The TSS of tomatoes varied between 4.0 and 5.0 °Brix in this study (Table 4.4). In
general, the TSS of tomatoes increased during the first 8 days of storage and dropped
thereafter. MAP had a significant (P ~ 0.05) effect on the TSS of tomatoes during
ripening in storage. At room temperature, unpackaged control tomatoes displayed a
higher TSS from 8 to 16 days of storage than packaged ones. At 13°C storage,
unpackaged tomatoes showed the lowest TSS's for ComCat® treated tomatoes from day
16 to day 30. In the control tomatoes the TSS of unpackaged tomatoes was distinctly
different from all the packaged ones at any time interval, however, a specific pattern
was not visible.
Storage temperature was one of the main factors governing the changes in TSS
content of tomatoes. Tomatoes that were disinfected before packaging, showed a
131
Chapter 4. Tomato Storage (13 CC)
Table 4.4. Changes in total soluble solid (TSS) of tomatoes packaged in Xtend® film
or unpackaged and stored at l3°C and room temperature (RT) for 30 days (n = 3 over
four storage times).
Treatment Total soluble solid TSS (OBrix)
DayO Day8 Day 16 Day24 Day 30
ComCat®, Ch, MAP, l3°C 4.360a 4.767 be 4.500 bedef 4.403 e 4.267 bed
4.360a 4.502 efg 4.697aComCat®, Anolyte, MAP, l3°C 4.797 a 4.337 ab
ComCat®, Ch, MAP, RT 4.360a 4.760 be 4.487 edef 4.344 d
b
ComCat®, Anolyte, MAP, RT 4.360a 4.393 hi 4.523 bede 4.597
ComCat®, H20, MAP, l3°C 4.360a 4.627 d 4.613 abe 4.240 def 3.997 f
ComCat®, H20, MAP, RT 4.360a 4.327 ij 4.593 be 4.003 h
ComCat®, H 0, l3°C 4.360a2 4.593 def 4.033 i 4.033 h 4.050 ef
ComCat®, H20, RT 4.360a 4.917 a 4.537 bede 4.410 e
Control, ei; MAP, 13°C 4.248 ab 4.750 be 4.190
jk 4.390 ed 4.393 ab
Control, Anolyte, MAP, 13°C 4.248 ab 4.417hi 4.410gh 4.421 be 4.400 r
Control, Ch, MAP, RT 4.248 ab 4.433 ghi 4.423 gh 4.333 de
Control, Anolyte, MAP, RT 4.248 ab 4.817 ab 4.493 bedef 4.200 fg
jk
Control, H20, MAP, l3°C 4.248 ab 4.583 def 4.190 4.197 g 4.033 f
Control, H20, MAP, RT 4.248 ab 4.483 fgh 4.593 bed 4.397 e
Control, H20, l3°C 4.248 ab 4.433 ghi 4.493 edef 4.197 g 4.147
de
Control, H20, RT 4.248 ab 4.833 ab 4.677 a 4.033 h
Significance
Preharvest Treatment (A) **
Disinfecting +MAP (B) **
Storage Temperature (C) ***
AXB *
AXC ***
BXC ***
AXBXC **
**, *** Significant at P ~ 0.0 I or 0.00 I respectively. Means within a column followed by the same
letter(s) are not significantly different according to Duncan's multiple range test (p<0.05). The LSD
Value = 0.072, S.E. = 0.003, MSE = 0.002 and C.V. = 0.0 II.
132
Chapter 4. Tomato Storage (13'C)
significantly different profile ofTSS changes during storage at 13°C, with water washed
tomatoes having the lowest TSS content from day 24 on. There was also a difference
between the disinfecting treatments, in that the anolyte dipped tomatoes contained more
TSS than the chlorine dipped ones, from day 16 onwards.
At room temperature storage the ComCat® treated tomatoes had higher TSS contents
after disinfecting. The highest TSS content, from day 16 onwards, was observed for
ComCat® treated tomatoes disinfected with anolyte. Water washed control samples had
the lowest TSS content at day 8 of storage, but they reached higher contents from day
16 on, compared to the disinfected ones. Disinfecting + MAP in general resulted in
significantly (P :::;0.01) different TSS changes during storage. Storage temperature also
had a significant (P :::;0.001) influence on the TSS content. The TSS content of
unpackaged tomatoes was higher when stored at room temperature in ComCat® treated
tomatoes throughout storage. In unpackaged control tomatoes, the TSS content was
significantly (P < 0.05) higher during room temperature storage up to day 16. Other
comparisons did not result in a specific pattern regarding storage temperature.
ComCat® treatment resulted in a higher TSS content at harvest, however, not
significantly (P > 0.05) higher. During storage, significant differences were observed (P
:::;0.001). ComCat® treated tomatoes had higher trends of TSS contents during storage
after disinfection than the control, while the TSS contents were observed to be lower
when not disinfected. These results suggested that coupled effects exist, which was
confirmed by the statistical analysis. Significant two-way interactions (P > 0.001) and a
three-way interaction (P > 0.01), were obtained between all the treatments.
4.3.3.3. Free sugar
The free sugars consist of glucose and fructose, present in approximately equal
amounts. In this study, the sucrose content remained below 0.1 g. 100 g" during the 30
days of storage, both at l3°C and room temperature (Table 4.5). The sucrose content
increased during the first 8 days of storage, but declined thereafter during storage at
both temperatures.
133
Chapter4. Tomato Storage (13CC)
Disinfecting treatments and packaging showed no significant effect on the sucrose
content at both storage temperatures.
Storage temperature had a significant (P ~ 0.001) effect on the sucrose content. At
13°C the sucrose content increased up to 8 days, from 0.03 g.100g-1 to above 0.04
g.1OOg-I,followed by a slow return thereafter, to around the initial values after 24 days.
At room temperature, a decrease to below the initial values is observed in most of the
tomato samples subjected to different treatments after day 16 of storage.
The preharvest ComCat® treatment had a significant (P ~ 0.05) effect on the changes
in sucrose content of tomatoes. In general, the sucrose content was found to be slightly
lower in ComCat® treated fruits during the 30 days of storage. The effect was mainly
expressed in tomatoes stored at room temperature, where the sucrose content of the
ComCat® treated tomatoes was observed to drop to lower levels, i.e. below 0.027
g.1OOg-I,from day 16 onwards, as compared to the controls.
The sucrose content of tomatoes was not significantly affected by the interaction of
preharvest ComCat® treatment and prepackaging disinfectant +MAP. However, sucrose
content was influenced by the interaction of preharvest ComCat® treatment and storage
temperature. These results confirm that, in order to maintain the sucrose content of
ComCat® treated tomatoes, the proper storage temperature should be maintained during
storage. The interaction between different postharvest treatments (disinfecting, MAP
and storage temperature) had a slight influence on the changes in sucrose content of
tomatoes stored at 13°C as well as at room temperature.
The range of the values of glucose (between 0.077 g.100 g-I and 1.24 g.100 g-I) and
fructose (between 1.01 g.100 g-I and 1.58 g.100 g-I) in tomatoes found in this study was
similar to those reported by Maul et al. (2000). MAP slightly reduced the rate of
glucose utilisation during storage (Table 4.5 (b)). Throughout storage the glucose
content was found to be higher in packaged than in unpackaged fruits. Disinfecting
treatment also resulted in different glucose dynamics. In general, the glucose levels
were lower after 16 days of storage at 13°C in water washed tomatoes, compared to the
134
Chapter4. Tomato Storage (13CC)
Table 4.5 (a). Changes in sucrose content of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3 over
four storage times).
Treatment Sucrose (g. I OOg-1)
day 0 da~ 8 Day 16 day24 day 30
CorrrCat'", Ch, MAP, 13°C 0.030a 0.042 abed 0.033 abed 0.030 abe 0.032 a
ComCat®, Anolyte, MAP, 13°C 0.030a 0.044 abe 0.028 bede 0.025 bede 0.029ab
de
ComCat®, Ch, MAP, RT 0.030a 0.039bedefg 0.027 edef 0.020
ComCat®, Anolyte, MAP, RT 0.030a 0.038bedefg 0.028 edef 0.022 de
Cornf'at'", H20, MAP, 13°C 0.030a 0.050 a 0.026 edef 0.024 ede 0.028 abe
ComCat®, H20, MAP, RT 0.030a 0.043 abc 0.026 edef 0.020 de
a a
Cornf'at'", H20, 13°C 0.030a 0.040 bedef 0.039 0.033 ab 0.030
ComCat'", H20, RT 0.030a 0.036 edefg 0.024 def 0.019 e
Control, Ch, MAP, 13°C 0.031 a 0.043 abc 0.035 abe 0.033 ab 0.033 a
Control, Anolyte, MAP, 13°C 0.031 a 0.041 bede 0.037 ab 0.034 a 0.028 abe
Control, ei, MAP, RT 0.031 a 0.047 ab 0.034 abc 0.031 abc
Control, Anolyte, MAP, RT 0.031 a 0.040 bedef 0.034 abc 0.028 bed
Control, H20, MAP, 13°C 0.03a 0.042 abed 0.029 bede 0.032 abc 0.032 a
Control, H20, MAP, RT 0.03a 0.041 bed 0.031 abed 0.031 abc
Control, H20, 13°C 0.03a 0.047 ab 0.033 abed 0.033 ab 0.031 a
Control, H20, RT 0.03a 0.041 bed 0.027 edef 0.024 ede
Significance
Preharvest treatment (A) *
Disinfecting + MAP (B) NS
Storage temperature (C) ***
AXB NS
AXC ***
BXC *
AXBXC NS
NS, *, *** Nonsignificant or significant at P ~ 0.05 or 0.001 respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range
test (P < 0.05). The LSD Value = 0.007, S.E. = 0.003, MSE = 0.001 and e.v. = 0.139.
135
Chapter 4. Tomato Storage (13 CC)
chlorine and anolyte washed ones. At room temperature, the glucose content was higher
at days 16 in water washed tomatoes, before dropping to lower values.
Although the difference was not significant (P > 0.05), anolyte dipping resulted in a
higher glucose content after 24 days of storage at 13°C in ComCat® treated tomatoes,
and higher contents at days 8 and 16 at room temperature, compared to the chlorine
dipped tomatoes. ComCat® treatment was shown to have a significant (P ~ 0.05) effect
on the glucose content of tomatoes during storage, and was, in general, lower from
harvest throughout storage. The changes in glucose content were not affected by the
interaction of preharvest treatment and disinfecting + MAP, but was highly influenced
by the interaction of preharvest treatment and storage temperature. Table 4.5 (c) shows
the changes in fructose in tomatoes stored at 13°C as well as room temperature.
Unlike changes in glucose, the fructose content increased during the active period of
the ripening process, until the fruit were close to the climacteric peak. Only from the
full ripe and overripe stages of the fruit, did the fructose content decrease.
In general, the packaged tomatoes showed higher levels of fructose at both storage
temperatures. Disinfection did not have a very obvious effect on the fructose content,
however, lower fructose contents were noted in chlorine and anolyte dipped samples at
8 days of storage at 13°C and 8 and 16 days storage at room temperature, compared to
the water washed ones. The fructose content of ComCat® treated tomatoes was lower at
harvest and generally had a slightly higher fructose content in tomatoes dipped in
chlorinated and anolyte water during storage at 13"C.
The fructose content was not affected by the interaction between ComCat® treatment
and disinfecting + MAP, but was influenced by the interaction between preharvest
ComCat® treatment and storage temperature. The three-way interaction between
preharvest ComCat® and postharvest treatments i.e. disinfecting, MAP and storage
temperature influenced the changes in fructose concentration at p ~ 0.05 significance
level.
136
Chapter 4. Tomato Storage (13 CC)
Table 4.5 (b). Changes in glucose content of tomatoes packaged in Xtend® film or unpackaged
and stored at 13°C and room temperature (RT) for 30 days (n = 3 over four storage times).
Treatment Glucose (g. IOOg-I)
day 0 Day8 day 16 day 24 day 30
ComCat®, Ch, MAP, 13°C 1.374 1.193 abc 1.177 abc 0.994 abc 1.026 abab
ComCat®, Anolyte, MAP, 13°C 1.374 ab 1.017 edef 1.017ed 1.157 a 1.120 a
ComCat®, Ch, MAP, RT 1.374 ab 1.013 edef 0.978 ede 0.952 abed
Comf'at", Anolyte, MAP, RT 1.374 ab 1.023 edef 1.018 ed 0.852 ede
Comf.at", H20, MAP, 13°C 1.374 ab 1.213 ab 1.171 abc 0.967 abed
Comï.at", H20, MAP, RT 1.374 ab 1.138 abc 1.134 bed 0.890 bede
CorrrCat'", edH 0, 13°C 1.374 ab 0.872 efg 1.010 0.972 abed 0.929 abc2
Comï.at'", H20, RT 1.374 ab 0.959 defg 1.042 ede 0.751 e
Control, Ch, MAP, 13°C 1.394 a 1.279 a 1.270 a 1.037 abc 1.077 a
Control, Anolyte, MAP, 13°C 1.394 a 1.268 a 1.243 ab 1.021 abc 1.044 ab
Control, Ch, MAP, RT 1.394 a 1.099 bede 1.203 abc 1.017 abc
Control, Anolyte, MAP, RT 1.394 a 1.220 ab 1.219 ab 1.016 abc
Control, H20, MAP, l3°C 1.394 a 1.176 abc 1.168abed 0.984 abed 1.015 ab
Control, H20, MAP, RT 1.394 a 1.170 abc 1.302 a 1.042 abc
Control, Water, 13°C 1.394 a 1.150 abed 1.118 abed 0.965 abed 0.901 abc
Control, water, RT 1.394 a 1.027 edef 0.897 ef 0.776 abc
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC ***
BXC *
AXBXC NS
NS, *, ** Nonsignificant or significant at P:;; 0.05 or 0.01 respectively. Means within a column followed by the
same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The LSD
Value = 0.169, S. E. = 0.019, MSE = 0.011 and C.V. = 0.095.
137
Chapter 4. Tomato Storage (13 CC)
Table 4.5 (c). Chariges in fructose content of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3 over four
storage times).
Treatment Fructose (g. IOOg-I)
day 0 day 8 day 16 day24 day 30
ComCat®, Ch, MAP, 13°C 1.287 ab 1.359 abede 1.499 ab 1.431 ab 1.290 a
ComCat®, Anolyte, MAP, 13°C 1.287 ab 1.272 bede 1.377 abc 1.535 a 1.348 a
ComCat®, Ch, MAP, RT 1.287 ab 1.161 de 1.226 edef 1.223 bed
ComCat®, Anolyte, MAP, RT 1.287 ab 1.167de 1.269 bede 1.131 ed
ComCat®, H20, MAP, 13°C 1.287 ab 1.527 ab 1.486 abc 1.305 abc 1.326 a
ComCat®, H20, MAP, RT 1.287 ab 1.155 de 1.324 abed 1.181 ed
ComCat®, H20, 13°C 1.287 ab 1.141
e 1.320 abed 1.354 ab 1.221 ab
ComCat®, H20, RT 1.287 ab 1.164 de 1.142 f 1.049 d
Control, Ch, MAP, 13°C 1.371 a 1.556 a 1.387 abed 1.310 abc 1.264 ab
Control, Anolyte, MAP, 13°C 1.371 a 1.393 abede 1.552 a 1.258 bed 1.141 b
Control, ei, MAP, RT 1.371 a 1.322 abede 1.489 1.221 bed
Control, Anolyte, MAP, RT 1.371 a 1.464 ab 1.472 abc 1.304 abc
Control, H20, MAP, 13°C 1.371 a 1.449 abc 1.462 abc 1.328 ab 1.269 ab
Control, H20, MAP, RT 1.371 a 1.593 a 1.577 a 1.266 abc
Control, H20, 13°C 1.371 a 1.418 abede 1.411 abed 1.349 ab 1.212 ab
Control, H20, RT 1.371 a 1.445 abc 1.176 ef 1.013 d
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) *
Storage temperature (C) ***
AXB NS
AXC **
BXC NS
AXBXC *
NS, *, **, *** Nonsignificant or significant at P ~ 0.05, 0.0 I or 0.00 I respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test (P <
0.05). The LSD Value = 0.210, S.E. = 0.016, MSE = 0.017 and C.V. = 0.100.
138
Chapter 4. Tomato Storage (13 "C)
4.3.3.4. Total soluble sugar
Table 4.6 displays the total soluble sugar content calculated from the summation of
sucrose, glucose and fructose content of tomatoes during the storage, which varied
between 1.8 g.100-lg and 2.96 g.100-1• The total soluble sugar decreased faster in
Table 4.6. Changes in total sugar content of tomatoes packaged in Xtend® film or
unpackaged and stored at l3°C and room temperature (RT) for 30 days (n = 3 over four
storage times).
1
Treatment Total soluble sugar (g.100g- FW)
Da~O Day8 Day 16 Da~24 Da~30
ConrCat", Ch, MAP, 13°C 2.691 ab 2.595abed 2.802 ab 2.456 abc 2.348 a
CorrrCat'", Anolyte, MAP, 13°C 2.691 ab 2.536 abede 2.422 bedef 2.717 a 2.497 a
Comf'at'", Ch, MAP, RT 2.691 ab 2.214 defg 2.230 edefg 2.195
bed
Comï.at'", Anolyte, MAP, RT 2.691 ab 2.229 defg 2...,1" edefg.) .) 2.003 cd
ComCat'", H20, MAP, 13°C 2.691 ab 2.791 abc 2.683 abed 2.296 abed 2.384 a
Cornï.at", H20, MAP, RT 2.691 ab 2.368 edef 2.484 bede 2.091 cd
Comf'at'", H20, 13°C 2.691 ab 2.204 defg 2.369 bedef 2.359 abc 2.181 ab
, Cornï.at'", H20, RT 2.691 ab 2.160 efg 2.064 egf 1.819 d
Control, Ch, MAP, 13°C 2.796 a 2.879 ab 2.465 bede 2.380 abc 2.374 a
Control, Anolyte, MAP, 13°C 2.796 a 2.701 abc 2.832 ab 2.314 abed 2.213 ab
Control, ei, MAP, RT 2.796 a 2.469 abede 2.726 abc 2.269 bed
Control, Anolyte, MAP, RT 2.796a 2.754 abc 2.725 abc 2.348 abc
Control, H20, MAP, 13°C 2.796 a 2.667 abed 2.659 abed 2.344 abc 2.317 b
a
Control, H20, MAP, RT 2.796 a 2.954 a 2.910 2.339 abc
Control, H20, 13°C 2.796 a 2.615 abed 2.562 abede 2.347 abc 2.144 ab
Control, H20, RT 2.796 a 2.647 abed 2.159 defg 1.818 d
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) *
Storage temperature (C) ***
AXB NS
AXC ***
BXC NS
AXBXC NS
NS, *, *** Nonsignificant or significant at P ~ 0.05 or 0.001 respectively. Means within a column followed
by the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05).
The LSD Value = 0.042, S.E.= 0.042, MSE = 0.064 and C.V. = 0.103.
139
Chapter 4. Tomato Storage (13CC)
unpackaged tomatoes stored at room temperature, as well as at BOC. No conclusion
could be drawn from the disinfecting treatment in terms of the total soluble sugar
content, when compared with each other, or with the water washed samples.
Storage temperature had a significant (P ~ 0.001) effect on the total soluble sugar of
packaged stored tomatoes. Storage at room temperature generally resulted in lower total
soluble sugar levels than that oftomatoes stored at BOC from day 16 onwards.
ComCat® treatment resulted in tomatoes having a lower total soluble sugar than the
controls at harvest, although not significantly (P > 0.05). This difference was continued
up to 8 days at both temperatures. From day 24 onwards, the ComCat® treated tomatoes
stored at BOC had a higher total soluble sugar than the controls, except for the chlorine
washed samples.
The interaction between ComCat® treatment and storage temperature had an
influence on the changes in total soluble sugar of tomatoes during storage at 13°C and
room temperature. In general, the results showed that the overall sugar content of
tomatoes was maintained better when preharvest ComCat® treatment is combined with a
proper disinfecting treatment, MAP and low storage temperature.
4.3.3.5. Sucrose equivalent
Table 4.7 displays the sucrose equivalent (g. 100-1 g) in tomato fruits subjected to
different pre-and postharvest treatments and stored either at 13°C or room temperature.
The values were calculated from experimentally obtained glucose and fructose values,
as being between 2.32 g.lOO-1and 3.73 g.lOO-I, and is an indication of the sweetening
power of these sugars (Maul ef al., 2000). The general trend of the sucrose equivalent
was to drop to lower values during storage, from above 3.2 g.lOO-1to below 3.0 g.lOO-I,
except for anolyte washed ComCat® treated tomatoes.
Packaging affected the sucrose equivalent such that sucrose equivalent values
dropped to lower values in unpackaged tomatoes. Disinfecting + MAP had a significant
(P ~ 0.05) effect on the sucrose equivalent of tomatoes during storage. Anolyte washed
140
Chapter 4. Tomato Storage (13 'C)
ComCa{~ treated tomatoes had higher sucrose equivalent values from 24 days of storage
on, compared to water washed and chlorine disinfected ones. However, the control
Table 4.7. Changes in sucrose equivalent (g.100-l g fresh weight) of tomatoes packaged
in Xtend® film or unpackaged and stored at 13°C and room temperature (RT) for 30 days
(n == 3 over four storage times).
Treatment Sucrose Equivalent (g.100g-
l FW)
DayO Day8 Day 16 Day24 Day 30
3.244 ab 3.137abede 3.465 abe 2.357 ef 2.990a
ComCat®, Anolyte, MAP, 13°C 3.244 ab 2.954 edef 2.970 edef 3.511 a 3.161 a
ComCat®, C12, MAP, RT 3.244 ab 2.759 def 2.845 defgh 2.820 edef
ComCat®, Anolyte, MAP, RT 3.244 ab 2.776 edef 2.948 edef 2.588 ef
Comf'at", H20, MAP, 13°C 3.244 ab 3.540 ab 3.437 abe
2.974 bede 3.055 a
Cornf'at'", H20, MAP, RT 3.244 ab 3.580 a
3.130 abedef2.702 def
ef
ComCat®, H20, 13°C 3.244 ab 2.618 3.031 bedef 3.062 abed2.800 abe
Cornf'at'", H20, RT 3.244 ab 2.724 def 3.105 abedef2.371 ef
Control, Cb, MAP, 13°C 3.403 a 3.639 a 3.171 abedef3.033 abed2.984 ab
Control, Anolyte, MAP, 13°C 3.403 a 3.274 ab 3.605 ab 2.933 bede2.747 be
Control, Cl-, MAP , RT 3.403 a 3.1 01 abede 3.467 abe 2.864 edef
Control, Anolyte, MAP, RT 3.403 a 3.458 abed 3.448 abe 3.007 abed
Control, H20, MAP, 13°C 3.403 a 3.377 abe 3.393 abed
3.026 abed 2.981 ab
Control, H20, MAP, RT 3.403 a 3.732 a 3.691 a 2.961 bede
Control, H20, 13°C 3.403 a 3.304 abed
3.269 abcde 3.048 abed 2.764 be
Control, H20, RT 3.403 a 3.359 abe 2.743 efgh 2.327 f
Significance
Preharvest treatment (A) *
Disinfecting + MAP (B) *
Storage temperature (C) ***
AXB NS
AXC ***
BXC NS
AXBXC *
NS, *, *** Nonsignificant or significant at P ~ 0.05 or 0.00 I respectively. Means within a column followed
by the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05).
The LSD Value = 0.492, S.E. =0.040, MSE = 0.093 and e.v. = 0.099.
141
Chapter 4. Tomato Storage (13 CC)
tomatoes disinfected with anolyte showed lower sucrose equivalent values during the
same storage period. No conclusive deductions could therefore be made from
comparisons of the disinfecting treatments amongst each other, or with the water
washed tomatoes.
The storage temperature was highly significant (P ~ 0.001) on the sucrose equivalent,
in that the lowest levels were reached after 24 days of storage at room temperature,
compared to 30 days storage at l3°C.
The sucrose equivalent was lower in ComCat® treated tomatoes at harvest, although
not significant, and remained lower in most of the tomato samples throughout storage
when compared to the controls (P ~ 0.05), except for anolyte washed ComCat® treated
tomatoes. It was also not influenced by the interaction between the preharvest treatment
with disinfecting + MAP. The interaction between the preharvest ComCat® treatment
and storage temperature had a significant effect on the sucrose equivalent (P ~ 0.001).
The three-way interaction between the pre-and postharvest treatment also had a
significant (P ~ 0.05) effect on the sucrose equivalent.
4.3.3.6. Sucrose-hexose ratio
The sucrose-hexose (SH) ratio varied between 0.009 and 0.021, and increased during
the first 8 days of storage (Table 4.8), followed by a general decrease from day 16 on.
The SH ratios were slightly affected by storage temperature, with tomatoes stored at
13°C showing higher values.
The SH ratio was slightly influenced with the disinfecting + MAP treatment, but the
difference here was not distinct between the SH ratio values for tomatoes disinfected by
chlorinated or anolyte water, nor water wash, during storage. The SH ratio was slightly
affected by the preharvest ComCat® treatment during storage at 13°C as well as room
temperature. Only during the early stage of storage (day 8) was the sucrose-hexose ratio
significantly higher in preharvest ComCat® treated tomatoes at both storage
142
Chapter 4. Tomato Storage (13 CC)
temperatures. None of the two-way interactions between pre- and postharvest
treatments had an influence on the changes in SH ratio during storage.
Table 4.8. Changes in SH ratio of tomatoes packaged in Xtend® film or unpackaged and stored
at 13°C and room temperature (RT) for 30 days (n = 3 over four storage times).
Treatment Sucrose-hexose ratio
DayO Day8 Day 16 Day24 Day 30
Comf'at", ei; MAP, 13°C 0.011 a 0.017 ede 0.012 ed 0.012 de 0.014 abc
g
ComCat®, Anolyte, MAP, 13°C 0.011 a 0.018be 0.011 de 0.009 0.012 ede
0.011 0.019 ab 0.012 cd 0.009gComCat®, ei;MAP, RT a
Comf'at", Anolyte, MAP, RT 0.011 a 0.018 be 0.012 cd 0.010 fg
ComCat®, H20, MAP, 13°C 0.011 a 0.019 ab 0.010 ef 0.011 ef 0.012 ede
ComCat®, H20, MAP, RT 0.011 a 0.019 ab 0.010 ef 0.010 fg
ComCat®, H20, 13°C 0.011 a 0.019 ab 0.017 a 0.014 be 0.014 abe
Comf'at'", H20, RT 0.011 a 0.017 ede 0.012 cd 0.010
fg
Control, Ch, MAP, 13°C 0.011 a 0.016 ef 0.014 b 0.014 be 0.014 abc
Control, Anolyte, MAP, 13°C 0.011 a 0.016 ef 0.013 be 0.015 ab 0.013 bed
Control, Ch, MAP, RT 0.011 a 0.021 a 0.013 be 0.014 be
be
Control, Anolyte, MAP, RT 0.011 a 0.015 fg 0.013 0.012 de
Control, H20, MAP, 13°C 0.011 a 0.016
ef 0.011 de 0.014 be 0.014 abc
Control, H20, MAP, RT 0.011 a 0.014 gh 0.011 de 0.013 ed
Control, H20, 13°C 0.011 a 0.018be 0.013 be 0.014 be 0.015
a
Control, H20, RT 0.011 a 0.016 ef 0.013 be 0.016 a
Significance
Preharvest treatment (A) **
Disinfecting +MAP (B) *
Storage temperature (C) *
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, * Nonsignificant or significant at P :$ 0.05. Means within a column followed by the same letter(s) are not
significantly different according to Duncan's multiple range test (P < 0.05). The LSD Value = 0.002, S.E. =
0.001, MSE = 0.001 and e.v. = 0.206.
143
Chapter 4. Tomato Storage (13 'C)
4.3.3.7. Sugar-acid ratio
Table 4.9 shows the sugar-acid (SA) ratio in treated tomatoes varying between 4.34
and 8.41. MAP had a significant effect on the SA ratio. The SA was significantly (P ~
0.001) lower for unpackaged tomatoes stored at room temperature. The packaged
Table 4.9. Changes in sugar-acid ratio of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3 over four
storage times).
Treatment Sugar-acid ratio
DayO Day8 Day 16 Day24 Day 30
ComCat'", Ch, MAP, 13°C 5.545 b 7.118 abe 6.741 ede 7.310 bede 6.388 ede
CorrrCat'", Anolyte, MAP, 13°C 5.545 b 6.623 bede 5.893 ef 8.287 abe 7.437 ab
Comf'at", Ch, MAP, RT 5.545 b 5.51Oef 6.785 ede 8.407 ab
Comf'at'", Anolyte, MAP, RT 5.545 b 5.662 def 6.870 ede 6.146 efg
CorrrCat'", H20, MAP, 13°C 5.545 b 7.695 ab 6.432 def 5.893 fgh 8.279
a
CorrrCat'", H20, MAP, RT 5.545 b 7.282 abc 7.828 abc 9.306 a
ComCat®, H20, 13°C 5.545 b 4.342 f 5.936 def 6.596 edef 6.220 ede
ComCat®, H20, RT 5.545 b 5.283 f 6.509 edef 5.468 gh
Control, Ch, MAP, 13°C 7.226 a 6.089 ede 5.745 ef 6.045 efg 6.155
ede
Control, Anolyte, MAP, 13°C 7.226 a 6.222 ede 6.407 def 6.830 defg 5.813 de
Control, C12,MAP, RT 7.226 a 7.258 abe 7.292 abed 7.799 bed
Control, Anolyte, MAP, RT 7.226 a 6.965 bed 7.299 abed 8.287 abc
Control, H20, MAP, 13°C 7.226 a 6.391 ede 6.792 def 6.055 efg 6.865 abe
Control, H20, MAP, RT 7.226 a 8.288 a 8.379 a 8.280 abc
Control, H20, 13°C 7.226 a 5.364 ef 6.854 ede 6.264 efg 5.332 ef
Control, H20, RT 7.226 a 5.647 def 5.586 efg 5.681 fgh
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC ***
BXC ***
AXBXC ***
NS, *** Nonsignificant or Significant at P ::; 0.001. Means within a column followed by the same
letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The LSD
Value = 1.101, S.E. = 0.101, MSE = 0.465 and C.V. = 0.102.
144
Chapter 4. Tomato Storage (13 'C)
tomatoes stored at l3°C had a higher SA ratio at days 8 and 30 only, compared to
unpackaged ones. The disinfecting + MAP had a significant (P :::;0.001) effect on the
SA ratio, although differences between the disinfecting treatments show no real
conclusive differences.
Storage temperature also had a significant influence on the SA ratio. After 24 days of
storage, the SA ratio was found to be significantly (P :::;0.001) lower in packaged
tomatoes stored at 13°C compared to those stored at room temperature, except in
ComCat® treated tomatoes dipped in anolyte water.
At harvest, green-mature ComCat® treated tomatoes had a significantly (P :::;0.05)
lower SA ratio, when compared to the controls. During the ripening time the SA ratio
generally increased more in ComCat® treated tomatoes, while a general tendency of a
decrease was observed in ripening control tomatoes.
The SA ratio was significantly (P :::;0.001) affected by the interaction between
ComCat® treatment and storage temperature. The two-way interaction between
postharvest treatments (disinfecting, MAP and storage temperature) had a significant (P
:::;0.001) influence on the SA ratio. Similarly, the three-way interaction between the
pre-and postharvest treatment was also highly significant (P :::;0.001) on the changes in
the SA ratio during storage of green mature tomatoes.
4.3.3.8. Ascorbic acid
Table 4.10 displays the changes in ascorbic acid content in ripening tomatoes,
subj ected to different pre- and postharvest treatments, as between 11.10 g.lOO·1 and
23.23 g.100·1. The general tendency observed was an increase in AA during days 8 to
16, followed by a decrease towards the end of storage. MAP seemed to maintain higher
AA contents in tomatoes during storage than unpackaged fruit. Disinfecting treatments
also affected the AA content of tomatoes. Anolyte disinfecting resulted in higher AA
content throughout ripening at both storage temperatures when compared to chlorine
disinfecting and water washing.
145
Chapter 4. Tomato Storage (13 'C)
Table 4.10. Changes in ascorbic acid of tomatoes packaged in Xtend® film or unpackaged and
stored at 13°C and room temperature (RT) for 30 days (n = 3 over four storage times).
Treatment Ascorbic acid {g.IOOg-1FW)
DayO Day 8 Day 16 Day24 Day 30
def
ComCat®, ch, MAP, 13°C 11.580 ab 12.529hij 14.387 16.677
be 16.445bcd
ab a a
ComCat®, Anolyte, MAP, l3°C 11.580 ab 16.116defg 17.520 19.356 23.223
efg 1
ComCat®, Ch, MAP, RT 11.580 ab 17.218 ede 12.733 8.679
abe
ComCat®, Anolyte, MAP, RT 11.580 ab 15.598efg 16.963 16.603
be
ComCat®, H20, MAP, 13°C 11.580 ab 16.826ede 15.933 bed 12.696 fgh 15.716 de
ComCat®, H20, MAP, RT 11.580 ab 22.629a 18.582 a 14.966 ede
ComCat®, H20, 13°C 11.580 ab 19.817b 11.841 fg 12.324 gh 13.181 efgh
ComCat®, H20, RT 11.580 ab 15.427efg 13.832 def 12.715 fgh
Control, Ch, MAP, 13°C 13.868 a 13.895 ghi 14.883 ede 15.635 ede 15.017 der
Control, Anolyte, MAP, 13°C 13.868 a 14.617 fgh 15.598 ed 18.649 ab 18.782
b
Control, Ch, MAP, RT 13.868 a 13.329 hij 10.911 g 11.022 h
Control, Anolyte, MAP, RT 13.868 a 11.107j 13.515 defg 16.454 be
Control, H20, MAP, 13°C 13.868 a 13.626 ghi 12.696 efg 16.112 bed 18.404 be
Control, H20, MAP, RT 13.868 a 11.692 ij 12.869 efg 15.970 ed
Control, H20, 13°C 13.868a 16.951 ede 12.762 efg 13.292 efgh 11.645 h
Control, H20, RT 13.868 a 18.388 bed 14.852 ede 11.748
h
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB *
AXC NS
BXC ***
AXBXC ***
Nonsignificant, *** Significant at P ~ 0.05 or 0.00 I respectively. Means within a column followed by the same
letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The LSD Value =
2.069, S.E. = 0.085, MSE = 1.644 and e.v. = 0.089.
146
Chapter 4. Tomato Storage (13 'C)
Storage temperature significantly (P ~ 0.001) affected the AA content of tomatoes. In
general, higher levels of AA were observed in tomatoes stored at 13°C than at room
temperature. The AA content of tomatoes rapidly increased during the first 8 days, the
fast ripening period, at room temperature, but drops thereafter. At 13°C the AA content
of ripening packaged tomatoes continued to increase up to 24 or 30 days.
The AA content of tomatoes was significantly (P ~ 0.05) affected by the preharvest
ComCat® treatment during storage at 13°C and room temperature. The AA content in
ComCat® treated tomatoes was higher at harvest, although not significantly (P > 0.05),
but remained significantly (P ~ 0.05) higher after most of the postharvest treatments
during storage.
The AA content was significantly (P ~ 0.05) influenced by the interaction between
ComCat® treated and disinfecting + MAP treatments. The AA content of the fruits was
highly (P ~ 0.001) affected by the interaction between the pre- and postharvest
treatments. It was shown that AA content was better maintained in tomatoes during
ripening in low temperature storage, use of packaging and disinfecting treatment as well
as preharvest ComCat® treatments.
4.3.3.9. Peroxidase activity (POX)
The activities of POX were highly (P ~ 0.001) influenced with storage temperature
(Figure 4.4). The general tendency was a decrease in POX up to 8 days of storage,
followed by an increase. In general, a greater level of the activity of POX was observed
for tomatoes stored at room temperature at days 16 to 24, compared to those stored at
13°C. From these data, it seemed as if ripening is delayed by approximately one week
in tomatoes stored at 13°C, compared to those stored at room temperature. The
disinfecting treatment had a highly significant (P ~ 0.001) effect on the POX in
tomatoes, but only the ComCat® treated ones. The activities of POX in ComCat® treated
tomatoes dipped in anolyte water was significantly lower at 16 and 24 days of storage at
13°C, when compared to tomatoes dipped in chlorinated water.
147
Chapter 4. Tomato Storage (13 CC)
»:
." '.r;.. . " .'
,.-... 20
: ~...f.. u,
u
ell -;-Cl)
<l)
en
ell -
~ :ê ~I
8 i
<l) Cl II
0.. 0
"-' 10 ~
--+-- ComCat, Chlorinated, MAP, l3°C • ComCat, Anolyte, MAP, l3°C
_ ... 0 .. · ComCat, Anolyte, MAP, RT -I-- ComCat, Chlorinated, MAP, RT
~Control, Chlorinated, MAP, l3°C _____._ Control, Anolyte, MAP, I3°C
.. -IJ-·· Control, Anolyte, MAP, RT . - -~- .. Control, Chlorinated, MAP, RT
o -----------------
o 10 20 30
Storage titre (days)
Figure 4.4, Changes in peroxidase activity of tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3 over four
storage times),
Significance level showing the effect of pre- and postharvest treatment on changes III
peroxidase activity
Significance
Preharvest treatment (A) ***
Disinfecting (B) ***
Storage temperature (C) ***
AXB ***
AXC *
BXC ***
AXBXC **
NS, *, **, *** Nonsignificant or significant at P ~ 0.01,0.05 or 0.001 respectively. LSDo.o5 Value = i.446, S.E. =
0.027 and e.V. = 0.047.
148
Chapter 4. Tomato Storage (13 'C)
Preharvest ComCat® treatment had a highly significant (P ~ 0.001) effect on the levels
of POX activities during 30 days of storage at 13°C or room temperature. POX activity
was higher in ComCat® treated fruits at harvest. The activity of POX was significantly
(P ~ 0.001) influenced by the interaction between preharvest ComCat® treatment and
disinfecting treatment.
The interaction between storage temperature and disinfecting treatment also had a
highly significant (P ~ 0.001) effect on the changes in levels of POX activity in tomato
fruits. The two-way interaction between preharvest ComCat® treatment and storage
temperature was significant (P ~ 0.05) on the changes in POX activities in fruits during
30 days at 13°C or room temperature. In general, the activity of POX in ripening tomato
fruits in storage was significantly different (P ~ 0.01) due to the three-way interaction
between all the pre-and postharvest treatments.
4.3.3.10. Polygalacturonase activity (pG)
Development of polygalacturonase activities III ComCat® treated and control
tomatoes, stored under different conditions, is shown in Figure 4.5. No PG activity was
detected in green mature tomatoes at harvest, but it changed from 0 to as high as 0.78
nmole minl.g". Storage temperature had a highly significant (P ~ 0.001) effect on the
PG activity in tomatoes. The PG activity was significantly (P ~ 0.001) higher in
tomatoes stored at room temperature up to 24 days of storage.
The PG activity was slightly influenced by the prepackaging disinfecting treatment
during 24 days storage at 13°C or room temperatures. The differences were more
pronounced at 30 days storage at 13°C, than during the earlier periods, where the
activities of PG were higher in tomatoes dipped in chlorinated water than in tomatoes
dipped in anolyte water. The interactive effect of preharvest ComCat® treatment and
storage temperature had a significant (P ~ 0.001) influence on the changes in PG
activity of tomatoes. Similarly, the two-way interaction between disinfecting and
storage temperature had a significant (P ~ 0.05) effect on the PG activity of the
tomatoes.
149
Chapter 4. Tomato Storage (13 'C)
0.8 - ~~ ~_~.. e __ • • __ ee_ --.-
--+-- ComCat, Chlorinated, MAP, 13°C
0.7 • ComCat, Anolyte, MAP, 13°C<
... 0.·· ComCat, Anolyte, MAP, RT
--I-ComCat, Chlorinated, MAP, RT
----4 __ COntrol, Chlorinated, MAP, 13°C
'*' Control, Anolyte, MAP, 13°C
••• !;I.•• Control, Anolyte, MAP, RT
... ~ .. Control, Chlorinated, MAP, RT
O.l ..
0.0
o 5 10 15 20 25 30 35
Storage time (days)
Figure 4.5. Changes in polygalacturonase activities of tomatoes packaged in Xtend®
film or unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3
over four storage times).
Significance level showing the effect of pre- and postharvest treatment on changes III
peroxidase activity
Significance
Preharvest treatment (A) NS
Disinfecting (B) *
Storage temperature (C) ***
AXB NS
AXC ***
BXC *
AXBXC NS
NS, *, *** Nonsignificant or significant at P s: 0.05 or 0.001 respectively. LSDo.o5 Value = 0.073, S.E. = 0.012 and
C.V. = 0.171.
150
Chapter4. Tomato Storage (13OC)
PG activities in tomatoes were not significantly affected by preharvest ComCat®
treatment (Figure 4.5). During the later weeks of storage i. e. at day 30, the PG activities
increased faster in ComCat® treated tomatoes dipped in chlorine supplemented water
and stored at 13°C compared with the PG activities in normal tomatoes subjected to the
same treatments. It was also lower in tomatoes dipped in anolyte water than in those
dipped in chlorinated water.
PG activity remained to be higher in normal tomatoes dipped in anolyte water,
during 20 days at 13°C, compared to the PG activities in ComCat® treated tomatoes
subjected to the same treatments. At 30 days at 13°C, PG activities became slightly
different between ComCat® treated and control tomatoes dipped in anolyte and
chlorinated water.
4.3.4. Microbiological changes
Table 4.11 displays the change in total aerobic bacteria in preharvest ComCat®
treated and control tomatoes subjected to different postharvest treatments. Populations
of aerobic bacteria did not exceed 8.5 10glOCFUg-I during the storage time of 30 days at
either temperature. MAP had a significant effect on the growth of microorganisms on
tomatoes during storage. After 30 days at 13°C, the populations of total aerobic bacteria
were higher in unpackaged treated tomatoes than in packaged ones.
Disinfecting treatments reduced the number of aerobic bacteria significantly (P ~
0.001). During storage, there was a significant difference between the water washed
tomatoes, which had higher aerobic bacteria populations than the disinfected ones. The
populations of aerobic bacteria did not exceed 3.3 10glOCFU g-I in both CorrrCat"
treated and control tomatoes disinfected with chlorinated and anolyte water for 16 days
at 13°C. However, there was no significant difference between the chlorine and anolyte
water dipping treatment.
151
Chapter 4. Tomato Storage (13 'C)
Table 4.11. Changes in total aerobic bacteria populations in tomatoes packaged in Xtend®
film or unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3 over
four storage times).
Total aerobic bacteria (Iogrncfu got FW)
Treatment day 0 Day 8 day 16 day 24 day 30
Comf.at'", Ch, MAP, 13°C 3.076 b <1 kt 1.480 ij 2.154tmn <1 fg
Comf'at'", Anolyte, MAP, 13°C 3.076 b 1.434 hij 1.031 j 2.319 klmn 2.699gh
ComCat®, C12,MAP, RT 3.076 b 3.261 fg 3.425 fgh 3.713 hijk
Comf'at'", Anolyte, MAP, RT 3.076 b 2.300ghi 2.660ghi 3.713 hijk
CornCat®, H20, MAP, 13°C 3.076 b 2.538 ghi 4.672 ede 3.956 hijk 4.628 edef
Cornf'at", H20, MAP, RT 3.076 b 4.092 def 4.009 fgh 6.294 ede
Comf.at'", H20, 13°C 3.076 b 3.066 Igh 5.690 abe 5.900 def 6.994 ab
CornCat ®,H20, RT 3.076 b 5.322 ede 6.357 a 5.539 defg
Control, Ch, MAP, 13°C 5.187a <Ik 1.284 ij 3.261 ijk 1.305 hi
Control, Anolyte, MAP, 13°C 5.187 a <lghi 2.322 hij 2.920jk1m 3.149 ed
Control, ei; MAP, RT 5.187 a 3.483 efg 5.866 abe 5.155 efgh
Control, Anolyte, MAP, RT 5.187a 3.661 efg 5.554 abed 4.325 hijk
Control, H20, MAP, 13°C 5.187 a 3.818 efg 4.814bed 5.200 efgh 5.746 be
Control, H20, MAP, RT 5.187 a 3.644 efg 5.671 abed 8.705 a
Control, H20, l3°C 5.187a 6.350a 5.464 abed 4.447 fghij 7.551 a
Control, H20, RT 5.187 a 6.021 ab 6.156 ab 8.402 b
Significance
Preharvest treatment (A) *
Disinfecting + MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC ***
BXC ***
AXBXC NS
Nonsignificant, *, *** Significant at P ~ 0.05 or 0.001 respectively. Means within a column followed by the
same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The LSD
Value = 1.362, S.E. = 0.161, MSE = 0.712 and e.v. = 0.199.
152
Chapter 4. Tomato Storage (13'(;)
The total aerobic bacteria population was affected by the preharvest ComCat®
treatment (P ~ 0.05). At harvest the population of aerobic bacteria was significantly
lower in ComCat® treated tomatoes, when compared with the controls. Highly
significant interactions (P ~ 0.001) were obtained between the ComCat® treated and
storage temperature, as well as between the disinfection treatments + MAP and the
storage temperature (P ~ 0.001).
Population of moulds and yeasts on tomatoes, as influenced by treatment and time of
storage at 13°C or room temperature, are shown in Table 4.12. Populations of viable
fungi did not exceed 5 10glOCFU g-l during the storage time of 30 days at either
temperature.
MAP suppressed the growth of moulds and yeasts during the first few weeks of
storage. The population of these microorganisms was generally lower in packaged
tomatoes, compared to unpackaged ones during storage at both temperatures. At room
temperature storage, the number of viable moulds and yeasts was significantly lower in
packaged tomatoes than in unpackaged ones during 16 days of storage. However, the
populations in packaged tomatoes started to exceed that of unpackaged fruits after 16
days at room temperature.
The number of viable moulds and yeasts was significantly lower in tomatoes
disinfected in chlorinated and anolyte water, compared to water washed ones, and did
not exceed 1 log.jcfu g-l in both disinfected ComCat® and controls for 16 days at 13°C.
The results showed that disinfecting with anolyte water seemed to be more effective
than chlorinated water, as lower counts of moulds and yeasts were observed, although
significant differences were only observed in the packaged control tomatoes stored at
room temperature.
As a general trend, ComCat® treatment resulted in lower yeast and mould
populations at harvest, a few significant differences were observed during storage,
where this trend was continued. The populations were also significantly (P ~ 0.05)
153
Chapter 4. Tomato Storage (13 CC)
Table 4.12. Changes in yeast and moulds populations in tomatoes packaged in Xtend® film
or unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3 over four
storage times).
Total Fungi Count (log.scfu g" FW)
Treatment day 0 day 8 day 16 day 24 day 30
ComCat®, ei,MAP, l3°C 1.778 ab <li <1 h 1.366 efgh 1.630 edef
gh
ComCat®, Anolyte, MAP, 13°C 1.778 ab <li <lh <l 1.007 fg
ComCat®, ei; MAP, RT 1.778 ab <li 1.952 cdef 2.111 def
ComCat®, Anolyte, MAP, RT 1.778 ab 1.404 efghi 1.842 cdef 1.551 efgh
ComCat®, H20, MAP, 13°C 1.778 ab <l
ghi 3.268 abe 2.491 ede 3.059abe
ComCat®, H20, MAP, RT 1.778 ab <li <1 fgh 4.105 ab
ComCat'", H20, l3°C 1.778 ab <lghi 3.241 abe 2.836 bede 4.214 a
ComCat®, H20, RT 1.778 ab 3.051 abed 3.717 ab 3.551 abe
Control, Ch, MAP, 13°C 2.342 a <1 hi <lgh 1.438 efgh 1.270
efg
Control, Anolyte, MAP, 13°C 2.342 a <1 hi <1 gh <1 gh <lg
Control, Ch, MAP, RT 2.342 a <li 4.152 a 3.439 abe
Control, Anolyte, MAP, RT 2.342 a <li 2.853 bed 1.813 dcfg
Control, H20, MAP, 13°C 2.342 a 1.032 fghi 3.443 ab 3.127 abed 2.928 abed
Control, H20, MAP, RT 2.342 a 1.777 defgh 3.270 abe 4.755 a
Control, H20, 13°C 2.342 a 2.172 edefg 3.453 ab 3.808 abc 4.314 a
Control, H20, RT 2.342 a 4.255 a 4.135a 4.500 ab
Significance
Preharvest treatment (A) *
Disinfecting + MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC *
BXC *
AXBXC NS
NS, *, *** Nonsignificant or significant at P ~ 0.05 or 0.00 I respectively. Means within a column followed
by the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The
LSD Value = 1.270, S.E. = 0.080, MSE = 0.619 and C.V. = 0.3594.
154
Chapter 4. Tomato Storage (13 CC)
influenced by the interaction between storage temperature and ComCat® treatment, as
well as disinfecting +MAP treatments and storage temperature.
The effect of ComCat® treatment and different postharvest treatments on the growth
of total coliform bacteria is shown in Table 4.13. Populations of coliform bacteria did
not exceed 8.3 10glOCFU g-I during the storage time of 30 days at either temperature,
and E. coli was not detected.
The other very important factor affecting microorganism growth and multiplication
is storage temperature. Populations of coliform bacteria in tomatoes were significantly
(P ~ 0.001) affected by the storage temperature. The number of viable coli forms rapidly
increased in tomatoes stored at room temperature. Reducing storage temperature to the
minimum temperature specific for tomatoes, i.e. 13°C, had a positive effect on
controlling them.
Disinfecting treatments reduced the number of coliform bacteria. During storage,
there was a significant difference between the disinfected tomatoes, which had lower
coliform populations than the water washed ones. There was also a difference between
the disinfecting treatments, as chlorine treatment resulted in less coliform development
compared to anolyte treated tomatoes.
The number of total coliforms was influenced (P ~ 0.05) by ComCat® treatment. At
harvest, the number of viable coliforms were significantly lower in ComCat® treated
tomatoes compared to the controls. As a general trend, the population of total coliform
bacteria was found to be lower in ComCat® treated tomatoes, stored at 13°C or room
temp~rature, than in control tomatoes. However, this difference was only significant for
the storage of disinfected tomatoes at room temperature. The population of coliform
bacteria was influenced significantly (P ~'O.OO1) by the interaction between preharvest
treatment and storage temperature. Similarly, there was a significant (P ~ 0.01)
influence of the interaction between disinfecting + MAP and storage temperature on
coliforms. The three-way interaction between pre-and postharvest treatments was also
significant (P s 0.01).
155
Chapter 4. Tomato Storage (13 CC)
Table 4.13. Changes in total coliform populations in tomatoes packaged in Xtend® film or
unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3 over four
storage times).
Total coliform bacteria (log.ecfu g" FW)
Treatment day 0 day 8 day 16 Day 24 day 30
ComCat®, er, MAP, 13°C 2.279 b <lg 1.459 ijk 1.699 ghij 1.100 g
ComCat®, Anolyte, MAP, 13°C 2.279 b 1.176 efg 1.185 ijk 2.001 gh 2.112 ef
ComCat®, Ch, MAP, RT 2.279 b <1fg 1.233 ijk 2.871 fgh
ComCat®, Anolyte, MAP, RT 2.279 b 2.026 defg 3.299 efgh 3.443 efgh
ComCat®, H20, MAP, BOC 2.279 b 1.394 efg 3.875 edef 3.988 ef 5.801 abed
ComCat®, H20, MAP, RT 2.279 b 3.912 abed 3.513 defg 5.677 ed
Comf'at", H20, 13°C 2.279 b 2.693 ede 3.867 ede 3.878 ef 6.711 ab
ComCat®, H20, RT 2.279 b 4.339 abe 6.602 a 7.860ab
Control, Ch, MAP, 13°C 5.293 a <lg <1k 1.688 ghi. 1.295 g
Control, Anolyte, MAP, 13°C 5.293 a <lg 2.682 fghi 2.211 fghi 2.653 f
Control, Ch, MAP, RT 5.293 a 3.649 abed 5.190 abed 4.893 ede
Control, Anolyte, MAP, RT 5.293 a 1.477 efg 5.274 abed 4.047 def
Control, H20, MAP, 13°C 5.293 a 2.921 bede 3.882 edef 5.563 ed 6.223 abc
Control, H20, MAP, RT 5.293 a 3.695 abed 5.396 abe 8.025 a
Control, H20, 13°C 5.293 a 2.496 cdef 4.673 bede 4.940 ede 6.743 a
Control, H20, RT 5.293 a 5.251 a 5.871 ab 8.248 a
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB NS
AXC ***
BXC **
AXBXC **
NS, **, *** Nonsignificant or significant at P ~ 0.00 I respectively. Means within a column followed by the
same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The LSD
Value = 1.475, S.E. = 0.1114, MSE = 0.838 and e.V. = 0.238.
156
Chapter 4. Tomato Storage (13 CC)
4.3.5. Subjective quality analysis
The percentage marketable fruits of tomatoes subjected to different treatments are
shown in Table 4.14. The marketability of tomatoes was significantly higher for
packaged tomatoes than for unpackaged ones stored at both temperatures. Percentage
marketable fruits were significantly affected by disinfecting + MAP treatment. MAP
resulted in 52.4% and 23.8% more marketable control and ComCat® treated tomatoes
during the 16 days of storage at room temperature respectively. Similarly, there were
29.7% and 40.3% more marketable ComCat® treated and control tomatoes after 30 days
at 13°C respectively. Disinfecting helped to protect the tomatoes, as water washed
tomatoes started to deteriorate, from 8 days on, at room temperature, and 16 days at
13°C, compared to disinfected ones.
Storage temperature had a strong influence on the marketability. Marketability of
tomatoes stored at room temperature started to decrease from 16 days on, while at 13°C,
the tomatoes lasted at least for 24 days.
ComCat® treatment did not seem to have much of an effect on the marketability of
tomatoes, when compared to the controls. However, it could be interpreted that the
onset of senescence is postponed in ComCat® treated tomatoes, as unpackaged control
tomatoes, that were not disinfected, were only 50% and 33.3% marketable after 8 and
16 days storage at room temperature, compared to the 74.6% and 64.8% of the
ComCat® treated ones. An almost similar trend is observed for packaged, water washed
ComCat® treated tomatoes stored at room temperature.
The two-way interaction between preharvest treatment and disinfecting + MAP had a
significant (P ::;0.01) influence on the changes in percentage marketable fruit during 30
days storage at 13°C or room temperature. The percentage marketable fruits were
significantly (P ::; 0.01) affected by the interaction between preharvest treatment and
storage temperature.
157
Chapter 4. Tomato Storage (13 "C)
Table.4.14. Changes in percentage marketability of tomatoes packaged in Xtend®
film or unpackaged and stored at 13°C and room temperature (RT) for 30 days (n = 3
over four storage times).
Treatment Percentage marketable fruits
DayO Day8 Day 16 Day24 Day30
ComCat®, ei; MAP, 13°C 100a 100 a IOOa 9l.7c 9l.5
b
CorrrCat'", Anolyte, MAP, 13°C IOOa IOOa 100 a 95.8 b 95.8 a
ComCat®, ei; MAP, RT IOOa IOOa 94 b 72.2 f
Cornï.at", Anolyte, MAP, RT IOOa 100a 95.2 b it»:
ComCat®, H20,MAP, 13°C 100 a 100a 100a 90.5 ed 8l.0
g
CorrrCat'", H20, MAP, RT 100 a 90.5 cd 88.6
e 64.4h
.CorrrCat'", H20, 13°C IOOa IOO
a 82.2 g 55.0i 51.3 e
Cornf.at'", H20, RT IOOa 74.6 f 64.8 h
Control, Cb, MAP, 13°C 100a 100a 100 a 100a 89.9c
Control, Anolyte, MAP, 13°C 100 a IOOa IOOa IOOa 91.7b
Control, Ch, MAP, RT IOOa 95.8 b 90.6 cd 68.6g
Control, Anolyte, MAP, RT 100a IOOa 95.8 b 72.6c
Control, H20, MAP, 13°C IOOa IOOa IOOa 90.4 ed 81.4 d
Control, H20, MAP, RT IOOa 84.ge 85.7 f 53.6
k
Control, H20, 13°C IOOa 100 a 63.3 i 54.0j 41.1 f
Control, H20, RT IOOa 50g 33.3
j
Significance
Preharvest treatment (A) *
Disinfecting +MAP (B) ***
Storage temperature (C) ***
AXB **
AXC **
BXC NS
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P s: 0.05,0.01 or 0.001 respectively. Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple
range test (P < 0.05). The LSD Value = 1.332, S.E. = 1.011, MSE = 60.111 and e.V. = 0.099.
158
Chapter 4. Tomato Storage (13 'C)
4.4. Discussion
The quality that fresh produce has at harvest can be extended by a variety of
postharvest processes, such as MAP (Ballantyne et al., 1988a and b; Zagory and Kader,
1988; Geeson, 1988; Salunkhe et al., 1991; Exama et al., 1993; Jeon and Lee, 1999;
Seyoum et al., 2001). The results of this chapter show that MAP ;lth microperforated .~<~
Xtend® film not only resulted in normal respiration of tomatoes, but also reduced
moisture loss from the produce, and therefore effectively reduced (P ~ 0.001) PWL
(Table 4.1). This is in agreement with previous findings that the medium or least
permeable film maintains the moisture in packages at a proper level during storage
(Howard and Hernandez-Brenes, 1997; Jeon and Lee, 1999). Condensation is also
prevented by this material, thus preventing microbial growth due to high relative
humidity (Zagory and Kader, 1988).
The 02 utilisation by the tomatoes was faster during the first 3 days of storage at
13°C as well as room temperature. This pattern was similar to that previously described
for many packaged fruits and vegetables (Henig and Gilbert, 1975; Rizvi, 1981; Smith
et al., 1987; Carlin et al., 1990). During MAP, O2 and CO2 concentrations remained
above 15% and below 6% in microperforated Xtend® film during storage, respectively
(Fig. 4.1 and 4.2), suggesting that there was normal respiration of tomatoes during the
storage period (Exarna ef al., 1993; Jeon and Lee, 1999). Although, the modified
atmosphere created by microperforated Xtend® film did not excessively reduce O2 and
increase C02 levels, the data clearly show that the metabolic activity was retarded due
to MAP when compared to unpackaged fruit. The greater level of free sugars (sucrose,
glucose and fructose) showed this in packaged tomatoes stored at 13°C, as well as room
temperature (Tables 4.5 (a - c), 4.6 and 4.7). Since free sugars are substrates for
respiration, MAP had a significant effect on reducing the glucose utilisation by up to
25.5% and 11.2%, during storage at room temperature and 13°C, respectively, when
compared to the glucose content of unpackaged tomatoes. The fructose and total soluble
159
Chapter 4. Tomato Storage (13 CC)
sugar contents were also maintained better in both packaged, ComCat® treated and
control tomatoes stored at these storage temperatures (Tables 4.5 (c) and 4.6).
MAP also resulted in the preservation of quality attributes such as AA content. After
24 days at room temperature the AA was 15.0% and 26.4% more in packaged ComCat®
treated and control tomatoes respectively (Table 4.10). Similarly, the AA retention was
16.1% and 36.7% more in packaged ComCat® treated and control tomatoes stored at
l3°C for 30 days, respectively. The modified atmospheres created by Xtend® film
delayed the ripening of tomatoes, and the AA increased with ripening during storage.
This is in agreement with similar findings reported by Geeson et al. (1985), Howard and
Hemandez-Brenes, (1997), Batu and Thompson (1998) and Saito et al. (2000).
Although least permeable packaging might be preferred to reduce microbial growth
(Batu and Thompson, 1994), MAP with high permeability was reported to be
significantly protective (Exama et al., 1993; Batu and Thompson, 1997; leon and Lee,
1999; Seyoum et al., 2001). The current results showed that the population of total
aerobic bacteria, molds, yeasts and total coli forms were generally found to be less in
packaged tomatoes than in unpackaged tomatoes stored at 13°C, as well as room
temperature (Tables 4.11 - 4.13), although some discrepancies were observed during
some storage intervals.
Storage temperature was the most important factor affecting the postharvest quality
and shelf life of tomatoes. All quality parameters tested, except SH ratio, were
significantly (P ~ 0.001) influenced by the storage temperature. The changes in SH ratio
was generally not an important parameter of the quality characteristics of tomatoes
(Table 4.8), but changes in SA ratio was more important in explaining the changes in
quality characteristics in tomatoes subjected to different postharvest treatments (Table
4.9). With increasing temperature, the headspace concentrations of oxygen decreased,
while carbon dioxide increased rapidly (Fig. 4.1 and 4.2). Before equilibration, the
concentrations of O2 decreased up to 5 and 12 days in packages of tomatoes stored at
room temperature and l3°C, respectively. Similarly, the CO2 concentrations increased
160
Chapter 4. Tomato Storage (13 'C)
up to 5 and 12 days in the headspace of packages of tomatoes stored at room
temperature and 13°C, respectively, after which equilibrium was attained. This would
indicate that at higher temperature the metabolism in tomatoes was enhanced and the
utilisation of 02 increased with subsequent production of C02. Varoquaux and Wiley
(1994) reported similar findings. Lowering the storage temperature therefore reduces
the respiration, and delays senescence, while high temperature storage hastened the
senescence oftomatoes (Table 4.1 - 4.14).
The changes in moisture content, TTA, pH, TSS, free sugars, AA, microbiological
and enzyme activity occurred at substantially faster rates in tomatoes stored at room
temperature than in tomatoes stored at 13°C. Storage at 13°C resulted in a substantial
decrease in PWL of tomatoes compared with fruits stored at room temperature (Table
4.1). High temperature increases the vapour pressure difference between the product
and the surrounding air, which is the driving potential for faster moisture transfer from
tomatoes to the surrounding air (Ryall and Lipton, 1979; Ryall and Pentzer, 1982;
Kader et al., 1985; Salunkhe et al., 1991; Cantwell et al., 1992).
There was a faster increase in the pH and a decrease in TTA of tomatoes stored at
room temperature, compared to fruits stored at 13°C (Table 4.2 and 4.3). The increase
in pH of tomatoes at room temperature with increased storage time was in agreement
with the previous findings by Mohammed et al (1999), but also contrary to the findings
reported by Came and Zilva (1949). After 24 days of storage, the AA content was better
retained in tomatoes stored at 13°C compared to those stored at room temperature
(Table 4.10). The AA content and pH values of tomatoes were increasing while the
TTA ·content was decreasing in tomatoes during ripening and storage. Mohammed et al.
(1999) reported a similar relationship in the changes in AA content, pH values and TTA
of tomatoes during ripening in storage at 20°C. In general, the rapid increase in pH,
decrease in TTA and depletion of AA in tomatoes stored at room temperature could be
attributed to the enhanced metabolism, ripening and senescence of these tomatoes
compared to those stored at 13°C. Higher nutritional values in terms of higher AA
161
Chapter 4. Tomato Storage (13 'C)
content of tomatoes stored at 13°C for 30 days was evident from these data (Table
4.10). The AA content generally increased with ripening in tomatoes during 30 days of
storage at 13°C. However, at room temperature the AA rapidly increased within 8 to 16
days of ripening and showed a decline after full ripeness of tomatoes. This trend was in
agreement with previous data that AA content increased with ripeness (Brecht et al.,
1976; Mohammed et al., 1999), however, Watada et al. (1976) observed no change in
AA content with ripeness.
The TSS oftomatoes was better maintained at 13°C than in tomatoes stored at room
temperature (Table 4.4). The higher rate of increase in TSS of some of the tomato
samples stored at room temperature was due to excessive moisture loss (Table 4.1) as
well as the hydrolysis of carbohydrate to soluble sugars.
The utilization of free sugars was faster in tomatoes stored at room temperature,
compared to those stored at 13°C (Tables 4.5 (a - c) and 4.6), which could be ascribed
to the reduced respiration and metabolism at 13°C. Reducing sugars, such as glucose,
are the main substrates in the respiration process to produce energy required in the
metabolism of fruit. It was calculated that in green mature tomatoes, 73% of glucose
degradation took place through the Embden-Meyerhof processes and 27% through the
alternative oxidative path way, which functions mainly as a mechanism for the
conversion of glucose to various intermediates for biosynthesis and possibly, to provide
NADPH2 for this process (Wang et al., 1962, in Hobson and Davies, 1971). The
observed changes in gas compositions therefore match this relationship to metabolic
activity .
. Changes in metabolic activity can also be monitored by enzyme activities, since
enzyme activities govern most of the chemical and physical effects that occur during
ripening of fruit. For instance, the loss of firmness of tomatoes during ripening and
storage is due to the increased activity of PG in tomatoes (Hobson, 1965; Brady et al.,
1987). The activities of POX and PG were higher (P :::;0.001) in ripening tomatoes
162
Chapter 4. Tomato Storage (13 'C)
stored at room temperature than in tomatoes stored at 13°C (Fig. 4.4 and 4.5). Similar
results were reported by Mattoo et al., 1975 and Salunkhe et al., 1991.
Storage at room temperature, in part, created conditions that are favourable for the
growth of microorganisms especially during early stages of storage (Table 4.11 - 4.13).
The physical or biochemical characteristics of the fruit may influence the type and
populations of microorganisms, which develop on fresh produce (Brackett, 1990), but
this was not investigated in the current study. The activity of PG increased in tomatoes
stored at room temperature, compared to those in tomatoes stored at 13°C (Fig. 4.5),
and resulted in a loss of firmness of the fruit. Thus, higher storage temperature, the
availability of water-soluble, free sugar, and moisture creates conditions favourable for
the proliferation of microorganisms in tomatoes. The rapid decrease in TTA in tomatoes
stored at room temperature (Table 4.3) could also partially contribute to the greater
growth of microorganisms in tomatoes stored at room temperature. Gould (1983)
considered fruit acidity as a major postharvest factor affecting the keeping quality of
. tomatoes. Mohammed et al. (1999) supported this view that the higher TTA could
protect fruit from fungal infection. In this study, the fact that the data showed that TTA
of tomatoes stored at room temperature decreased faster (Table 4.3), could in part,
contribute to the greater growth of microorganism in tomatoes stored at room
temperature.
The percentage marketable fruit were lower (P ~ 0.001) for tomatoes stored at room
temperature compared to those stored at 13°C (Table 4.14). The percentage marketable
tomatoes was 33.3% and 64.8% for unpackaged control and ComCat® treated tomatoes
stored at room temperature for 16 days respectively. After 24 days at room temperature
the percentage marketable fruits varied from 53.6% - 77.9% for both ComCat® treated
and control tomatoes. However, the percentage marketable fruit ranged from 81.0 -
95.8% in packaged tomatoes stored at 13°C for 30 days. These results thus
demonstrated the overall effect of temperature on the quality of tomatoes during
163
Chapter 4. Tomato Storage (13'C)
ripening and storage. The observed differences between control and ComCat® treated
tomatoes is discussed separately.
Chlorine solution and anolyte water are disinfecting agents and were used to control
microorganisms. The use of chlorine is well studied and described. It was reported that
chlorine treatment at 200 ppm reduced the population of pathogens by 0.35 to 3 log
CFU cm -2 in tomatoes (Beuchat et al., 1998 and Ukuku and Sapers, 2001). In the
current study, chlorinated water dipping treatment for 20 minutes significantly reduced
the populations of total aerobic bacteria, moulds and yeasts, and total coliforms,
compared to the populations in water washed tomatoes (Tables 4.11 - 4.13). However,
the effectiveness of chlorine treatment decreased when tomatoes were stored at room
temperature. These findings were similar to those reported by Ukuku and Sapers (2001),
that the effectiveness of chlorine treatment diminished with increase in temperature and
storage time. The anolyte water reduced (P ~ 0.001) and suppressed the growth of total
aerobic bacteria, molds, yeasts and total coliform bacteria in tomatoes during storage as
effectively as chlorinated water (Tables 4.11 - 4.13). It was also shown that 5 minutes
dipping in anolyte water was sufficient for desirable control of microorganisms. The
main reason for this is that the anolyte water contains freely available radicals (see
Chapter 2), which are immediately available for action on the microorganisms, whereas
in the case of chlorinated water these radicals are not freely available, and are formed
slowly. As a result, anolyte water was found to be an effective method in controlling
postharvest decay through killing and suppressing growth of total aerobic bacteria,
moulds and yeasts, and total coliform bacteria during tomato storage for 30 days at
13°C as well as 24 days at room temperature.
The advantages of anolyte water above chlorine treatment were not only restricted to
control of microorganisms. During the early active ripening period of tomatoes, the
lowest O2 and highest CO2 concentrations were found in packages of tomatoes dipped
in chlorinated water, compared to those dipped in anolyte, and those washed with water
(Figures 4.1 and 4.2). These results thus suggested that the tomatoes dipped in
164
Chapter4. Tomato Storage (13'C)
chlorinated water had higher rates of respiration and metabolism than tomatoes dipped
in anolyte water, or those washed with water. The loss of moisture was generally higher
in tomatoes dipped in chlorinated water than in anolyte water (Table 4.1). This could be
attributed to the effect of chlorine solution on the skin of tomatoes and surface tissue. It
was observed that chlorinated water dipping treatment generally left a taint on the
surface of tomatoes, while the surface of tomatoes dipped in anolyte water remained to
be very shiny during the 30 days of storage at 13°C. These results thus implied that
chlorinated water might not be the optimum treatment for tomatoes, because it affects
tomatoes by causing some stress condition.
Other differences in quality parameters between chlorine and anolyte water
disinfected tomatoes are as follows. The TSS content was generally maintained better in
tomatoes dipped in anolyte water than in tomatoes dipped in chlorinated water (Table
4.4). The other interesting point was that the fructose content increased continuously in
tomatoes dipped in anolyte water for up to 24 days while it increased only up to 16 days
in tomatoes dipped in chlorinated water during storage at 13°C (Table 4.5 (c)). The
ComCat® treated tomatoes dipped in anolyte water also performed well in maintaining
the total sugar content. The total sugar content was 9.6% and 6.0% more after 24 and 30
days storage at 13°C respectively, although the total soluble sugar was lower during
early ripening due to delayed ripeness. It seemed that the overall physical and chemical
characteristics of tomatoes dipped in anolyte water had an effect on the microbiological
flora during storage at 13°C. At this optimum storage temperature for tomatoes, the
population of microorganism was suppressed better in tomatoes dipped in anolyte water
(Tables4.11-4.13).
The level of activity of POX seemed to be slightly higher in tomatoes dipped in
chlorinated water than in those dipped in anolyte water. The POX activity level in
tomatoes dipped in anolyte water generally remained lower up to days 16 at 13°C. The
overall effect of these quality parameters on the tomatoes dipped in anolyte water
165
Chapter 4. Tomato Storage (13 'C)
improved the percentage marketable fruit to the same extent as chlorinated water, and
better than those washed in water (Table 4.14).
The combined effect of disinfecting and packaging is discussed next. Disinfecting +
MAP had a significant effect on the postharvest quality parameters tested (Tables 4.1 -
4.6 and 4.14), except on the sucrose content, which is actually very low in tomatoes
(Table 4.5 (a)). The effectiveness of microperforated packaging film increased when
combined with a prepackaging disinfecting treatment. The main advantage of
microperforations is that it allows gas dynamics to create optimum gas composition
specific to each fruit and vegetables. However, at relatively higher O2 and lower CO2
level, the growth of microorganisms could not be suppressed, due to low C02
concentration. In this study, the prepackaging disinfecting treatment seemed to solve the
problem of microorganisms and maximise the effectiveness of the modified atmosphere,
created by the microperforated film during storage of tomatoes. These results thus
showed that the coupled effect of disinfecting treatment and MAP was highly
significant (P ~ 0.001) on the population of total aerobic bacteria, moulds and yeasts,
and total coliforms in tomatoes (Tables 4.11 - 4.13).
Similarly, the interaction between disinfecting treatment + MAP and storage
temperature had a significant effect on gas concentrations, PWL, pH, TTA, TSS,
sucrose and glucose contents, SA ratio, AA content, and POX and PG activity of
tomatoes (Fig. 4.1 - 4.5, Tables 4.2 - 4.5 (b), 4.9 and 4.10).
The effect of ComCat® on postharvest quality and shelf life of tomatoes was
investigated under different postharvest treatment practices. Directly after harvest the
ComCat® treated tomatoes differed from the control tomatoes in having a lower pH,
lower contents of AA, glucose and fructose, total soluble sugar, sucrose equivalent, SA
ratio, natural microbial populations and higher TTA, TSS, POX activity and sucrose
content.
This treatment also had an effect on some of the quality parameters during storage.
The O2 and N2 concentrations, PWL, pH of tomatoes, TSS, fructose, glucose, sucrose
166
Chapter4. Tomato Storage (13CC)
and total sugar contents, sucrose equivalent, SH ratio, SA ratio, AA content, peroxidase
activity, populations of total aerobic bacteria, moulds and yeasts, total coliform bacteria,
and marketability were significantly affected by the ComCat® treatment. However, the
preharvest ComCat® treatment had no significant effect on titratable acidity and PG
activity in tomatoes.
Although the differences in gas concentrations (02, CO2 and N2) in the headspace of
packages were not clear for storage at optimum temperature (13°C), the differences
were highly significant in packages of ComCat® treated and control tomatoes stored at
room temperature (Fig. 4.1 - 4.3). The small difference in O2, CO2, and N2
concentrations in packages of ComCat® treated and control tomatoes stored at 13°C
suggest that at this storage temperature, both products had similar respiration and
metabolism rates. However, during storage at room temperature, the air in the
headspace of ComCat® treated tomatoes had higher O2, lower CO2 and lower N2
concentrations than the micro atmosphere in the packages of control tomatoes. This
indicates that control tomatoes had a higher rate of respiration, utilising more O2 and
releasing more CO2 at room temperature than the ComCat® treated ones.
The pH of tomatoes was highly influenced by preharvest treatments. Directly after
harvest, the pH of green mature ComCat® treated tomatoes was lower than in normal
tomatoes. The pH of tomatoes increased with increasing ripeness, supporting the results
of Mohammed et al., (1999). The changes in pH of tomatoes were highly dependent on
the storage temperature and stage of ripeness. There was a greater increase in pH in
control tomatoes stored at room temperature than in ComCat® treated tomatoes (Table
4.2), which could be due to a different rate of metabolism.
The TTA of ComCat® treated tomatoes was greater (P ~ 0.001) than that of control
tomatoes at harvest (Table 4.3). According to Mohammed et al. (1999) a higher fruit
acidity is an advantage, which causes a lower incidence of fungal infection. The effect
of ComCat® treatment was not significant on the TTA during storage.
167
Chapter 4. Tomato Storage (13 'C)
Although not significant at P < 0.001, the TSS content was slightly higher in
ComCat® treated tomatoes at harvest, but in general, the TSS seemed to be maintained
better in the ComCat® treated tomatoes during storage at both temperatures (Table 4.4).
After 24 days at room temperature the TSS was 8.55% higher in unpackaged ComCat®
treated tomatoes than in unpackaged controls. This would also be an indication that, at
room temperature, ComCat® treated tomatoes had a lower respiration rate, and hence
experienced a delayed senescence. Although the AA content was slightly less in
ComCat® treated tomatoes at harvest (Table 4.10), it increased more in ComCat®
treated tomatoes during storage at 13°C up to 30 days. The AA content was 8.7% and
19.1% more in ComCat® treated tomatoes disinfected in chlorinated and anolyte water
after 30 days at 13°C respectively, when compared with controls.
The contents of TSS, glucose, fructose, total sugar and sucrose equivalent were not
significantly affected at P < 0.001 by the preharvest ComCat® treatment. At harvest, the
ComCat® treated tomatoes had slightly higher sucrose concentrations, but it remained
lower in ComCat® treated tomatoes during storage (Table 4.5 (a)). The fructose content
was also lower in ComCat® treated tomatoes at harvest and during the early stages of
storage, but increased with ripeness to maximum levels at days 16, 24 and 8 in
ComCat® treated tomatoes dipped in chlorinated, anolyte and distilled water
respectively. Maximum levels of control tomatoes were respectively 8 days earlier for
the disinfected ones, but the same for the water washed tomatoes. This may indicate that
the ripening process (climacteric peak) was delayed in ComCat® treated tomatoes by
almost one week. The fructose content decreased after these mentioned days, but
remained to be higher in ComCat® treated tomatoes than in controls. At room
temperature storage, the fructose content consistently remained lower in ComCat®
treated tomatoes than in controls. The lower free sugar content associated with
ComCat® treated tomatoes could also be an indication of lower respiration and
metabolism rates, supporting the same deduction made for the headspace gas dynamics
(Fig. 4.1 - 4.3). However, during the later stages of ripening, and in ripe ComCat®
168
Chapter 4. Tomato Storage (13 CC)
treated tomatoes, these sugars began to accumulate. Normally, free sugars decrease
faster if there is a high respiration rate, since respiration in plants involves the oxidative
metabolism of sugars and organic acids to end products, CO2 and H20 with the
simultaneous production of energy (Varoquaux and Wiley, 1994). The decline in
reducing sugar does not continue until the end of storage in ComCat® treated tomatoes
and there was no correlation with the headspace gas dynamics, which would suggests
that the lower free sugar content in ComCat® treated tomatoes may not be related to the
respiration process, but could be attributed to the effect of the plant growth hormones
(i.e. gibberellin) in ComCat® that delayed the ripening of the fruit. Such correlations
were reported by Salunkhe et al. (1975), Stallknecht et al. (1983) and Bartholomew et
al. (1983).
The activity of POX was higher in ComCat® treated tomatoes at harvest. In this
context, increased POX activity in tomatoes is thought to be responsible for increasing
resistance to pathogenic infection, at least in part (Khripach et al., 1997). This could
support the results in Table 4.11 - 4.13 where lower counts in microorganisms are
shown to occur on ComCat® treated tomatoes. The proposed mechanism for higher
resistance against microorganisms is explained by the findings of previous researchers,
who showed that ComCat® treatment induces POX, chitinase and pl-3 gluconase,
which are enzymes that protect cell walls and prevent infection (Schnabl et al., 2001;
Hiister, 2001). However, during storage and ripening, the activities of POX in ComCat®
treated tomatoes were found to remain significantly (P ~ 0.001) lower for 30 days at
13°C, compared to the activities of POX in control tomatoes. Previous findings
indicated that decompartmentation, a consequence of senescence due to chilling (Parkin
et al., 1989; Palma et al., 1995), may lead to the increase in extractable POX activity.
Therefore, the lower levels of POX activity in ComCat® treated tomatoes may indicate
that this product has a better postharvest quality with lower oxidation and ripening
related processes during ripening and storage (Thomas et al., 1981). It could be that
169
Chapter 4. Tomato Storage (13 'C)
differences in fruit ripeness, as indicated by the sugar contents (Table 4.5 and 4.6),
resulted in differences in POX activity between ComCat® treated and control tomatoes.
The PG activity in tomatoes has a positive correlation with the firmness of fruits
(Foda, 1957; Hobson, 1965; Brady et aI., 1987). High PG activity in tomatoes would
therefore imply loss of firmness. This enzyme activity increased in all tomatoes during
storage, which was in agreement with results of other researchers (Tucker et al., 1980;
Brady et al., 1982; Tucker and Grierson, 1982; Yoshida et al., 1984). The preharvest
ComCat® treatment had no effect on PG activity during the first three weeks of storage
(Fig. 4.5). Although not significant (P > 0.05), PG activities were slightly higher in
control tomatoes during the first week of ripening, compared to ComCat® treated
tomatoes, when stored at l3°C. The greatest difference between the ComCat® treated
and control tomatoes in PG activity was only visible after 30 days at 13°C. This is in
agreement with the work of Lampe (1971), who showed that PG was low during the
first two or three weeks of storage of tomatoes, but not in the later stages, and ascribed
this inhibition to indol-acetic-acid, which is one of the major constituents of Comf'at'",
At harvest, the population of aerobic bacteria, moulds and yeasts, and total coliform
bacteria were significantly lower in ComCat® treated tomatoes. These results were in
agreement with the previous hypothesis on the preharvest performance of ComCat®
treated products in terms of levels of photogenic infections (Schnabl et al., 2001). A
reduction of plant disease symptoms up to 45% in comparison to untreated control
plants has been reported by these researchers. It seems as if the low pH, low soluble
sugar content, higher titratable acidity and higher POX activity of ComCat® treated
tomatoes may therefore contribute to the lower microbial populations at harvest.
During the early stages of tomato ripening in storage at 13°C, the population of total
aerobic bacteria, moulds and yeasts seemed to be lower in ComCat® treated tomatoes
disinfected in chlorinated and anolyte water than in control tomatoes. The populations
of total aerobic bacteria were significantly higher in unpackaged control tomatoes than
in unpackaged ComCat® treated ones, both stored at room temperature. The lower
170
Chapter 4. Tomato Storage (13 'C)
soluble sugar content (Tables 4.5 and 4.6), lower pH (Table 4.2), higher TTA (Table
4.3) and higher POX activity (Fig. 4.4) in ComCat® treated tomatoes during the early
ripening period could be partially the reason for the reduced population of
microorganisms. The importance of fruit acidity, as a major factor affecting the keeping
quality of tomatoes, has been examined by Gould (1983). The results in the current
study support these findings, since the higher titratable acidity of ComCat® treated
tomatoes at harvest could explain the lower incidence of microbial infection, compared
to the untreated controls. Thome and Alvarez (1982), as presented by Mohammed et al.
(1999), have examined the importance of titratable acidity of tomato cultivars, and
suggested that higher TTA protect fruit from microbial infection. The availability of
more free sugars (Tables 4.5 and 4.6) and higher POX activity in control tomatoes
created, in part, conditions more favourable for microbiological flora. However, the
populations of microorganisms seemed to increase in some of the ComCat® treated
tomatoes during the later stages of storage. This is in positive correlation with the free
sugar content in ComCat® treated tomatoes. For example, the fructose concentrations
increased more in ComCat® treated tomatoes after two weeks of storage and may be
responsible for the proliferation of microorganisms in some samples of ComCat®
treated tomatoes. In general, there was no significant difference between ComCat®
treated and control tomatoes in populations of moulds and yeasts, and total coliform
after 30 days at 13°C. The total aerobic bacteria, however, were lower (P :::;0.05) in
ComCat® treated tomatoes.
The high quality attributes of ComCat® treated tomatoes during storage were shown
by the percentage marketable fruits (Table 4.14). The overall visual appearance of
ComCar" treated tomatoes was better than the control during storage, even at room
temperature.
The results that ComCat® treated tomatoes were superior to the controls, in many
cases at room temperature storage, was indicated by the two-way interaction between
preharvest ComCat® treatment and storage temperature which was highly significant (P
171
Chapter 4. Tomato Storage (13 CC)
~ 0.001) on gas concentrations, changes in pH, sucrose content, TSS, AA content,
microbiological flora and marketability of tomatoes during storage. Lower metabolism
at room temperature in ComCat® treated tomatoes contributed to the conservation of
better quality at room temperature storage. Otherwise, storage at 13"C was the optimum
storage temperature for both ComCat® treated and control tomatoes, and made the
differences in quality attributes more complex.
To summarise, the results in this chapter showed that chlorine treatment may not be
the optimum disinfectant, as is generally accepted. Other alternatives should be
investigated. The anolyte water used here showed to be a promising candidate in saving
time, having less eftect on the fruits and being environmentally friendly. Preharvest
ComCat® treatment not only improved crop yield, as was found in previous work by
other researchers, but resulted in better keeping quality of fruit e.g. tomatoes. Benefits at
13"C storage were:
1) offers a new strategy for preharvest plant protection and strong
produce at harvest
2) better microbiological quality in terms of less population of total
aerobic bacteria, molds, yeasts and total coliform
3) better nutritional quality in terms of higher AA content at full
ripeness
4) better shelflife at }3°C due to a delayed senescence
Further benefits on the shelf life at room temperature storage, being:
1) lower respiration (high 02, low CO2, and low N2) and delayed
senescence
2) better chemical quality in terms of higher TSS content, and lower pH
3) accumulation of fructose towards the last two weeks of storage
4) higher total soluble sugar and SH ratio
5) better microbiological quality in terms of lower total aerobic bacteria,
molds, and yeast populations
172
Chapter 4. Tomato Storage (13 'C)
The findings that ComCat® treated tomatoes showed better storage performance than
untreated controls, not just at 13°C, but also at room temperature, opens the possibility
to investigate the storage performance of these tomatoes at temperatures higher than the
optimum storage temperature of 13°C, but under controlled conditions. Such controlled
temperatures can be achieved in an evaporative cooling chamber. The results of such
research are presented in Chapter 6.
173
CHAPTERS
EFFECT of PREHARVEST TREATMENT and
FORCED VENTILATION EVAPORA TIVE
COOLING on CARROTS
Abstract
A forced ventilation evaporative cooling (EC) system was designed and developed in
which the temperature could be reduced by 8.4 - 13.4°C below ambient temperature,
with a rise of relative humidity up to 91%. Storage in this EC resulted in increased
shelf lives of both ComCat® treated and control carrots from 4 to 24 days, compared to
storage at ambient conditions. Preharvest ComCat® treatment significantly (P :s 0.05)
affected pH, total sugar content and the population of moulds and yeasts in carrots
during storage at EC. MAP significantly (P :s 0.001) reduced physiological weight loss,
moisture, and juice content of carrots stored inside EC. MAP coupled with evaporative
cooling reduced the rate of sugar utilization for metabolic activities, compared to
unpackaged carrots stored at ambient conditions. The populations of aerobic bacteria
and fungi were significantly (P:S 0.001) affected by MAP coupled with EC temperature.
Disinfecting with chlorinated helped additionally to limit microbial growth during EC
storage.
5.1. Introduction
Ethiopia has a wide variety of climatic and soil types that can enable it to produce
crops for both home consumption and the export market (Agonafir, 1991). Agriculture
is the mainstay of the economy, with vegetable production around 2.86 million tons.
Ninety five per cent of the total volume of horticultural products is fresh vegetables.
There is a need for high crop yield in Ethiopia to feed its increasing population, but due
to a lack of agricultural input, such as fertilizers, the production of vegetables is low and
174
Chapter 5. Carrot storage (EC)
fully dependent on traditional farming systems. Postharvest handling of vegetables is
also poor.
Presently, small plots with farmers do not have the capacity to consistently buy
agrochemieals for boosting their production. ComCat® has been developed and used to
increase agricultural production of crops by more than 20% (Schnabl et al., 2001;
Huster, 2001). It could be an alternative to other agrochemicals, as it is required in low
doses. It is also environmentally and ecologically friendly.
There are very few modem means of transportation, storage, and processing of fresh
vegetables in the Ethiopia. This is one of the reasons for high postharvest losses that the
country is experiencing. Wolde (1991) pointed out the necessity of government
involvement in the improvement of packaging, cold storage, grading and transportation
facilities, in order to maintain quality of vegetables for markets both local and abroad.
In chapter 3 and 4 it was shown that ComCat® treated vegetables performed better
after harvest than untreated controls, even at temperatures above that of the
recommended storage temperatures of specific vegetables. It was therefore decided to
investigate the postharvest performance of ComCat® treated vegetables at a controlled
temperature that is higher than the optimum storage temperature. A storage facility,
which is suited for use in a developing country, would be used for this purpose. The aim
of the work in this chapter is, therefore, to investigate the postharvest qualities of
ComCat® treated carrots stored in a low-cost evaporative cooling chamber at
temperatures between 16°C and 22°C, and relative humidity of 78%-91 %.
The objectives of the study are:
1. to investigate the effectiveness of forced ventilation EC in reducing temperature and
increasing relative humidity during storage of carrots;
2. to investigate the storability of preharvest ComCat® treated carrots usmg EC
methods;
3. to explore the synergistic effect of pre-packaging treatments (disinfecting m
chlorinated water) when combined with MAP and EC storage.
175
Chapter 5. Carrot storage (EC)
5.2. Materials and methods
5.2.1. Evaporative cooling chamber
In earlier work, a naturally ventilated EC was designed and constructed using locally
available and low cost materials (Seyoum and W/Tsadik, 2000). That cooler was able to
reduce the storage temperature relative to the surrounding air temperature at the study
site of Alemaya University, Ethiopia. Using these results as a starting point, and with
the objective to further reduce the temperature as well as increase the relative humidity
of the air, a forced ventilation evaporative cooler was designed and constructed for
vegetable storage. Fig. 5.1 shows a schematic diagram of the EC. The cooler consists of
three major units: the air conditioning unit, watering pipe systems and cool storage
chamber. The water distribution system was designed so that the water is continuously
pumped to the top surfaces of the cooler and to the cooling pad. The top surface of the
structure was designed to enable water to run down all the four lateral surfaces by
gravity, back into a holding tank. The inner dimensions of the unit were 2 X 2 X 1.3 m,
to hold a capacity 0.5 ton vegetables. The frame was constructed from 25 X 25 X 4 mm
angle iron. All the five faces of the cooler were covered by using sheet metal (1 mm in
thickness), welded against each vertical and horizontal angle iron. In order to obtain
good strength the sheet metals were properly welded, both along the vertical and
horizontal angle irons. The water tank was placed below ground level beneath the water
pump (N) and a vertical water pipe was installed to withdraw water from the tank
during operation (D). During operation, water is sprinkled by a small 0.186 KW water
pump (A) over the top surface, to wet the top surface and all four sides of cooling pad
layers by a horizontal perforated pipe (B). The hose was connected from a vertical pipe
to sprinkle water continuously on the cooling pad filled with charcoal (E) from the top
(C). An in-built fan (F) blew air through the cooling pad (E) into the evaporative
cooling chamber, to effectively increase the relative humidity, while the temperature is
decreased. In Fig. 5.1. the directions of arrows show the airflow pattern after passing
176
Chapter 5. Carrot storage (EC)
through the cooling pad. To minimize bruising of perishable produce, and improve
airflow, three equally spaced shelves (H) were inserted.
B
...: ... •••••••• •
c -r--(----~{--f--f-~
M
c
L
H
J K
F
I I I
E D -+--7i : N
I I I
I I I
-I --------_.
A = Water pump (0.5 HP) H = Storage chamber
B = perforated horizontal water pipe I = Ventilation port
C = hose J = Sheet metal
D = Vertical pipe connected to water pump K = Meshed wire holding surface cooling
pad
E= Cooling pad (Charcoal) L = mesh wire
F=Fan M = Wetjutty sack layer
G = Location of thermocouple N = water tank
& hygrometer
Figure 5.1. Schematic diagram of an experimental evaporative cooler for vegetable
storage under hot arid and semi-arid conditions.
177
Chapter 5. Carrot storage (EC)
The dry-bulb air temperature inside the EC was monitored by thermocouples at the
center of the middle shelf (G). An air vent was inserted in the top of the cooler (I). The
three side surfaces and the door were covered with a thin-layer pad of 5-mm jutty sack
(M), which was sandwiched between sheet metal, on the inside (1), and mesh wire (L),
on the outside, facing the ambient air, to allow evaporation (K). In this way the
maximum surface area from which evaporation of water can take place, was exposed.
Reduction in surface temperature would therefore directly be related to the rate of
evaporation.
The can easily be adopted for use by peasants and small-scale farmers from the sub
sector. It can be adapted for use without an electric power source using natural
ventilation for cooling, however, the efficiency of the cooler in reducing temperature
and increasing relative humidity would not be as high as with forced ventilation. The
structure could also be modified to cool vegetables and fruits during local transportation
by truck or long distances by train.
5.2.2. Temperature and relative humidity measurement
The ambient air temperature and relative humidity were measured by usmg a
Jenway-digital psychrometer 5105, UK. The psychrometer recorded dry bulb
temperature, wet bulb temperature, dew point temperature and relative humidity. The
dry bulb air temperature inside the EC was monitored using a thermocouple installed at
the center of the chamber (G), and was connected to a digital temperature control.
Simultaneously, a hygrometer (0 - 50eC) with dry and wet bulb thermometers was used
to monitor the dry and wet bulb temperature of air inside the EC.
5.2.3. Vegetable production
Carrots (var. Nantes) were grown during the summer season of 2001 at the
experimental fields of the Alemaya University, in Eastern Ethiopia. The agro climatic
condition of this location, which is at an altitude range of 1500-2300m, is classified as
178
Chapter 5. Carrot storage (EC)
"Dry Weyna Dega". The climatic conditions of the study site during the carrot
production period from December to May 2001 is shown in Table 5.1.
Table 5.1. The climatic conditions of the study site during sample carrot production (2001).
Month TemQerature (OC) Rain fall Relative Wind Sun shine
Min Max (mm) Humidity (%) intensity
December 3.0 22.3 4.8 39 1.53 9.3
January 5.0 21.8 4.9 39 2.07 9.8
February 6.4 24.4 18.8 38 1.79 10.6
March 12.8 25.0 56.6 51 1.72 6.7
April 11.7 25.4 94.0 41 1.59 8.6
May 13.9 25.2 146.0 55 1.77 8.6
During the growing period, carrots were treated twice with ComCat®. Experimental
plants were treated with 10 g ha-I ComCat® in 350 Iof water (see section 3.2.1), and
control plants 0 g ha-I. Carrots were sprayed once at the three leaves unfolding stage,
and a second time at a vegetative stage. All other agricultural practices were the same as
those normally practiced by the Farm Management Department of the Alemaya
University during carrot production. At a proper maturity stage, carrots were harvested,
topped in the field, and were immediately transported from the farm to the Dire Dawa
University Fruit and Vegetable Research Station, which is 30 km away. The topping,
harvesting and transportation of carrots were made early in the morning before the
temperature was too high. For protection against mechanical injury during
transportation, carrots were packed in plastic crates.
5.2.4. Postharvest treatment
The procedures described in chapter 3, section 3.2.2. were followed. Following
washing, both ComCat® treated and untreated carrots were subjected to one of the
following postharvest treatments according to the procedures:
179
Chapter 5. Carrot storage (EC)
• dipping in chlorinated water (100/-lg. mrl chlorine, made with 5% NaOCI) at
ambient temperature for 20 minutes, packaged in Xtend® Film (see Chapter 3,
section 3.2.2) and stored in EC;
• dipping in chlorine supplemented water, unpackaged and stored in EC
• water washed, packaged in Xtend® Film and stored in EC;
• water washed, unpackaged and stored in EC;
• water washed, packaged in Xtend® Film and stored at ambient conditions, to
serve as a postharvest control; and
• water washed and stored under ambient conditions without packaging, to serve
as a postharvest control.
These treatments were performed in three different containers, each as a replication
for each treatment group. After washing and dipping treatments, the surfaces of carrots
were drip dried to avoid the occurrence of condensation inside the packages. Carrots
were packed in 2 kg packages or unpackaged groups. Randomly, 2 kg samples were
subjected to physiological, microbiological and chemical analyses. Due to limited
facilities, not all analyses could be carried out at the same sampling times. PWL and
percentage marketability were determined on days 0, 4,8, 12, 16,20 and 24. Changes in
moisture content, juice content, pH, TSS, populations of total aerobic bacteria and fungi
were determined on days 0, 8 and 16, and sugars were determined on days 0 and 16.
5.2.5. Physiological weight loss (PWL)
The analysis ofPWL was conducted as described in Chapter 3, section 3.2.4.
5.2.6. Moisture content
The moisture contents of carrots were determined by drying approximately 20 g of
sample at 105°C for 24 hours (Mohammed et al., 1999). Drying was continued until the
change in carrot sample weight became constant (approaching equilibrium moisture
content). The moisture content was calculated per wet material as follows:
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Chapter 5. Carrot storage (EC)
Where
MC = Moisture Content
Ww = weight of wet sample
Wd = weight of dry sample.
5.2.7. Juice content
The carrot juice percentage was obtained according to the methods described by
Waskar et al (1999). The juice content of carrots was extracted using a juice extractor
(Kenwood). The intact carrot weight was recorded prior to juice extraction. After
extraction, the puree was filtered through a double-layer cheesecloth, and the weight of
clear carrot juice was recorded. The juice percentage was expressed as percentage mass
per initial carrot mass used.
. 5.2.8. Chemical analysis
5.2.8.1. pH and total soluble solids (TSS)
The pH of carrots was measured with a TOA pH meter (model HM-20E, Ogawa
Seiki Co., Ltd., Japan). The procedure for TSS determination was as described in
Chapter 3, section 3.2.5.1. The TSS was determined with a bench top 60/70 ABBE (No
A90067, Bellingham & Stanley Ltd, England) refractometer with a reading range ofO to
32 °Brix and Rl range of 1.3 to 1.7 °Brix, with a precision of ± 0.0003. Between
readings, the prism of the referactrometer was cleaned with tissue paper and methanol,
rinsed with distilled water and dried before use. The refractometer was standardized
against distilled water (0% TSS).
5.2.8.2. Sugar analysis
Reducing and total sugars were estimated by using the techniques of Somogyi et al.
(1945). The same procedure was used to estimate reducing and total sugars in carrots
during storage (Phan et al., 1973). Clear juice (10 ml) was added to 15 ml of 80%
181
Chapter 5. Carrot storage (EC)
ethanol, mixed, and heated in a boiling water bath for 30 minutes. After extraction, 1 ml
of saturated Pb(CH3C00)2.3H20 and 1.5 ml ofNa2HP04 were added, and the contents
mixed by gentle shaking. After filtration, the extract was made up to 50 ml with distilled
water. An aliquot of 1 ml extract was diluted to 25 ml with distilled water, of which 0.5
ml was mixed with 1 ml copper reagent (see below) in a test tube and heated for 20
minutes in a boiling water bath. After heating, the contents were cooled under running
tap water without shaking. Arsenomolybdate color reagent (1 ml) (see below) was
added, mixed, made up to 10 ml, and left for about 10 minutes to allow color
development, after which the absorbancy was determined at 540 nm in a Jenway model
6100 spectrophotometer. For total sugar determination, sugar was first hydrolyzed with
IN HCI by heating at 70°C for 30 minutes. After hydrolysis, the determination of total
sugar was made by following the same procedure employed for the reducing sugar
determination. Blanks were prepared using distilled water instead of extract. The
difference between the total and the reducing sugar values correspond to the
nonreducing sugar content of carrots.
Copper reagent was prepared by dissolving 25 g Na2C03, 25 g C4~KNa06.H20, 20
g NaHC03 and 200 g Na2S04 in 800 ml of distilled water, and finally made up to 1000
ml in a volumetric flask.
The arsenomolybdate color reagent was prepared from 25 g (N~)6M07024.4H20, 21
ml of concentrated H2S04 with 3 g NaASS04.7H20, all dissolved in 25 ml distilled
water and kept in an incubator at 37°C for 24 hours before use in the analysis.
5.2.9. Microbiological analysis
5.2.9.1. Total aerobic bacteria and fungi
The microbiological analysis was conducted as described in Chapter 3, section 3.2.6.
Three carrots were cut into pieces with a sterile knife and homogenized using a sterile
mortar and pestle. The procedure used for estimating the microbial populations was the
same as that of Brackett (1990). Samples of 25 g were blended with 225 ml 0.1%
182
Chapter 5. Carrot storage (EC)
peptone water (pH 7.0) in a stomacher bag for 3 minutes. The slurries were serially
diluted in 9 ml 0.1% peptone water. To determine populations of total aerobic
microorganisms, duplicate samples were plated on plate count agar (PCA, Oxoid
CM463, and pH 7.0 ± 0.2) and incubated at 30°C for 2 days. For the determination of
moulds and yeasts, duplicate samples were plated on Rose-Bengal Chlorampehnicol
Agar Base (Oxoid CM549) and incubated at room temperature for 3 to 5 days. In all the
cases pour plate methods were used. The mean 10gIOof viable counts from duplicate
plates were determined.
5.2.10. Subjective quality analysis
The percentage marketable quality of carrots was evaluated according to the
procedures described in chapter 3, section 3.2.7.
5.2.11. Data analysis
The experimental design and data analyses were according to the methods as
described in chapter 3, section 3.2.8.
5.3. Results and Discussion
Due to limited facilities at the Alemaya University, Ethiopia, it was not possible to
carry out the same analyses as reported in Chapter 3. Some different analyses, such as
moisture content and juice content were carried out, as well as alternative analyses such
as reducing sugars. It was also not possible to collect samples or carry out all the
analyses on the same day, as was managed in Chapter 3.
5.3.1. Temperature and relative humidity
The ambient dry bulb environmental air temperature and relative humidity varied
from 25.0°C - 36.0°C and 25.4% - 53.0% during the storage period, respectively. Inside
the evaporative cooler, the dry bulb temperature and relative humidity were between
16.4°C - 22.6°C and 78.0% - 91.0%, respectively. Fig. 5.2. displays mean dry bulb
temperatures (OC) and mean relative humidities (%) at a particular time ranging from 6
183
Chapter 5. Carrot storage (EC)
a.m. up to 6 p.m. of each day against storage time. The differences in dry bulb
temperature between environmental air and the air inside the cooler ranged from 8.6°C-
13.4°C.
During the storage of 24 days, the differences in temperature were found to be at a
minimum (8.6°C) at 6 a.m., whereas the maximum difference (13.4°C) was recorded at
12 am (Fig. 5.3). This was because the rate of evaporation of water from the wet cooling
pad increases with increasing outside temperature. Earlier reports also indicated that
evaporative cooling is more efficient under hot and dry conditions (Seyoum and
W/Tsadik, 2000), as are found in arid or semi-arid regions where the problem of
postharvest losses of vegetables and fruit is severe due to the effect of high temperature
and low relative humidity.
Rama and Narasimham (1991) showed that a temperature drop from 38.0°C to
22.1 °C (a drop of 15.9°C), and heat removal of 2658kJ against a wet bulb temperature
of 21.1 °C was possible. Rama and Narasimham (1991) and Nadre et al (1999) also
reported reductions in temperature of lO-12°C, and relative humidity increases from
23% to 91% during peak summer. However, if the ambient temperature is very high,
this decrease in temperature may not be sufficient to suppress microbial development at
high relative humidity.
From the data presented (Fig. 5.2 and 5.3), it was evident that at 12 am, vegetables
stored under environmental conditions are exposed to harsh conditions, due to a coupled
effect of both high temperature and low relative humidity. The EC was therefore
effective in minimizing these extremes.
184
Chapter 5. Carrot storage (EC)
30 (a) 6 am 100 40 (d) 12 am 100
90 :0:, Xli( XJKlU(lI( 90
80 ~,0 35 80~ 70 >-E 25 70 ;;., ~
" 60 '5 30 60 §9 "9 ..c: ~
ë ... 50 ] ë 50 ~vC- 40 ."~" C"- 25 40 ;;;E 20 .:: E d)v •••• II. ~ , 30 30•• •• •.. • • Ol• 20 i"- 20 • 20 C<:f- : d)C<:
ii' iii 10 10
15 0 15 . 0
0 5 10 15 20 25 0 5 10 15 20 25
Storage time (days)
Storage time (days)
35 . (b) 8 am 100 40 - (e12pm 100
X, JKlI(
.80 80 0~
E·30. >-~ ~
" -60 .~ '-' 30 60 '59
ë 25 .
9 .~
0"- .'... ,.. .......
.~ë
. ·40
.s:
."~ ~ 15. 25 40
E Ol E ."e
" 20 ~_'.. ~ ~•~ ~ d)i- 20 C<: i" ;;;- 20 20 d)C<:
15 . 0 15 - 0
0 5 la 15 20 25 0 5 10 15 20 25
Storage time (days) Storage time (days)
100 100
90
35 80 ~ ~ 35 8070 ~~ '5 t '5
~ 30 60 .~ " 30 60 .~
9 50 s: 9ë ..c: 0:f!.Ol
~ 25 .40 ."::
~
15. 25 40 ."~
C- 30 ;;; E ;;;E v d)
CJ
i- 20 20 C<: i"- 20 20 C<:
IS 10_L_ ~ 0 15 -0
o 10 15 20 25 0 10 15 20 255
Storage time (days) Storage time (days)
100
90
80
70
60
50
40
30
20
10
15 o
o la 15 20 25
Storage time (days)
___ T db-ambient . - -•... 'ldb-cooler
____._.. RH-ambient - - .)1:- - - RH-cooler
Figure 5.2. Temperature (OC) and relative humidity (%) of the environmental air and the
air inside the EC during carrot storage at 6 am (a), 8 am (b), lOam (c), 12 am (d), 2 pm
(e), 4 pm (f) and 6 pm (g).
185
Chapter 5. Carrot storage (EC)
40 (a) I
,.-... 35 o Tdb-ambient 0 Tdb-cooler r--
U -r-- -
'-' 30 r-- Iil) r--
!3 25 r-- I~ - I
I-<
il) 20 - f-- -
r-- if-- I
E" - '--
..i.l..). 15 -
§ I
il)
:;B 10
-
5 -
0 I
Daytime
Figure 5.3. (a). The effect of daytime on the average environmental and evaporative
cooler temperatures (OC) during storage of carrots.
100 (b) ~
90 o RH-ambient 0 RH-cooler
,.-... 80 ,...-- .....- ,...--
.---- .--- r-- ..--
~
'.._/
.e 70 -
:-Q 60 -
j 50 - .---
40 .---il) .---
.~ r--...... - .---
..Z! 30 - r--
~ 20 -
10
0
Figure 5.3. (b). The effect of daytime on the average environmental and evaporative cooler
relative humidity (%) during storage of carrots.
186
Chapter 5. Carrot storage (EC)
5.3.2. Physiological weight loss, moisture and juice content
Dipping carrots in chlorine supplemented water seemed to have an effect on the
PWL during storage (Table 5.2), although only significant at P S 0.09. The PWL was
higher in carrots dipped in chlorinated water, compared to those dipped in tap water.
Table 5.2. Changes in physiological weight loss of carrots stored in evaporative cooling
chamber and ambient temperature (RT) for 24 days.
Physiological loss in weight (%)
Treatment Day4 Day 8 Day 12 Day 16 Day20 Day24
b
Cornf'at", Ch, MAP, EC 0.568d 4.970 ef 10.291 d 12.807 d 17.100 b 20.649
e
Control, Ch, MAP, EC 0.877 d 6.752 e 12.056 d 15.093 19.485 b 23.108 b
Comf'at", Ch, EC 1.286 cd 10.718 ede 20.361 be 25.947 b 36.272 a 45.084 a
Control, Ch, EC 6.667 bed 13.867 cd 24.603 be 30.545 b 41.626 a 50.107 a
Cornf'at'", H20, MAP, EC 0.688 d 5.097
e 7.907 e 10.645 de 14.841 e 18.625 e
be
Control, H 0, MAP, EC 0.700 d 5.363 e 8.628 e 11.429 d 15.858 20.246 be2
ComCat®, Ch, MAP, RT 8.724 abc 16.137 be 22.275 be 26.323 b 33.553 a 40.600
a
. Control, Ch, MAP, RT 12.096 ab 20.298 b 26.867 b 31.580 b 38.016 a 44.598 a
Comt.at", H20, EC 0.506 d 9.246 de 16.595 cd 22.598 be 34.424 a 43.479 a
Control, H 0, EC 2.043 ed 10.621 de 20.653 be 26.768 b 33.968 a 41.986 a2
Comf'at", H20, RT 9.993 ab 47.452 a 70.810 a 88.604 a
Control, H20, RT 14.034 a 44.656 a 70.254 a 84.399 a
Significance
Preharvest treatment (A) NS
Disinfecting treatment (B) *
Packaging + Storage temperature (C) ***
AXB NS
AXC NS
BXC ***
AXBXC *
NS, *, *** Nonsignificant or significant at P :=; 0.09 or 0.001 respectively. Means within a column followed by
the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The
coefficient of variation and standard error were 0.150 and 1.196 respectively. LSD Value = 6.508.
187
Chapter 5. Carrot storage (EC)
The combined effect of MAP and storage temperature was found to be highly
significant (P :s 0.001) in reducing the PWL during storage. The loss in PWL was
higher from unpackaged than packaged carrots stored in the EC.
The results in Table 5.2 show the importance of MAP for use in combination with
EC to maintain freshness and increase shelf life. The PWL from unpackaged carrots
stored at ambient temperature was above 85% at the end of 16 days of storage
respectively, whereas for carrots packaged and stored at ambient temperature, the PWL
was found to be below 32% during the same storage time. While the unpackaged carrots
were dried out after 16 days, the packaged ones lasted up to 24 days storage, with a
PWL of 40 - 45%. The effect of EC on the PWL was also significant (P :s 0.05) during
the storage period. Due to the lower temperature and higher relative humidity, the PWL
was significantly reduced (P :s 0.05), which was in agreement with previous studies by
Royand Pal (1994) and Waskar ef al (1999). The PWL in packaged carrots stored in EC
was only 18-23%, while unpackaged carrots stored in EC showed a PWL of 41-50%.
Disinfecting with chlorinated water had no significant effect on PWL. The PWL was
higher in control carrots, however not significant (P > 0.05), perhaps because the sizes
of the control carrots were smaller than the ComCat® treated ones. Similar results were
observed in Chapter 3, Table 3.1. In addition to the effect of size on the PWL, plant
growth hormones (gibberilin and auxin) play an important role in reducing the PWL
during storage (Salunkhe ef al, 1991; Rodrigues and Subramanyam, 1996). These
hormones are the major constituent of ComCat® and hence could have contributed to
the reduction in PWL during storage of carrots. Compared to the storage at room
temperature in Chapter 3, which was at the same temperature as ion EC, but with a
lower relative humidity, the PWL was less. The higher humidity therefore prevented
moisture loss through evaporation.
188
Chapter 5. Carrot storage (EC)
Table 5.3. Changes in moisture content of carrots stored in evaporative cooling chamber and
ambient temperature (RT) for 24 days.
Moisture content (% w.b.)
Treatment DayO Day8 Day 16 Day24
ComCat®, Cb, MAP, EC 88.205 a 88.079 a 87.711 a 86.819 a
Control, ei,MAP, EC 88.002 a 87.828 a 87.060ab 85.806 ab
ComCat®, Ch, EC 88.205 a 87.335 ab 86.096 ab 84.312 ab
Control, C12,EC 88.002 a 87.703 a 86.656 ab 83.771 be
CorrrCar'", H20, MAP, EC 88.205 a 87.362 a 87.174 ab 85.685 ab
Control, H20, MAP, EC 88.002 a 87.508 ab 86.533 a 84.763 ab
ComCat®, Ch, MAP, RT 88.205 a 87.585 a 85.408 b 84.296 b
Control, Ch, MAP, RT 88.002 a 85.469 be 84.953 be 83.681 e
CorrrCat'", H20, EC 88.205 a 85.878 be 84.917 abe 82.989 e
d
Control, H20, EC 88.002 a 85.278 be 83.007 ed 81.747
ComCat®, H20, RT 88.205 a 79.117
d 72.700 e
Control, H20, RT 88.002 a 83.936 b 75.144 e
Significance
Preharvest treatment (A) NS
Disinfecting treatment (B) *
Packaging + Storage temperature (C) ***
AXB NS
AXC NS
BXC ***
AXBXC *
NS, *, *** Nonsignificant or significant at P ~ 0.07 or 0.001 respectively. Means within a column followed
by the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The
coefficient of variation and standard error were 0.027 and 0.303 respectively. LSD Value = 3.643.
Table 5.3 shows moisture loss of carrots during EC storage. General trends of higher
moisture content in packaged ComCat® treated carrots dipped in chlorinated water and
stored in EC were noticed, however not significant (P > 0.05). The conservation or loss
of moisture was due to MAP and storage at EC temperature, or the lack thereof,
respectively. The moisture content of carrots was therefore significantly affected with
189
Chapter 5. Carrot storage (EC)
packaging and storage temperature (P :s 0.001). Chlorine disinfecting did not affect (P >
0.05) moisture loss, although the loss was significant at P :s 0.07. Since these results
basically are the same as that of PWL (Table 5.1), it can be concluded that the PWL
observed, is mainly due to the loss of moisture, and not due to metabolic activity in the
form of C02.
Table 5.4. Changes in juice content of carrots stored III evaporative cooling
chamber and ambient temperature (RT) for 24 days.
Juice Content (%)
Treatment DayO Day8 Day 16 Day24
Comf'at'", Ch, MAP, EC 64.467 a 62.193 a 60.194 a 59.062 a
Control, ei;MAP, EC 60.421 ab 60.051 ab 58.625 ab 57.793 ab
Comf'at'", ei, EC 64.467 a 54.4l3 bed 53.870 be 51.208 b
Control, ei; EC 60.421 ab 55.383 bed 53.428 abc 52.547 b
Cornf'at", H20, MAP, EC 64.467 a 60.509ab 57.051 abc 57.030 ab
Control, H20, MAP, EC 60.421 ab 58.208 abe 56.125 abe 55.156 ab
ComCat®, Ch, MAP, RT 64.467 a 59.604 be 52.516 e 51.058 b
Control, Ch, MAP, RT 60.421 ab 53.786ede 49.346 e 46.698 ed
ComCat®, H20, EC 64.467 a 56.827 bed 54.879 be 52.728 b
Control, H20, EC 60.421 ab 54.247 bed 51.047 be 48.575 bed
ComCat®, H20, RT 64.467 a 39.107
e 27.472d
Control, H20, RT 60.421 ab 46.596 de 29.610
d
Significance
Preharvest treatment (A) NS
Disinfecting treatment (B) *
Packaging + Storage temperature (C) ***
AXB NS
AXC NS
BXC **
AXBXC *
NS, *, **, *** Nonsignificant or significant at P::; 0.09 0.01 or 0.001 respectively. Means within a
column followed by the same letter(s) are not significantly different according to Duncan's
multiple range test (P < 0.05). The coefficient of variation and standard error were 0.103 and
1.0 I0 respectively. LSD Value = 9.089.
190
Chapter 5. Carrot storage (EC)
The juice content (Table 5.4) explains nothing more than PWL and moisture loss.
However, this analysis was included, mainly to investigate differences between
ComCat® treated and control carrots, as a measurement of water binding, due to
possible differences in structural components such as cellulose and other fibers. There
are thus no differences of that kind.
5.3.3. Chemical changes
5.3.3.1. Total soluble solids (TSS)
The results presented in Table 5.5 showed that there was a general trend of an
increase in TSS of carrots during storage from around 8.3 to maximum 13.67 °Brix at
EC after 24 days, and as high as 18 °Brix for carrots stored unpackaged at ambient
temperature after 16 days. The changes in TSS also fall within the same limits as that
observed in Chapter 3. Lingaiah and Huddar (1991), Waskar et al. (1999) and Jitender-
Kumar et al. (1999) also showed an increasing trend of TSS in carrots, but at lower
numbers, i.e. from 1.9-2.9 °Brix, for packaged carrots stored in EC.
At harvest the TSS content of ComCat® treated carrots was slightly lower than that
of the control, and remained that way during storage, however, these differences were
not significant (P > 0.05), although the two-way interaction between preharvest and
prepackaging treatments was significant at P :'S0.09 on the changes in TSS of carrots.
The effect of disinfecting carrots in chlorinated water was found to be not significant ((P
> 0.05) on the changes ofTSS of carrots during storage.
The combined effect of packaging and storage at environmental conditions were
highly significant (P:'S 0.001) on the TSS content of carrots. The result also showed that
there is an overall interaction (P :'S0.001) between prepackaging disinfecting of carrots,
MAP and EC temperatures during storage. In general, the TSS of carrots was better
maintained in the packaged carrots stored inside the EC. The TSS of carrots was
affected by the interaction between the pre- and postharvest treatments during storage,
however, only at a significance level of P :'S0.09. These result thus indicate that the
191
Chapter 5. Carrot storage (EC)
quality of carrots may be maintained better by applying the combinations of pre- and
postharvest treatments such as ComCat® treatment, disinfecting, MAP and followed by
EC during storage.
Table 5.5. Changes in TSS of carrots stored in evaporative cooling chamber and
ambient temperature (RT) for 24 days.
Total soluble solid (OBrix)
Treatment DayO Day8 Day 16 Day24
c
ComCat®, ei;MAP, EC 8.30 ab 10.77 ed 9.97 10.20 d
Control, Ch, MAP, EC 8.60a 10.77 cd 10.20 e 11.40 cd
Comf.at'", C12,EC 8.30 ab 10.53 ed 11.30 be 11.38 ed
Control, ei, EC 8.60a 11.43 be 10.87 be 13.67 a
ComCat®, H20, MAP, EC 8.30 ab 10.48 ed 9.96
e 10.67 d
Control, H20, MAP, EC 8.60
a 10.55 cd 9.25 c 11.50 bed
Comf'at", bcCh, MAP, RT 8.30 ab 10.50 cd 11.17 12.73 abc
Control, Ch, MAP, RT 8.60a 10.33 cd 10.97 be 12.87 ab
ComCat'", H20, EC 8.30 ab 9.78 d 12.70 b 12.70 abc
Control, H20, EC 8.60
a 10.75 cd 11.23 be 13.10 a
ComCat®, H20, RT 8.30 ab 14.87 a 18.15
a
Control, H20, RT 8.60a 14.62 a 17.00 a
Significance
Preharvest treatment (A) *
Disinfecting treatment (B) NS
Packaging + Storage temperature (C) ***
AXB *
AXC NS
BXC ***
AXBXC *
NS, *, *** Nonsignificant or significant at P ~ 0.09 or 0.001 respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range
test (P < 0.05). The coefficient of variation and standard error were 0.077 and 0.084 respectively.
LSD Value = 1.397.
192
Chapter 5. Carrot storage (EC)
5.3.3.2. pH
The initial pH values of ComCat® and control carrots were 6.01 and 5.98
respectively, but the difference was not significant (Table 5.6). The pH of ComCat®
treated carrots were maintained around 6.00 during the 24 days of storage in the EC.
The pH of ComCat® treated carrots significantly (P :s 0.05) differed from the pH of
control carrots after 8 days of storage at room temperature.
Table 5.6. Changes in pH of carrots stored in evaporative cooling chamber and ambient
temperature (RT) for 24 days.
H
Treatment DayO Day8 Day 16 Day 24
Comf'at", ch, MAP, EC 6.01 a 6.08 be 6.08 ab 6.06a
Control, ei; MAP, EC 5.98 ab 6.02 ede 6.02 be 6.06a
Cornf'ar", Ch, EC 6.01 a 6.26a 6.12 a 6.08a
Control, Ch, EC 5.98 ab 6.04 bed 6.06 be 5.99 be
. ComCat®, H20, MAP, EC 6.01 a 6.08 be 6.01 be 5.98 abc
Control, H20, MAP, EC 5.98 ab 5.95 de 5.99 cd 6.03 a
Comï.at", ei, MAP, RT 6.01 a 5.93 de 6.00 be 5.87 be
Control, Ch, MAP, RT 5.98 ab 5.91 c 5.91 de 5.64 d
CorrrCat", H20, EC 6.01 a 6.11 b 6.02 be 6.00 ab
Control, H20, EC 5.98 ab 5.98 ede 6.01 be 6.03 a
CorrrCat'", H20, RT 6.01 a 6.12 b 5.84 e 5.84 c
Control, H20, RT 5.98 ab 5.98 ede 5.97 ed 5.97 abc
Significance
Preharvest treatment (A) **
Disinfecting treatment (B) NS
Packaging + Storage temperature (C) ***
AXB *
AXC *
BXC ***
AXBXC **
NS, *, **, *** Nonsignificant or significant at P $ 0.09, 0.05 or 0.001 respectively. Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple
range test (P < 0.05). The coefficient of variation and standard error were 0.010 and 0.004 respectively.
LSD Value = 0.103.
193
Chapter 5. Carrot storage (EG)
The changes in pH of the packaged ComCat® treated carrots dipped in chlorinated
water showed significant (P :S 0.05) differences from that of the packaged control
carrots treated with chlorine during storage at ambient temperature, although there was
no significant difference in those stored in EC. MAP had a slight effect on the pH of
carrots. As a general trend the rate at which the pH was increasing in packaged
ComCat® treated carrots was lower compared to unpackaged ones. Similarly, general
trends of rapid increase in pH of control carrots were noticed during storage. The
storage temperature also affected the pH significantly (P :S 0.05) during storage. As a
general trend, a drop in pH of carrots was observed during storage at ambient
temperature, which could be associated with higher rates of respiration, since acids are
formed due to the catabolism of carbohydrates (Hao et al., 1999). However, the results
of Hao et al. (1999) do not agree that packaging material and storage temperature
significantly affected the pH of carrot (P S 0.05).
Chlorine treatment had no significant effect on the pH of stored carrots, but the two-
way interaction between postharvest treatment i.e. disinfecting treatment, MAP and
storage temperature was highly significant. The combined effect of preharvest and
disinfecting treatment was significant, but only at P :S 0.09. There was also a significant
two-way interaction between preharvest and MAP + storage temperature during storage
at P :S 0.09 level. The three-way interaction between ComCat® treatment, disinfecting
treatment, MAP and storage temperature was found to be significant at P :S 0.05 level.
5.3.3.3. Sugar analysis
The sugar dynamics during storage are shown in Table 5.7. The non-reducing and
total sugars of carrots decreased consistently during the 16 days of storage, while the
reducing sugar contents seemed to increase in some carrot samples subjected to
different treatments during 16 days, confirming the findings of Phan et al. (1973) and
Nilsson (1987). In Chapter 3 an increase in glucose content during storage was also
noted, which also support these results obtained during EC storage.
194
Chapter 5. Carrot storage (EC)
Table 5.7. Changes in reducing, non-reducing and total sugar contents of carrots stored in
evaporative cooling chamber and ambient temperature (RT) for 24 days.
Treatment Total Reducing sugar Non-reducing Sugar
Sugar (g/1OOg) (g/100g) (g/100g)
DayO Day 16 DayO Day 16 DayO Day 16
ab
ComCat®, Ch, MAP, EC 6.910a 7.187 a 2.670
a 4.784 a 4.240 2.978 be
Control, Ch, MAP, EC 7.412 a 6.917 a 2.694 a 2.763 b 4.981 a 4.154 ab
ComCat®, Ch, EC 6.910a 4.934 b 2.670
a 2.245 bc 4.240ab 2.689c
Control, Ch, EC 7.412 a 5.315 b 2.694 a 0.971 d 4.981 a 4.344 a
ConrCat'", H20, MAP, EC 6.910 a 5.127 b 2.670
a 2.586 be 4.240 ab 2.541 c
Control, H20, MAP, EC 7.412
a 3.782 c 2.694 a 1.948c 4.981 a 1.835 cd
6.910 a 3.906 c 2.670aCom'Cat'", H 0, EC 2.969 b 4.240 ab 0.936 d2
Control, H20, RT 7.412 a 1.924 d 2.694 a 0.979 d 4.981 a 0.945d~
Significance Total Reducing Non-reducing
sugar sugar sugar
Preharvest treatment (A) NS * NS
Disinfecting treatment (B) *** ** ***
Packaging + storage temperature (C) **** **** *
AXB * NS *
AXC NS NS NS
BXC * ** NS
AXBXC ** * NS
NS, *, **, ***, **** Nonsignificant or significant at P::; 0.09,0.05,0.01 or 0.001 respectively. Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple range test
(P < 0.05). The coefficient of variation and standard error were 0.195 and 0.180 for reducing sugar, 0.192 and
0.306 for nonreducing sugar and 0.086 and 0.217 for total sugar respectively. LSD Value = 0.836,1.158 and
0.872 for reducing, nonreducing and total sugar respectively.
In Chapter 3 it was shown that ComCafID treatment significantly affected the changes
in glucose and fructose content, while the total sugar content was not affected. Here
ComCat® treatment significantly affected the changes in reducing sugars at p ~ 0.09),
which would therefore repeat the results observed for glucose content in Chapter 3. It
shows that ComCat® in general has an effect on sugars. At harvest, there was no
significant difference (P > 0.05) in total and non-reducing sugar content between
ComCat® treated and untreated control carrots, however at p ~ 0.09, ComCat® treated
195
Chapter 5. Carrot storage (EC)
carrots had a lower reducing sugar content compared to the controls. Similarly, the
ComCat® treated carrots had a lower glucose content at harvest in the carrots
investigated in chapter 3. The results in Chapter 3 showed that even though the free
sugars were higher in controls, the total available carbohydrates (TAC) were found to be
higher in ComCat® treated carrots, than in the control carrots. It should be mentioned
that a concentration effect could play a role in the results of the current Chapter, as it
was noted that ComCat® treated carrots contain slightly more juice than the control
carrots (Table 5.4). After 16 days of storage, the highest total sugar content was
maintained in disinfected and packaged carrots stored in EC. This result shows that the
postharvest treatments such as disinfecting, MAP and EC, can maintain the chemical
quality, regarding the sugars, better during short storage periods.
A considerable decrease in total sugar content was found in carrots stored at ambient
temperature compared to EC. There was a 74% percent depletion in total sugar content
in unpackaged carrots stored at ambient conditions. The reason for this could be
associated with a high respiration rate of carrots stored at relatively higher temperature.
High temperature increases the metabolic activity, and therefore also the activity of
enzymes, responsible for biochemical reactions, in carrots during storage. Faster
utilization of freely available sugars by microorganisms could also contribute to the
reduction of sugars.
The interaction between disinfecting, MAP and storage temperature had a significant
(P :::;0.05) effect on the changes in reducing sugar in carrots during 16 days at EC
temperature. The reducing sugars were significantly higher in both ComCat® treated
carrots and controls that were disinfected in chlorinated water, packaged and stored in
EC. The two-way interaction between the preharvest ComCat® treatment and
disinfecting had a significant (P :::;0.05) influence on the changes of non-reducing sugar
content. The three-way interaction between the pre- and postharvest treatment on the
changes of reducing sugar content of carrots was significant (P :::;0.09) during storage.
196
Chapter 5. Carrot storage (EC)
These results thus demonstrated that ComCat® treatment in general has an effect on the
sugar content.
5.3.4. Microbiological changes
5.3.4.1. Total aerobic bacteria
Table 5.8 displays the estimated populations of total aerobic bacteria in stored
carrots. The populations oftotal aerobic bacteria on carrots were significantly (P ::s; 0.01)
affected by disinfecting in chlorinated water, which significantly reduced microbial
populations for up to 16 days.
MAP had a significant effect (P ::s; 0.01) on the population of the total aerobic
bacteria. The populations of total aerobic bacteria was lower in packaged carrots at the
end of 16 days in the EC compared to those in unpackaged carrots.
Table 5.8 shows that the estimated population of total aerobic bacteria was higher in
carrots stored at ambient conditions, than in carrots stored in the EC for 8 days. A sharp
increase in the populations of aerobic bacteria in carrots stored at ambient temperature
during the first few days were observed, followed by a slight drop thereafter. The reason
for this was due to the availability of free moisture in carrots during the first few days,
after which they tended to dry out, leaving less moisture for microbial development.
The lower sugar contents in these carrots (Table 5.3, 5.4 and 5.7) could also contribute
to this observation.
The preharvest ComCat® treatment had an effect on the estimated populations of
total aerobic bacteria at p ::s; 0.09. Similar results were also found in the experiment in
Chapter 3. The preharvest ComCat® treatment was shown to have a significant effect on
the pH of carrots during storage, which could be the reason for the effect of the
preharvest treatment on microbial growth and their population during storage. The
populations of aerobic bacteria also remained lower throughout storage, but only at a
significance level of P :s 0.08. The two- and three-way interactions between the
197
Chapter 5. Carrot storage (EC)
preharvest treatment and postharvest treatments were not significant for the total aerobic
microorganisms in carrots stored in EC.
Table 5.8. Populations of total aerobic bacteria in carrots packaged or
unpackaged and stored in evaporative cooling chamber or at ambient
temperature (RT) for 16 days.
Total aerobic bacteria (Log CFU/g)
Treatment DayO Day8 Day 16
ComCat®, Ch, MAP, EC 4.845 ab 4.823 d 4.712 e
ComCat®, Ch, EC 4.845 ab 5.125 cd 5.273 be
CornCat", H20, MAP, EC 4.845 ab 5.996 abc 5.823 b
Comf'at", H20, EC 4.845 ab 6.378 ab 7.022 a
Control, er, MAP, EC 5.463 a 5.120 ed 5.038 c
Control, ei; EC 5.463 a 5.697 bed 5.822 b
Control, H20, MAP, EC 5.463 a 6.230 abc 6.664 a
a a
Control, H20, RT 5.463 a 7.174 6.500
Significance
Preharvest treatment (A) *
Disinfecting treatment (B) **
Packaging + storage temperature (C) **
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P ::; 0.05, 0.01 or 0.001 respectively.
Means within a column followed by the same letter(s) are not significantly different
according to Duncan's multiple range test (P < 0.05). The coefficient of variation and
standard error were 0.093 and 0.268 respectively. LSD Value = 0.854.
5.3.4.2. Total moulds and yeasts
The populations of moulds and yeasts remained lower throughout the storage period
of 16 days in ComCat® treated, packaged carrots dipped in chlorinated water, and stored
in EC (P :::;0.05) (Table 5.9). Disinfecting carrots in chlorinated water also highly
198
Chapter 5. Carrot storage (EC)
affected (P ::; 0.001) the populations of moulds and yeasts during 16 days of storage.
This indicated that the use of EC combined with disinfecting treatments significantly
reduced decay during storage.
Two-way interactions were observed between packaging + storage temperature and
both preharvest treatment (P :s 0.05) and disinfecting treatment (P :s 0.001). With EC,
the minimum temperature attained was only 16°C, which could mean that disinfecting
carrots in chlorinated water would have little effect in reducing and limiting the growth
of aerobic bacteria during storage, compared to storage at 1°C shown in chapter 3. The
other possible reason for the presence of higher microbial populations after disinfecting
with chlorine, could be associated with the effect of the chlorine solution on the surface
tissue of carrots (Seyoum et al., 2003), which could make conditions favorable for
microorganisms to grow again. Work of other researchers on the EC of fruits and
vegetables focused more on the physiological and chemical changes during evaporative
cooling storage, without emphasis on the hazard of postharvest microbiological aspects
. (Royand Pal, 1993; Pal and Roy, 1988; Waskar et al., 1999).
The relative humidity in this study was also high, aiding to the proliferation of
microorganisms associated with fruits and vegetables. Compared to the storage at room
temperature in Chapter 3, which was the same as in the EC, however, with a lower
relative humidity, the counts of total bacteria, as well as moulds and yeasts, are in the
same order. However, in both cases of storage at higher temperatures, the microbial
populations were not as low as observed during storage at 1°C. In general, the
preharvest ComCat® treatment had a slight effect on the improvement of the
microbiological quality of carrots in terms of less total aerobic bacteria, and mould and
yeast populations during storage.
The result demonstrated the importance of combining effective disinfecting
treatments with packaging and EC of carrots, particularly under hot and arid conditions.
The combined effect of pre- and postharvest treatments, including EC, could aid to
199
Chapter 5. Carrot storage (EC)
solve the problems identified by several workers in Ethiopia (Wolde, 1991; Storck et
al., 1991, Kebede, 1991; Agonifar, 1991).
Table 5.9. Populations of moulds and yeasts In carrots packaged or
unpackaged and stored in evaporative cooling chamber or at ambient
temperature (RT) for 16 days.
Moulds and yeasts
Treatment DayO Day8 Day 16
® .
ComCat , Ch, MAP, EC 4.521 ab 3.856 d 3.693 d
ComCat®, ch, EC 4.521 ab 4.682 c 4.248 d
ComCat", H20, MAP, EC 4.521 ab 5.534 b 5.460 be
CorrrCat", H20, EC 4.521 ab 5.686 b. 5.655 be
Control, Ch, MAP, EC 4.841 a 4.055 d 3.705 d
Control, Ch, EC 4.841 a 5.525 b 5.121 c
Control, H20, MAP, EC 4.841 a 5.824 ab 6.026 ab
Control, H20, RT 4.841 a 6.308 a 6.268 a
Significance
Preharvest treatment (A) *
Disinfecting treatment (B) ***
Packaging + storage temperature (C) ***
AXB NS
AXC *
BXC ***
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P :5 0.05, 0.0 I or 0.001 respectively. Means
within a column followed by the same letter(s) are not significantly different according to
Duncan's multiple range test (P < 0.05). The coefficient of variation and standard error
were 0.063 and 0.082 respectively. LSD Value = 0.514.
5.3.5. Subjective quality analysis
MAP, storage in EC, as well as disinfecting treatment of carrots in chlorinated water,
had significant (P ~ 0.05) effects on the percentage marketability of carrots (Table
5.10). These results indicated that preharvest disinfecting treatments must be coupled
200
Chapter 5. Carrot storage (EC)
with EC in order to decrease postharvest decay, insure a relatively longer shelf life of
vegetables, and maintain a better quality. It seemed as if the marketability of ComCat®
treated carrots was, in general, somewhat better than the controls, however, not
significantly (P ::s; 0.05). Marketability was not determined over storage time in Chapter
3, because the deterioration was not as fast. The marketability can therefore not be
compared.
Table 5.10. Percentage marketable carrots of different treatments after 4,8, 12, 16,20 and 24
days of storage at evaporative cooling and ambient temperatures (RT) for 24 days.
Marketable carrots (%)
Treatment DayO Day4 Day8 Day 12 Day 16 Day20 Day24
CorrrCat", ch, MAP, EC ico- 100a 100 a 100a 100a IOOa 98.3 a
Control, Ch, MAP, EC JOOa 100a lOOa 100a IOO
a 96.7 ab 95 ab
CorrrCat'", Ch, EC JOOa IOOa 100a 96.7 ab 96.7 ab 86.7 def 85 de
Control, ei; EC 100 a JOOa 100a 96.7 ab 93.3 abed 93.3 abed 91.7 abed
CorrrCat", H20, MAP, EC 100a JOOa 93.3 abed 93.3 abed 93.3 abed 93.3 abed 93.3 abe
Control, H20, MAP, EC 100a 100 a 100 a 100 a 91.7 abede86.7 def 83.3 e
h
ComCat'", er, MAP, RT 100 a 83.3 e 71.7e 55 f 43.3 g 26.7 15g
h
Control, ei,MAP, RT lOOa 90 be 73.3 e 56.7f 43.3 g 26.7 8.3 g
e
ComCat®, H20, EC lOOa 100 a 98.3 ab 88.3 ede 85 ef 81.7 f 81.7
Control, H20, EC 100a IOO
a 96.7 ab 86.7 de 83.3 ef 78.3 fg 78.3 ef
CorrsCat'", H 0, RT lOOa 41.7d2 -
Control, H20, RT 100a 40d
Significance
Preharvest treatment (A) NS
Disinfecting treatment CB) *
Packaging + Storage temperature CC) ***
AXB NS
AXC NS
BXC **
AXBXC NS
NS, *, **, *** Nonsignificant or significant at P ~ 0.05, 0.0 I or 0.00 I respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test (P <
0.05). The coefficient of variation and standard error were 0.052 and 0.826 resEectivel~. LSD Value = 6.826.
201
Chapter 5. Carrot storage (EC)
The combination of postharvest treatments including MAP and storage conditions,
highly affected the marketability of carrots during the 24 days of storage, which was
significant at p ~ 0.0011eveL The percentage marketability of unpack aged carrots stored
at ambient conditions dropped to 40% during the first 4 days of storage due to excessive
dehydration and visible mould growth. Hardening of texture and visible mould growth
were the problems in the case of packaged carrots stored at ambient conditions. No
sprouting of packaged carrots stored at ambient conditions was observed due to the high
temperature that caused excessive dehydration. In the EC, no sprouting was observed,
which is one of the major postharvest problems of carrots during storage at relatively
higher temperature (Berg and Lentz, 1966).
5.4. Conclusions
A forced ventilation EC unit was developed, using locally available construction
material in Dire Dawa, Ethiopia. The unit was designed for possible use on farms,
wholesalers, retailers and exporters to close by export markets. It can be fitted to any
storeroom, and construction can be modified, within limits, according to desired
capacities. This unit reduced the temperature by 8.4 - 13.4°C below ambient
temperature, with a rise of relative humidity to 78 - 91% during storage. The
temperature and relative humidity were maintained within constant limits, although the
outside ambient temperature and relative humidity varied. The shelf life of carrots kept
in the unit was dramatically increased from 4 days to 24 days by 6 fold, compared to
storage at ambient conditions, mainly by preventing loss of moisture.
The quality of ComCat® treated carrots stored in the EC remained as good as the
quality of the untreated control carrots. The PWL, and loss in moisture and juice of
carrots were slightly higher in untreated control carrots than in ComCat® treated carrots,
although the differences were not significant (P > 0.05). The population of moulds and
yeasts, pH value and total sugar content of carrots were affected significantly (P ~ 0.05)
by the preharvest ComCat® treatment during 16 days of storage in EC. The ComCat®
treated carrots had a lower total sugars content at harvest, however, the effect of
202
Chapter 5. Carrot storage (EC)
ComCat® treatment on reducing and non-reducing sugar was not significant (P > 0.05)
at harvest as well as during the storage period of 16 days.
Unfortunately, not all the analyses for quality could be carried out as in Chapter 3.
Only PWL, TSS and the microbiological analysis could be carried out. The reducing
sugar content, determined in this chapter, can be compared with the glucose content in
chapter 3. Regarding the comparison between ComCat® treated and controls, both
investigations show similar insignificant results for changes in TSS and total sugar
content, significant differences in reducing sugar or glucose content, but different
changes in PWL. It could therefore be concluded that ComCat® treated carrots also
express better quality attributes during EC storage than the untreated controls.
Disinfecting carrots in chlorinated water slightly affected nonreducing and reducing
sugar content, population of total aerobic bacteria, moulds and yeasts, and marketability
during the storage of carrots in EC. In general, the results demonstrated that disinfecting
treatment is an important postharvest handling step to be coupled with EC to maintain
microbiological quality of carrots.
MAP + storage temperature improved all quality aspects tested. The physiology,
biochemistry and microbiology of the root part of plants differ from the other
physiological parts, such as fruit. The data obtained on the storability characteristics of
ComCat® treated, (and control carrots) may not be appropriate to predict the storability
of fruit by EC. Based on this view, and information obtained in Chapter 4, the study on
the storability of ComCat® treated (and control tomatoes) in forced ventilation EC was
investigated and presented in the next chapter.
203
CHAPTER6
EFFECT of PREHARVEST TREATMENT and
FORCED VENTILATION EVAPORA TIVE
COOLING on TOMATOES
Abstract
An evaporative cooler (EC) unit, which allowed an average drop of 11.5°C in
temperature and a rise of 43.93% in relative humidity relative to environmental
conditions, was used to store tomatoes. The quality of tomatoes stored in this cooler was
maintained better, compared to tomatoes stored at ambient conditions, with more than
70% shelf life extension. Preharvest ComCat® treated tomatoes contained lower TSS,
reducing sugars and total sugars at harvest, and showed better keeping quality in terms
of PWL, juice content, TSS and sugars, compared to untreated controls. No distinct
effect of ComCat® treatment on microbial populations was found. Disinfecting with
chlorinated water controlled total aerobic bacteria, moulds and yeasts during storage in
the EC. MAP and EC temperatures helped to control weight loss, improve juice content,
total aerobic bacteria, moulds and yeasts, and resulted in lower pH of stored tomatoes.
Microperforated MAP film prevented condensation inside packages and resulted in
better marketability when combined with EC. The benefits from the combined effect of
pre- and postharvest treatment on tomatoes include: reduction of PWL and loss of fruit
juice, better keeping quality in terms of TSS, pH, non-reducing sugar content, total
sugar content, microbiological quality, and marketability.
6.1. Introduction
The problems experienced with postharvest vegetable handling in developing
countries such as Ethiopia have been reviewed in Chapter 2 section 2.5.3. and were
again mentioned in Chapter 5 section 5.1. It was mentioned that ComCat® treatment of
vegetables could increase yield, and the postharvest performance of ComCat® treated
tomatoes was investigated in Chapter 4. It was found that these tomatoes performed
204
Chapter 6. Tomato storage (EC)
better than untreated controls, not just at the recommended optimum storage
temperature of l3°C, but also at higher temperatures. From those results, it was
suggested that the postharvest performance of ComCat® treated tomatoes be carried out
at a controlled temperature that is higher than the recommended optimum storage
temperature, and using storage facilities which are suited for use in developing
countries. The aim of the work in this Chapter is, therefore, to investigate the
postharvest quality of ComCat® treated tomatoes in a low-cost EC at temperatures
between 16°C and 24°C and relative humidity of 73-92%.
The objectives of the study are:
1. to investigate the effectiveness of forced ventilation EC in reducing temperature and
increasing relative humidity during storage of tomatoes;
2. to investigate the storability of preharvest ComCat® treated tomatoes using EC
methods;
3. to explore the synergistic effect of pre-packaging treatments (chlorine supplemented
water) when combined with modified atmosphere packaging and EC storage.
6.2. Materials and methods
6.2.1. Vegetable production
Tomatoes (Leucopersicon esculentum, cultivar malgrove) were grown during the
summer season of2001 at the experimental fields of the Alemaya University, in Eastern
Ethiopia. The agro climatic conditions of the site and its location were described in
Chapter 5, section 5.2.3. ComCat® was administered by spraying tomato seedlings just
before transplantation, and a second time at the start of flowering, with 109. ha-I in 350
Iwater and, control plants with 0 g. ha-I. All other agricultural practices were the same
as those normally practiced by the University Farm Management Department during
tomato production. Tomatoes were manually harvested at a green mature stage and
immediately transported from the Alemaya University Campus to the Dire Dawa
University Fruit and Vegetable Research Center, which is 30 km away. To protect the
205
Chapter 6. Tomato storage (EC)
tomatoes against mechanical injury during transportation, tomatoes were packed in
plastic crates.
6.2.2. Postharvest treatment
The postharvest treatments, such as washing, disinfecting and packaging, were
according to the procedures described in Chapter 3, section 3.2.2. Tomatoes with visible
defects were discarded. After washing, both ComCat® treated and untreated tomatoes
were subjected to one of the following postharvest dipping treatments discussed in
Chapter4:
• dipping in chlorinated water (100flg. mrl chlorine, made with 5% NaOCI) at
ambient temperature for 20 minutes, packaged in Xtend® Film (see Chapter
3, section 3.2.2) and stored in;
• dipping in chlorine supplemented water, unpackaged and stored in EC;
• water washed, packaged in Xtend® Film and stored in EC;
• water washed, unpackaged and stored in EC;
• water washed, packaged in Xtend® Film and stored at ambient conditions, to
serve as a postharvest control;
• water washed and stored under ambient conditions without packaging, to
serve as a postharvest control.
These treatments were performed in three different containers, each as a replication
for each treatment group. After washing and dipping treatments, the surfaces of
tomatoes were drip dried to avoid the occurrence of condensation inside the packages.
Tomatoes were packed in 2 kg packages or unpackaged groups. Randomly, 2 kg
samples of packaged or unpackaged tomatoes were taken from each of the 12 treatment
replications and subjected to physiological, microbiological and chemical analyses on
each sampling time. Due to limited facilities, not all analyses could be carried out at all
sampling times. PWL and percentage marketability were determined on days 0, 4, 8, 12,
16, 20 and 24. Changes in juice content, TSS and pH were determined on days 0, 8, 16
and 24. The TTA, reducing sugar, total sugar, total aerobic bacteria and fungi
population were determined on days 0, 8, and 16. Seventeen tomatoes from each
206
Chapter 6. Tomato storage (EC)
treatment and replications were stored separately and used for subjective quality
analysis.
6.2.3. Temperature and relative humidity measurement
The storage temperature and relative humidity of air inside the EC as well as of the
ambient conditions was monitored according to the methods described in Chapter 5,
section 5.2.2.
6.2.4. Physiological weight loss, moisture and juice content
The analysis of PWL was conducted as described in Chapter 4, section 4.2.4.
Moisture content and juice content were conducted as described in Chapter 5, sections
5.2.6 and 5.2.7., respectively.
6.2.5. Chemical analysis
6.2.5.1. pH, total titratabie acidity (TT A) and total soluble solid (TSS)
The pH and TSS of tomatoes during the storage period were measured as described
in Chapter 4, sections 4.2.5.1 and 4.2.5.2, respectively. The TTA was determined
according to the procedures described in Chapter 4, section 4.2.6.1.
6.2.5.2. Sugar analysis
Estimation of reducing and total sugars were carried out according to the methods
described in Chapter 5, section 5.2.8.
6.2.6. Microbiological analysis
6.2.6.1. Total aerobic bacteria and fungi
The populations of aerobic bacteria and fungi were determined according to the
procedures described in Chapter 3, section 3.2.6.
6.2.7. Subjective quality analysis
The subjective quality analyses were made according to the procedure described in
Chapter 4, section 4.2.7. Marketable quality of tomatoes was evaluated according to the
207
Chapter 6. Tomato storage (EC)
scoring method used by Mohammed et al. (1999). The details of the method were given
in Chapter 4, section 4.2.7. In this case, emphasis was given to visually observable
decay and loss of firmness.
6.2.8. Data analysis
The experimental design and data analyses were according to the methods described
in Chapter 3, section 3.2.7. In Chapter 3 the statistical analysis of the disinfecting
treatment was coupled with MAP in order to see the overall effect of these treatments
on the quality parameters. During the current investigation, the statistical analysis of
MAP was coupled with storage temperature to look at their combined effect on the
quality parameters. Here the individual effect of MAP and storage temperature
treatments was analyzed, using multiple comparison of each treatment means by mean
separation of Duncan's multiple range tests.
6.3. Results and Discussions
Due to limited facilities at Alemaya University, Ethiopia, it was not possible to carry
out the same analyses as reported in Chapter 3. Some different analyses, such as
moisture content and juice content, were carried out, as well as alternative analyses such
as reducing sugars. It was also not possible to collect samples or carry out all the
analyses on the same day, as was managed in Chapter 3.
6.3.1. Temperature and relative humidity
Fig. 6.1. shows the dry bulb temperature and relative humidity changes against
storage period. The ambient air-dry bulb temperature was 25 - 36.5°C with the average
being 32°C during the 24 days of storage. The dry bulb temperature of the air inside the
EC was found to be from 14.4 - 23.5°C with the average being 20.5°C during the
storage period. An average drop in dry bulb temperature of 11.5°C was observed in this
study. The air temperature is an important factor for controlling tomato flesh
temperature.
208
Chapter 6. Tomato storage (EC)
(a) 6 am (d) 12 am
35 100 40 100
90
30 80 35 80 s-,
9 70 ~ u:-§ ~ 30 ~
~ 25 60 " ~ 603 3"
;":; 50 ,r:; ~,0 Ë" 25
,r:; ~
<
g_ 20 • .". 40 .:J: " 40 ."ec,E .. •••••••• .JI. -•. 30 ;:;u E 20 ;;. 'il. , .. ,.".. u" • ii 0:: 20 cx:15 20 15
10
10 0 10 0
6 11 16 21 26 6 11 16 21 26
Storage time (days) Storage time (days)
(e) 2 pm
(b) 8 am 100
40 100 40
90
35 3580 80,.., G ~
G~ 30 . 70
§
'6 ~ 30 E
~ ·60 .~ ~
60
::> ::>,r:;
::>
25 50 ,r:; ,0 '§
25 <J ~
ë 0' 40 .e
oc. 40 .
":: ~ c". 20 ;;
;:; 20
;:;
30 u ";:; uI- 20 0::
I- 0:: 15
15 2010 10· 0
10 0 6 11 16 21
6 11 16 21 26
Storage time (days) Storage time (days)
(c) 10 am (1)4 pm100 40 100
90 ;IC 9035
80 80 ~.
c-,
u 70 9 30 70 e-,~30 :-§
<U 60
:; E "
60 :-§
:;
::> 25 50 §
ë ,r:;25 50 ~ ë ,r:;
c". 40 .":: "c.
40 v
E 20 ;; E 2030 " 30
::
;;
I" u u- 0:: 15 20 0::
15 20 1010
0 10
0
10 16 21 26
6 11 16 21 26
6 11
Storage lime (days) Storage time (days)
19) 6 pm 100
E 80 ~§
~ 60 E
::> 25 ::>,r:;
ë 'I"O'
"c. 20 40 .:
":: ~
E ;:;
" 20 uI- 15 0::
10 . _.~--<~,- -_.-_-- -- -.- 0
6 11 16 21 26
Storage time (days)
__ Tdb-ambient _..• - - - Tdb-cooler
-----.-- RH-ambient - .. ~ ... RH-cooler
Figure 6.1. Temperature (0C) and relative humidity (%) of the environmental air and the
air inside the EC during tomato storage at 6 am (a), 8 am (b), 10 am (c), 12 am (d), 2 pm
(e), 4 pm (f) and 6 pm (g).
209
Chapter 6. Tomato storage (EC)
(a)
40
o Tdb-ambiem I
35 r- r-- Io Tdb-cooler r-- I
Q r-- r--30 Ir--
Q..). r-- !
~ 25 \,
l-
Q) I-- -
- - I--~ 20 --Q) -~ 15 :i
E I
~ 10 I
5 I
I
o I-
Day time
Figure 6.2. (a). The effect of daytime on the average environmental and evaporative
cooler temperatures (OC) during storage of tomatoes.
(b)
100
90 o RH-arrf:>ient DRH-cooler- r-- - -~ 80 r-- - r--~ I<:_,
.~ 70 :
-0
.~ I60
..c
<U
.>~ 50
r-
r- 0-
~ 40 r- r-
<U 0-
o!J r--
o:l 30
<U
>
< 20 !
10
'r-~ 'r-~ .t ~~ ~~ ~~
<br$' .~ ",r$' t:;.r$' 'Cr$'-c~r$' v'
Day time
Figure 6.2. (b). The effect of daytime on the average environmental and evaporative
cooler relative humidity (%) during storage of tomatoes.
210
Chapter 6. Tomato storage (EC)
Higher temperatures increase the tissue temperature of tomatoes, which initiate
biological and biochemical processes responsible for postharvest quality deterioration.
Fresh horticultural commodities respire at rates which double, triple, or even quadruple
for every 10°C increase in temperature (Sargent et al., 1991). It was therefore possible
to reduce the temperature inside the EC by more than 10°C during storage (Figure 6.1),
which in turn should have reduced the respiration rate of the tomatoes during storage.
The relative humidity of the environmental air during the storage period was between
24.0% and 62.2% with an average of 40.0%. The relative humidity of the air inside the
EC was 73.0 - 92.0% with an average of 83.9% during the storage period. The average
difference between the inside and outside relative humidity during the storage period
was 43.9% (Figure 6.1).
During the storage period, the highest mean temperature and nummum relative
humidity of ambient air were found to be at 12:00 AM (Figure 6.2 (a) and (b)). As can
bee seen in the figure, the average temperature increased with time from 6:00 to 12:00
AM and starts to slightly drop thereafter. The results presented in Chapter 5 gave
similar results.
6.3.2. Physiological weight loss (PWL), moisture content and juice content
Table 6.1 shows the PWL of tomatoes stored under evaporative cooling as well as
ambient temperature. The PWL was higher in tomatoes stored at ambient temperature.
While the PWL was between 10% and 13.5% for MAP tomatoes in EC after 24 days,
the same PWL was reached within 16 days at ambient temperature storage.
Preharvest treatment had a significant effect (p ~ 0.05) on PWL of the tomatoes. The
PWL of ComCat® treated tomatoes seemed to be more during storage at ambient
temperature. However, the PWL of disinfected and packaged ComCat<iYtreated tomatoes
was more up to 24 days of storage in EC.
211
Chapter 6. Tomato storage (EC)
Table 6.1. Changes in physiological weight loss of tomatoes stored in evaporative cooling
chamber and ambient temperature (RT) for 24 days.
Phvsiologicalloss in weight (%)
Treatment Day4 Day 8 Day 12 Day 16 Day 20 Day24
ComCat®, Ch, MAP, EC 1.660 b 3.437 ede 5.168 ed 7.343
ede 9.037 be 10.474 ede
Control, Ch, MAP, EC 1.260 b 2.819 de 4.590 ef 6.208 de 9.641 he 13.414 ab
ComCat®, Ch, EC 1.823 b 3.445 ede 4.733 de 7.714 b 9.942 b 12.079 bed
Control, Ch, EC 2.436 b 4.951 ab 6.384 be 8.417 e 11.157
a 13.744 ab
ComCat®, H20, MAP, EC 1.078 b 2.841 de 4.992 ede 7.474 ede 8.944 e 9.717 def
Control, H20, MAP, EC 1.577 b 3.133 de 4.873 ede 7.086 ede 9.796 b 12.106 abe
ComCat®, Ch, MAP, RT 3.473 a 6.807 ab 10.578 a 12.965 ab -
Control, Ch, MAP, RT 3.059 ab 5.720 ab 8.828 b 11.758 ab -
Comf.at", H20, EC 1.889 b 3.862 abc 4.790 ede 7.239 de 10.804 ab 13.790
a
Control, H20, EC 1.978 b 3.563 bed 6.052 ed 8.332 c 10.294 b 12.559 abc
Comf.at'", H20, RT 3.225 ab 7.600 a 9.531 ab 13.244 a
Control, H20, RT 3.459 a 6.375ab 11.117
a 13.172 ab -
Significance
Preharvest treatment (A) *
Disinfecting treatment (B) NS
Packaging + Storage temperature (C) ***
AXB NS
AXC ***
BXC NS
AXBXC NS
NS. *, *** Nonsignificant or significant at P ::;0.05 or 0.001 respectively. Means within a column followed by
the same letter(s) are not significantly different according to Duncan's multiple range test (P < 0.05). The
coefficient of variation and standard error were 0.166 and 0.791 resEectivel~. LSD Value = 2.213.
During 24 days of storage, the cumulative effect of modified atmosphere packaging
and storage conditions were highly significant (p :S0.001) on the response of tomatoes
to PWL. The moisture loss was significantly (p:S 0.001) reduced with the help of MAP,
reduced temperature and increased relative humidity during storage. It is known that EC
reduces the loss of moisture, PWL and loss of juice content (Lingaiah and Huddar,
1991; Sunil et al. 1997; Ashok et al., 1999), which was also confirmed in the present
212
Chapter 6. Tomato storage (EC)
study. Prepackaging dipping treatments of tomatoes, either in chlorinated water or
washing in tap water, had no significant (p > 0.05) effect on the PWL of tomatoes. The
interaction between preharvest treatments, MAP and storage temperature for the PWL,
during the 24 days of storage, was significant (p ~ 0.001).
Table 6.2. Changes in juice content of tomatoes stored in evaporative cooling chamber
and ambient temperature (RT) for 24 days.
Juice Content (%)
Treatment DayO Day 8 Day 16 Day24
Comf'at'", ch, MAP, EC 64.698 a 61.138 ab 60.178 ab 59.046 a
Control, ei; MAP, EC 61.796 ab 61.007 ab 56.985 abc 55.610 abc
Comï.at", ei; EC 64.698 a 59.739 be 52.674 ed 43.689 def
Control, Ch, EC 61.796 ab 54.291 bed 48.010 de 40.259 fg
ComCat®, H20, MAP, EC 64.698 a 64.310 a 63.787 a 57.825 ab
Control, H20, MAP, EC 61.796 ab 59.961 be 53.514 bed 52.284 bede
ComCat®, Ch, MAP, RT 64.698 a 53.763 bed 52.325 cd
Control, Ch, MAP, RT 61.796 ab 47.818 def 45.761 de
Cornf'at",H20, EC 64.698
ab
a 61.499 abc 59.113 57.483 ab
Control, H20, EC 61.796 ab 57.581 abc 50.682 ede 50.612 bede
ComCat®, H20, RT 64.698 a 48.954 def 32.184 fgh
Control, H20, RT 61.796 ab 42.736 fg 35.917
fg
Significance
Preharvest treatment (A) NS
Disinfecting treatment (B NS
Packaging + Storage temperature (C) ***
AXB NS
AXC NS
BXC ***
AXBXC *
NS, *, *** Nonsignificant or significant at P ::; 0.05 or 0.001 respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test
(P < 0.05). The coefficient of variation and standard error were 0.088 and 0.935 respectively. LSD
Value = 7.775.
213
Chapter 6. Tomato storage (EC)
At harvest, the moisture content oftomatoes was found to be 94.42% and 93.98% for
ComCat® treated and untreated samples, respectively, and remained above 90% during
storage, with not much variation during the 24 days of storage, irrespective of the
storage conditions. The recorded data are therefore not shown.
At harvest, the juice content was higher in ComCat® treated than in control tomatoes
(Table 6.2), although not significant (p > 0.05). Although only significant in some
cases, the ComCat® treated tomatoes maintained a higher juice content throughout the
storage time in the EC. The packaging and storage temperature were the most important
factors affecting the juice content of tomatoes and was highly significant (p :s 0.001).
The interaction between disinfecting, MAP and storage temperature was highly
significant (p:S 0.001) on the changes in juice content oftomatoes during the 24 days of
storage. During the same interval, the three-way interaction between pre- and
postharvest treatments on the changes of juice content of tomatoes, subjected to
different pre- and postharvest treatments, was significant (p :s 0.05). In Chapter 5 it was
noted that changes in PWL, moisture content and juice content of carrots indicated the
same thing, i.e. loss of water, while these parameters show individual changes in
tomatoes. The reason could be ascribed to the protective skin of the tomato, which
prevents moisture loss, while carrots have an absorbing surface that will also give off
moisture easily.
6.3.3. Chemical changes
6.3.3.1. Total soluble solid (TSS)
The ComCat® treatment did not have a significant (p > 0.05) effect on the TSS of
tomatoes at harvest (Table 6.3), but the effect was significant in a few samples (p :s
0.05) during storage. In general, the TSS increased during storage from around 4.6
°Brix to almost 5.5 °Brix in some cases. The results showed that the TSS content of
ComCat® treated tomatoes generally remained higher during 24 days of storage in EC,
compared to the control tomatoes. The changes in TSS were found to be faster in fruits
214
Chapter 6. Tomato storage (EC)
stored at ambient conditions, which is supported by the work ofWaskar et al. (1999) for
pomegranate.
Table 6.3. Changes in total soluble solids of tomatoes stored in evaporative cooling
chamber and ambient temperature (24) for 24 days.
Total soluble solid (OBrix)
Treatment DayO Day8 Day 16 Day24
ComCat®, ei; MAP, EC 4.575a 4.867 abed 4.700 ede 5.l33 abe
Control, ei;MAP, EC 4.690a 4.883 abed 4.500 abed 4.767 ede
Comf'at", Cb, EC 4.575 a 5.333 a 5.483 a 5.483 a
Control, ei, EC 4.690a 4.700 bed 4.367 ede 4.550 de
Comf'at", H20, MAP, EC 4.575 a 5.417
a 5.093 abe 4.867 abed
Control, H20, MAP, EC 4.690 a 4.800 bed 4.933 de 4.850 bed
Cornï.at'", Ch, MAP, RT 4.575 a 5.100 ab 4.917 ab
Control, er; MAP, RT 4.690a 4.967 abed 4.533 bed
Comf.at'", H20, EC 4.575 a 4.267 d 5.000 abed 4.900 abed
Control, H20, EC 4.690 a 4.717 bed 4.733 abed 4.733 ede
Comï.at", H20, RT 4.575 a 4.800 bed 5.193 ab
Control, H20, RT 4.690a 5.067 ab 4.867 abed
Significance
Preharvest treatment (A) *
Disinfecting treatment (B) NS
Packaging + Storage temperature (C) NS
AXB NS
AXC NS
BXC *
AXBXC *
NS, *Nonsignificant or significant at P $ 0.05. Means within a column followed by the same letter(s) are
not significantly different according to Duncan's multiple range test (P < 0.05). The coefficient of
variation and standard error were 0.065 and 0.027 respectively. LSD Value = 0.505.
Surprisingly, the effect of MAP and storage temperature on the TSS content of
tomatoes was not significant (p > 0.05). The change in TSS is one of the important
postharvest parameters used to evaluate the quality of carrots (see Chapter 3) during
storage. Comparing tomatoes with carrots, the rapid change in TSS content of carrots,
215
Chapter 6. Tomato storage (EC)
could be due to the higher PWL of the carrots (see Chapter 3 and 5). Jauregui et al.
(1999) have shown that these two parameters are linearly correlated.
The interactive effect of prepackaging chlorinated water disinfecting, MAP and
storage temperature on the changes of TSS of tomatoes during storage was significant
(p :s 0.05). Similarly, the three-way interaction between pre- and postharvest treatments
on the changes of TSS was also significant (p :s 0.05). In general, there was a positive
effect of pre- and postharvest treatments on the TSS content of tomatoes stored in EC,
when compared to the TSS content oftomatoes stored at ambient conditions.
6.3.3.2. pH
At harvest the pH of ComCat® treated and control tomatoes were not significantly (p
> 0.05) different. There were also no significant (p > 0.05) differences in the changes in
pH values of ComCat® treated and control tomatoes during the 24 days of storage
(Table 6.4). The pH of tomato juice increased continuously with the progress in storage
period, regardless of pre- or postharvest treatments, from around 4.1 to as high as 4.6,
which is in agreement with the results reported by Mohammed et al. (1999). The
prepackaging chlorine disinfecting had a significant effect on the pH values of tomatoes
during storage.
After 24 days in EC, the pH of disinfected, packaged tomatoes was significantly (p $;
0.05) higher than the pH of water washed ComCat® treated tomatoes. The pH remained
significantly (p $; 0.05) higher in unpackaged, disinfected control tomatoes, compared to
the ComCat® treated ones after 24 days in EC. However, the opposite trends were
observed in the case of water washed, unpackaged control, as well as ComCat® treated
tomatoes stored in EC for 24 days.
During 8 days of storage, the packaged or unpackaged tomatoes stored at ambient
temperature, displayed a lower pH, compared to those stored in EC. After 24 days of
storage, the pH of tomatoes was significantly (p $; 0.05) higher in packaged samples
stored in EC, than that of unpackaged ones stored under similar conditions. This could
216
Chapter 6. Tomato storage (EC)
be associated with the higher rates of respiration at relatively higher storage
temperature, since acid is produced from catabolism of sugar, which will be shown later
in this Chapter.
Table 6.4. Changes in pH of tomatoes subjected to different pre- and postharvest
treatments and stored in evaporative cooling chamber and ambient temperature (RT) for
24 days.
PH
Treatment DayO Day8 Day 16 Day24
Comf.at'", Ch, MAP, EC 4.111 a 4.253 ab 4.347 be 4.625 a
Control, ct, MAP, EC 4.109 a 4.270 a 4.393 ab 4.640a
ComCat®, ei, EC 4.111 a 4.213 abc 4.180rgh 4.180 ij
Control, Ch, EC 4.109 a 4.273 a 4.357 ab 4.490 be
ComCat ®.ci, MAP, RT 4.111 a 4.180 cd 4.417 a
Control, C12, MAP, RT 4.109 a 4.217 abc 4.273 ed
Cornf'at'", H20, MAP, EC 4.111 a 4.220 abc 4.360 ab 4.477 bed
Control, H20, MAP, EC 4.109 a 4.260 ab 4.407 a 4.510 b
fg
Comf.at'", H20, EC 4.111 a 4.187 abc 4.243 def 4.317
Control, H 0, EC 4.109 a 4.223 abc 4.210 efg 4.210 hi2
ComCat®, H20, RT 4.111 a 4.177 bed 4.270 ede
Control, H20, RT 4.109 a 4.147 cd 4.200 erg
Significance
Preharvest treatment (A) NS
Disinfecting treatment (B) *
Packaging + Storage temperature (C) ***
AXB NS
AXC ***
BXC NS
AXBXC ***
NS, *, *** Nonsignificant or significant at P s 0.05 or 0.001 respectively. Means within a column
followed by the same letter(s) are not significantly different according to Duncan's multiple range test (P
< 0.05). The coefficient of variation and standard error were 0.011 and 0.0258 respectively. LSD Value =
0.073.
217
Chapter 6. Tomato storage (EC)
The interactive effect of preharvest ComCat® treatment, packaging and storage
conditions on the pH values of tomatoes was significant (p ~ 0.001). Similarly, the
three-way interaction between all the pre-and postharvest treatments on the changes of
pH values oftomatoes was highly significant (p ~ 0.001).
6.3.3.3. Total titratabie acidity (TTA)
The TTA decreased dramatically in the tomatoes during ripening from the green
mature to the red mature stages during 16 days of storage, from around 0.6 to as low as
0.4 (Table 6.5), confirming the results of Shi et al. (1999). However, the TTA-values
obtained in the current study were relatively higher than those reported, as well as those
observed in Chapter 4, which could be due to the different growing practice or climate
and soil type. At harvest, the TTA was higher in ComCat® treated tomatoes than in the
control fruit, which is similar to the data presented in Chapter 4, however, not
significant (p > 0.05) in this case. The effect of higher TTA on microbial populations
associated with ComCat® treated tomatoes, compared to the controls, was evident here
as well as in Chapter 4, and is confirmed by the work of Mohammed et al. (1999). After
16 days storage, the TTA of ripe tomatoes was generally higher in ComCat® treated
tomatoes than in the controls, suggesting that ComCat® treatment resulted in more
acidity to protect against microbiological proliferation. Microbiological data is shown in
section 6.1.2.
The TTA declined at a faster rate in controls than in ComCat® treated tomatoes
during storage. The reduction in TTA in ComCat® treated whole tomatoes subjected to
different postharvest treatments, and stored inside the EC for 16 days, varied from
22.5% to 27.9%. During the same interval, the reduction in ITA in control tomatoes,
subjected to the same postharvest treatments, varied between 26.4% and 34.1%.
However, the difference in TTA was not significant (p > 0.05). After 16 days of storage,
the highest loss of TTA in tomatoes stored at ambient temperature and humidity, was
evident from the results presented in Table 6.5. The TTA in packaged ComCat® treated
tomatoes dipped in chlorinated water and stored at ambient conditions was reduced by
218
Chapter 6. Tomato storage (EC)
32.3%, whereas the control tomatoes, subjected to the same postharvest treatment, had
lost 34.4%. The TTA in unpackaged ComCat® treated and control tomatoes was
reduced by 35.0% and 39.0%, respectively. These results showed that, the higher the
storage temperature of fruit, the higher the reduction in the TTA during ripening and
storage. This could be associated with rapid ripening and senescence properties of
tomatoes when stored at higher temperatures.
Table 6.5. Changes in total titratable acidity of tomatoes subjected to different pre-
and postharvest treatments and stored in evaporative cooling chamber and ambient
temperature (RT) for 16 days.
Total titratabie acidity (mg citric acid/I 00 g)
Treatment DayO Day8 Day 16
Comï.at", ei, MAP, EC 0.663a 0.628 a 0.487 ab
Control, ei;MAP, EC 0.637 ab 0.621 a 0.444 abc
ComCat®, C12,EC 0.663 a 0.538 abed 0.490 ab
Control, Ch, EC 0.637 ab 0.487 ede 0.420 be
Cornf'at'", H20, MAP, EC 0.663 a 0.536 abed 0.478 ab
Control, H20, MAP, EC 0.637 ab 0.516 bede 0.465 ab
Cornï.at'", Ch, MAP, RT 0.663 a 0.590 abc 0.449 abc
Control, ei;MAP, RT 0.637 ab 0.570 abc 0.418 be
ComCat®, H20, EC 0.663 a 0.505 bede 0.514 a
Control, H20, RT 0.637 ab 0.496 ede 0.389 c
ComCat®, H20,RT 0.663 a 0.586 abc 0.431 abe
Control, H20, EC 0.637 ab 0.607 ab 0.469 ab
Significance
Preharvest treatment (A) NS
Disinfecting treatment (B) NS
Packaging + Storage temperature (C) NS
AXB NS
AXC NS
BXC *
AXBXC NS
NS, * Nonsignificant or significant at P ~ 0.08 respectively. a, b. c. ct, e Means within a column followed
by the same letterïs) are not significantly different according to Duncan's multiple range test (P <
0.05). The coefficient of variation and standard error were 0.100 and 0.012 respectively. LSD Value =
0.089.
219
Chapter 6. Tomato storage (EC)
6.3.3.4. Sugar changes during storage
The total sugars decreased during the storage period (Table 6.6). Similar trends of
decreasing total soluble sugar content in tomatoes were observed in Chapter 4. At
harvest the total sugar content was significantly higher (p ~ 0.05) in ComCat® treated
tomatoes, compared to the controls, and remained higher ( p ~ 0.05) throughout all the
postharvest treatments, and during 16 days of storage in EC. Again, this could be an
indication of delayed ripening effected by the preharvest ComCat® treatment, while the
sugar content was rapidly depleted in control tomatoes, due to faster ripening. The total
sugars decreased rapidly in the control tomatoes stored at ambient conditions, compared
to those stored in EC. In this case the EC retarded the ripening and senescence process,
while the respiration and metabolism of tomatoes stored at ambient temperature was
high, and utilized much of the available sugar.
At harvest the control tomatoes contained a higher content (p ~ 0.05) of reducing
sugars, compared to the ComCat® treated ones, and remained so during storage (Table
6.6). In general, the reducing sugars decreased during 16 days of storage. The
preharvest ComCat® treatment had a significant (p ~ 0.05) effect on the changes of
reducing sugar contents of tomatoes during storage in EC, while the reducing sugar
decreased faster in the controls. This could be due to a higher respiration rate of the
control tomatoes, and corresponds to the results obtained in Chapter 3, where it was
shown that the content of glucose increased more in ComCat® treated tomatoes.
The calculated non-reducing sugar content increased during the first 8 days of
storage, and was followed by a faster decline in some of the tomatoes subjected to
different postharvest treatments. After 8 days of storage, ComCat® treated tomatoes had
a higher content of non-reducing sugars, but after 16 days storage, this trend was not
observed for the disinfected samples.
220
Chapter 6. Tomato storage (EC)
Table 6.6. Changes in reducing, non-reducing and total sugar contents of tomatoes stored in the evaporative cooling chamber and
ambient temperature (RT) for 24 days.
Treatment Total Sugar (g/IOOg) Reducing Sugar (gil OOg) Non-reducing Sugar (giiOOg)
Da~O Day 8 Day 16 DayO Day8 Da~ 16 DayO Day 8 Day 16
CorrrCat'", er, MAP, EC 5.101 a 4.665 ab 4.444 ab 3.86rb 2.517 be 3.206 a 1.233 a 2.148 abc 1.238 cd
Control, Ch, MAP, EC 5.227 ah 3.722 de 2.535 e 3.988 a 2.527 he 1.174 e 1.240 a 1.195 de 1.361 bed
Cornf.at'", Ch, EC 5.101 a 4.489 abc 3.706 e 3.867 ah 1.629 d 3.084 ah 1.233 a 2.860 a 1.380 he
Control, Ch, EC 5.227 ah 3.834 ede 3.027 de 3.988 li 1.727 cd 1.644 de 1.240 a 1.584 cd 1.333 bed
Comf'at'", H20, MAP, EC 5.101 a 4.902 a 4.917a 3.867 ah 2.929 a 2.304 hed 1.233 a 1.973 de 2.613 a
N Control, H20,MAP, EC 5.227 ah 4.106 bed 3.502 cd 3.988 a 2.329 be 2.075 cd 1.240 a 1.777 ed 1.427 bed
N
Comï.at", H20, RT 5.101a 4.282 bed 4.006 he 3.867 ah 2.755 ab 2.878 abc 1.233 a 1.527 ede 1.127 cd
Control, H20, RT 5.227 ah 3.399 ef 1.665 r 3.988 a 1.958 e 1.504 de 1.240 a 1.440 ede 0.161 der
Significance Total Sugar Reducing Sugar Non-reducing sugar
Preharvest treatment CA) * * *
Disinfecting treatment (B) NS NS NS
Packaging and storage temperature (C) *** NS NS
AXB NS NS *
AXC NS NS NS
BXC ** NS **
AXBXC * NS NS
NS, ., .. , ... Nonsignificant or significant at P ~ 0.05,0.01 or 0.001 respectively. Means within a column followed by the same letter(s) are not significantly
different according to Duncan's multiple range test (P < 0.05). The coefficient of variation and standard error were 0.155 and 0.047 for reducing sugar, 0.322
and 0.266 for nonreducing sugar and 0.088 and 0.218 for total sugar respectively. LSD Value = 0.723, 0.760 and 0.622 for reducing, nonreducing and total
sugar respectively.
Chapter 6. Tomato storage (EC)
The two-way interaction between postharvest treatments, i.e. disinfecting and Map +
storage temperature, had a significant (p ~ 0.01) effect on the changes in total sugar and
non-reducing sugar in tomatoes during 16 days at EC temperature. The two-way
interaction between the preharvest ComCat® treatment and disinfecting also had a
significant (p ~ 0.05) influence on the changes in non-reducing sugar. Similarly, the
three-way interaction between the preharvest treatment, disinfecting and Map + storage
temperature on the changes of total sugar content of tomatoes was significant (p ~ 0.05)
during storage. These results thus demonstrated that ComCat® treatment in general has
an effect on the sugar content of tomatoes.
6.3.4. Microbiological changes
6.3.4.1. Total aerobic bacteria
Table 6.7 shows the changes in population of total aerobic bacteria in tomatoes
during storage. The numbers of aerobic bacteria in tomatoes disinfected in chlorinated
water were significantly (p ~ 0.001) decreased and remained low only up to 8 days, but
then increased during storage in EC. Their growth was not suppressed to the same
extend as those of low temperature refrigerated storage (see Chapter 5). MAP + storage
temperature had a significant (p ~ 0.001) effect on the estimated population of total
aerobic bacteria during the storage of tomatoes in EC. Compared with the other
postharvest treatments, chlorinated water treatment coupled with MAP, were the best
for both reducing and limiting the growth of aerobic bacteria during storage.
The population of aerobic bacteria was higher in packaged fruits washed in water
than in unpackaged tomatoes subjected to chlorine disinfecting during storage in the
EC. This clearly showed the danger of using MAP at higher storage temperatures.
Obviously, the humidity in the headspace air of packaged products is high, and creates
favourable conditions for the proliferation of microorganisms in packaged fruit and
vegetables. The results therefore show that commodities should be disinfected prior to
storage in EC. It should, however, be noted that, although water washed packaged
tomatoes showed higher total aerobic bacteria populations than disinfected ones, the
222
Chapter 6. Tomato storage (EC)
quality of the fruit remained good, in the sense that no increased spoilage of edible flesh
was noted.
Table 6.7. Populations of total aerobic bacteria in tomatoes packaged or unpackaged and
stored in evaporative cooling chamber or at ambient temperature (RT) for 16 days.
Total aerobic bacteria
Treatment DayO Day8 Day 16
CornCat", Cb, MAP, EC 4.995 ab 3.146 f 3.763 f
de
Control, C12,MAP, EC 5.089a 3.646 ef 4.115
ComCat'", Cb, EC 4.995 ab 4.204 de 4.706 bed
Control, Ch, EC 5.089 a 4.155 de 4.528 ede
Comf'at", H20, MAP, EC 4.995 ab 5.617 abe 5.227 ab
Control, H20, MAP, EC 5.089a 5.850 ab 5.397 a
CorrrCat'", H 0, EC 4.995 ab 5.945 ab 5.037 abc2
Control, H20, RT 5.089 a 6.187 a
Significance
Preharvest treatment (A) NS
Pre packaging treatment (B) ***
Packaging + storage temperature (C) ***
AXB NS
AXC NS
BXC NS
AXBXC *
NS, *, *** Nonsignificant or significant at P ::; 0.05 or 0.00 I respectively. a. b. c. d, c, f Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple
range test (P < 0.05). The coefficient of variation and standard error were 0.064 and 0.088 respectively.
LSD Value = 0.522.
ComCat® had no significant (p > 0.05) effect on the aerobic bacteria in this
experiment, although the aerobic bacteria population was higher in control than in
ComCat® treated fruits at harvest, but not significantly (0 > 0.05). This coincides with
the TTA being higher in ComCat" treated tomatoes, although also not significant (p >
0.05), which was also observed in the work in Chapter 4. The three-way interaction
223
Chapter 6. Tomato storage (EC)
between the preharvest ComCat® treatment and postharvest treatments was significant
(p ~ 0.05) on the changes in total aerobic bacteria during storage in the EC.
6.3.4.2. Total moulds and yeasts
The populations of moulds and yeasts was less on ComCat® treated tomatoes,
although it had no significant (p > 0.05) effect on their numbers, both at harvest and
during storage (Table 6.8). The number of moulds and yeasts on tomatoes decreased
after disinfecting, as well as water washing, and stayed low up to 8 days in EC. The
prepackaging disinfecting treatment was highly significant (p ~ 0.001) on the
populations of moulds and yeasts during storage of tomatoes. These numbers stayed
suppressed on the chlorine disinfected tomatoes up to 16 days storage in the EC.
Table 6.8. Populations of moulds and yeasts in tomatoes packaged or unpackaged and
stored in the evaporative cooling chamber or at ambient temperature (RT) for 16 days.
Moulds and yeasts
Treatment DayO Day8 Day 16
Comf'at", er, MAP, EC 4.208a 3.144 d 3.326 d
Control, Ch, MAP, EC 4.186 a 3.844 ed 3.796 d
Cornï.at'", C12,EC 4.208 a 3.398 d 4.099cd
Control, ei, EC 4.186 a 3.451 d 4.350 bed
Comf'at'", H20,MAP, EC 4.208 a 3.787 d 5.121 abc
Control, H20, MAP, EC 4.186 a 3.845 cd 5.107abe
Comf'at", H20, EC 4.208 a 4.391 bed 5.107 abc
Control, H20, RT 4.186 a 6.046 a
Significance
Preharvest treatment (A) NS
Prepackaging treatment (B) ***
Packaging (C) **
AXB NS
AXC NS
BXC NS
AXBXC NS
NS, **, *** Nonsignificant or significant at P ~ 0.01 or 0.001 respectively. a. b. c. d Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple
range test (P < 0.05). The coefficient of variation and standard error were 0.155 and 0.128
respectively. LSD Value = 1.088.
224
Chapter 6. Tomato storage (EC)
The estimated number of moulds and yeasts highly increased in control tomatoes
stored at ambient temperature, indicating the benefit of EC and MAP on the storage
quality. The effect of MAP + storage temperature was highly significant (p ~ 0.001) on
the numbers of moulds and yeasts.
6.3.5. Subjective quality analysis
The percentage marketable tomatoes decreased rapidly during 12 days of storage at
ambient conditions (Table 6.9). After 12 days of storage at ambient conditions, the
packaged fruit were over 53% unmarketable. During the same interval, unpackaged
tomatoes stored at ambient conditions dropped to below 30% marketability, due to
excessive moisture loss, as well as decay. Similar findings were reported by Ashok et
al. (1999) who showed that unwrapped and wrapped tomatoes became unacceptable
after 3 and 10 days at ambient temperature respectively. According to this author, the
main reason for unacceptability of these tomatoes was PWL. However, in the current
study, over-ripening and soft rot were the most serious problems associated with
tomatoes stored at ambient temperature and humidity.
Tomatoes stored in the EC fared better, as the temperature inside the store was nearer
to the optimum temperature of 13°C for storage of tomatoes, than the ambient
temperature. Packaged tomatoes could then be kept for more than 24 days without loss
of freshness quality inside the EC. All packaged ComCat® treated tomatoes, as well as
controls, disinfected in chlorinated water were 100% marketable up to 12 days in EC
storage. After 12 days of storage, the percentage marketability of these fruit remained
higher than 96%.
Preharvest ComCat® treatment had no significant effect on the marketability of
tomatoes after storage in the EC, but the interactive effect of pre- and postharvest
treatments on the marketability of tomatoes was found to be significant at p ~ 0.05. The
percentage marketable ComCat® treated, packaged tomatoes, disinfected in chlorinated
water, was found to be 3.7% higher than the control fruits subjected to the same
225
Chapter 6. Tomato storage (EC)
postharvest treatment. After 24 days at EC, the packaged ComCat® treated tomatoes
that were dipped in chlorinated water, showed the highest percentage marketability.
Table 6.9. Percentage marketable ComCat® treated and control tomatoes subjected to
different treatments after 4, 8, 12, 16, 20 and 24 days of storage at evaporative cooling and
ambient temperatures (RT) for 24 days.
Marketable tomatoes (%)
Treatment DayO Day4 Day8 Day 12 Day 16 Day20 Day24
Comf'at", ei,MAP, EC 100a 100 a 100 a 100 a 96.3 a 90.7a 83.3 a
Control, Ch, MAP, EC 100a 100a 100a 100a 92.6 ab 85.2 abc 79.6 ab
ComCat®, ei; EC 100a 100a 96.3 ab 90.7 abed74.1 ef 68.5 fgh 68.5 edef
Control, Ch, EC 100a 100a 100a 98.5 ab 87.0 abe 75.9 edef 64.8 efg
Con-Cat", ei, MAP, RT 100a 96.3 ab 75.9 cd 46.3 e 44.4 gh
Control, Ch, MAP, RT 100 a 92.6 ab 70.4 de 46.3 e 46.3 g
ComCat ®,H20, MAP, EC 100 a 100a 98.2 ab 96.3ab 92.6 ab 85.2 abc 75.9 abed
Control, H20, MAP, EC 100 a 100 a 100 a 98.5 ab 98.2 a 90.7a 77.8 abc
ComCat ®,H20, EC 100 a 100a 98.5 ab 92.6 ab 85.2 bed 70.4 efg 55.6g
Control, H20, EC 100a 100 a 96.3 ab 94.4 abc 75.9 de 66.7 fhg 59.3 fg
Comf'at", H20, RT 100a 85.2 c 64.8 ef 35.2 fg 27.81
Control, H20, RT 100 a 83.2 ed 61.1 f 31.5 g 29.61
Significance
Preharvest treatment (A) NS
Pre packaging treatment (B) *
Packaging + Storage temperature (C) ***
AXB NS
AXC NS
BXC ***
AXBXC *
NS, *, *** Nonsignificant or significant at P ~ 0.05 or 0.00 I respectively. a. b. c. d. e. f. g. h. i Means within a
column followed by the same letter(s) are not significantly different according to Duncan's multiple range
test (P < 0.05). The coefficient of variation and standard error were 0.070 and 1.276 respectively. LSD Value
= 9.045.
Previous studies by Acedo-AL Jr (1997) also showed that the pre-storage treatment
delayed the ripening and reduced incidence of decay, supporting the results obtained in
this study. It was noticed that a colour change from green, at harvest, to red was most
retarded in packaged tomatoes stored in the EC. These results therefore demonstrated
226
Chapter 6. Tomato storage (EC)
the importance of combining preharvest treatments aimed at increasing yield and
quality, with proper postharvest treatments, to improve the shelf life and maintain the
quality of perishable vegetables, such as tomatoes, under hot and dry climatic
conditions.
The results In Chapter 4 showed that the onset of senescence in unpackaged
ComCat® treated tomatoes that were not disinfected, was delayed, compared to the
controls. However, this was not the case in the hot dry climate of Dire Dawa, Ethiopia.
The higher relative humidity in the EC, which was higher than that of the room
temperature studies of Chapter 4, helped to improve the marketability. In the EC,
tomatoes were only 83% and 79% marketable after 24 days storage for the ComCat®
treated and control tomatoes, respectively, compared to the 75% and 77% at the room
temperature conditions of Chapter 4. The water washed samples showed a similar
difference.
6.4. Conclusions
An EC unit, that maintained a temperature between 14.4°C and 23.5°C and relative
humidity between 73.0% and 92% during storage, was used to store tomatoes. This
temperature was somewhat lower than the room temperature reported in Chapter 4,
which was between 16.9°C and 25.2°C, while the relative humidity was higher than the
62.2% recorded in Chapter 4. The higher humidity was advantageous for maintaining
some of the chemical quality characteristics, such as moisture content and TSS, but
seemed to favour microbial growth due to a combined effect with high temperature. The
quality parameters tested were maintained better in EC, and resulted in an extension of
over 70% in shelf life of tomatoes. This method has been shown to have great potential
for application in the study site in Ethiopia to reduce huge postharvest vegetable losses.
It is suggested that the EC air temperature can be reduced further, until it falls in the
range of 8-13°C, which is the optimum for tomato storage, by installing a multi-stage
EC pad connected in series.
227
Chapter 6. Tomato storage (EC)
At harvest, the green mature ComCat® treated tomatoes contained lower TSS,
reducing sugar, non-reducing sugar, and total sugar. These parameters also remained
higher in ComCat® treated tomatoes during storage in EC. The PWL and content of
TSS, total sugars, reducing sugars and non-reducing sugars were significantly (p :::;0.05)
affected by the preharvest ComCat® treatment during storage in EC. Preharvest
ComCat® treatment of tomato plants can therefore contribute to improve the quality of
tomatoes during storage in an EC.
Disinfecting treatment of tomatoes did not have any effect on the chemical
parameters during storage in the EC, although, the pH of tomatoes was significantly (p
:::;0.05) influenced by this treatment resulting in an increase in pH. The disinfecting
treatment significantly affected the postharvest microbial populations associated with
tomatoes stored in EC. Protection against microorganisms resulted in the marketability
of tomatoes being significantly higher (p :::;0.001). These results showed that the
postharvest disinfecting treatment was important to control decay, although not as
effective as at low temperature storage (Chapter 4). It is possible that the high humidity
of the EC contributed to the re-establishment of microorganisms.
MAP in microperforated Xtend® film, together with the storage temperature in the
EC, had a highly significant (p :::;0.001) effect on the PWL, juice content and pH of
stored tomatoes, but had no significant effect on the total, reducing and non-reducing
sugars, and TTA of the tomatoes. It had a highly significant (p :::;0.00 I) effect on the
total aerobic bacteria and moulds and yeasts during storage of tomatoes in the EC. MAP
+ storage temperature in EC reduced the rate of ripening of tomatoes and PWL during
storage, and resulted in significant (p :::;0.00 I) improvement of the marketability of
tomatoes. The microperforations associated with Xtend® film had several benefits, such
as preventing condensation and maintaining optimum gas levels for normal respiration.
The combinations of preharvest ComCat® treatment of tomato plants, disinfecting,
and MAP storage in EC, was shown to benefit the storage quality of tomatoes. A higher
juice content was obtained, higher contents of TSS and total sugars, lower pH and lower
228
Chapter 6. Tomato storage (EC)
growth of aerobic bacteria and better marketability, compared to the controls. However,
these parameters were not as good as was observed during low temperature storage of
tomatoes, as well as room temperature storage, reported in Chapter 4. Since the latter
room temperatures and the temperature in EC were almost the same, it seems as if the
high relative humidity when combined with relatively high EC temperature, used in this
chapter, may contribute to faster deterioration of tomatoes. Adaptation of the EC to
lower temperatures should therefore also incorporate alterations to address the relative
humidity, otherwise higher relative humidity ranging from 85% up to 90% are desirable
for tomato storage.
229
CHAPTER 7
GENERAL DISCUSSION and CONCLUSIONS
Preharvest treatment of plants with ComCat® was previously shown to increase the
yield of vegetables (Schnabl et al., 2001). The question arose how would these complex
plant growth regulators and natural metabolites in ComCat® affect postharvest handling
and storage of fruit and vegetables. According to the review in chapter 2, the
postharvest quality of fruits and vegetables are affected by preharvest conditions, e.g.
environmental conditions, fertilization practices, water management, plant growth
promoters, and integrated and ecological farming systems (Bialczyk et al., 1996; Gao et
al., 1996 and Carmer et a!., 2001). These reviews suggested that preharvest practices,
which improved yield, should be integrated with its postharvest quality performance.
Postharvest handling includes washing methods, normally with chlorine containing
solutions, to reduce microorganisms (Beuchat ef al., 1998; Escudero et al., 1999;
Beuchat et al., 2001; Ukuku and Sapers, 2001; Prusky et al. 2001), and packaging.
Although chlorine treatment is effective, alternative disinfecting methods, which are
environmentally friendly, are being sought (Wisniewski et al., 1992, Elmer and Gaunt,
1994, Wisniewski et al., 2001; Ben- Yehoshua et al. 2000). In this study, anolyte water
was investigated as such an alternative (Seyoum et al., 2002). For packaging, MAP was
selected for its 02 and CO2 regulation properties, and control of moisture loss without
occurrence of condensation (Exarna et al., 1993; Seyoum et al., 2001).
The aims of this study therefore were: (1) investigation of the effect of preharvest
ComCat® treatment on postharvest quality of stored carrots and tomatoes, (2)
investigation of the effect of pre-packaging disinfecting by anolyte and chlorinated
water on the quality of preharvest ComCat® treated and untreated control carrots and
tomatoes, (3) investigation of the storability of preharvest ComCat® treated carrots and
tomatoes using MAP and storage temperatures and (4) investigation of the use of
230
General Discussion and Conclusions
evaporative cooling techniques to reduce postharvest losses of both ComCat® treated
and untreated carrots and tomatoes in hot climatic regions, in this case, Ethiopia.
This study showed that MAP conserves postharvest physiological, chemical,
biochemical and microbiological qualities of carrots and tomatoes, resulting in
increased shelf life and marketability, when combined with proper storage conditions.
The results generally indicated that MAP highly reduced PWL, and improved contents
of TSS, total sugars, sugar/acid ratio and ascorbic acid of carrots and tomatoes. The
packaging reduced the rate of respiration and some metabolic processes of commodities,
and resulted in less utilisation of sugars as metabolic substrate, confirming the research
of Kader (1986) and Zagory and Kader (1988). As a general trend, the microbiological
flora of carrots and tomatoes were higher in unpackaged carrots and tomatoes stored at
lower temperatures. When MAP was combined with disinfecting treatments and proper
storage temperature, the control of microorganisms was successful. At room
temperature, MAP seemed to create conditions favourable for pathogens. The
marketability of tomatoes was significantly improved with packaging, since MAP
reduced the rate of respiration and some biochemical activities responsible for hastened
ripening of fruits (Kader, 1986). It was also shown that the benefits already gained from
the preharvest ComCat® treatment and anolyte water as a disinfectant can be maximised
by using MAP and proper storage temperature.
Storage temperature greatly influenced the concentrations of O2, CO2, and N2 in
packages of both tomatoes and carrots. The gas data clearly showed that the respiration
and metabolism of carrots and tomatoes were higher when stored at room temperature
than in cold storage (1°C or 13°C for carrots and tomatoes respectively). The respiration
rate, based on the gas dynamics, seemed to be distinctively different only during the
early active ripening stage of tomatoes, which is before the climacteric onset, stored at
13oe and room temperature (16.9 - 25.2°C). After full ripening, the concentrations of
gases became approximately equivalent, irrespective of storage temperatures. These
results thus suggested that proper temperature management is important for tomato
231
General Discussion and Conclusions
storage during the early stage of ripening of one or two weeks, in order to extend the
shelf life. The PWL of both carrots and tomatoes significantly increased with an
increase in storage temperature, arid the effect was higher for carrots than for tomatoes
during storage. The skin and epidermis tissue of tomatoes seemed to be highly resistant
to moisture transfer. Because carrots do not have that protection, excessive dehydration
and consequent shrinking was the most serious problem associated with carrots stored at
room temperature. This confirms that air RH is more crucial for carrots than for
tomatoes during storage. The interaction between pre- and postharvest treatments and
storage temperature had a significant effect on the PWL, although this interactive effect
affected carrot moisture loss more than that of tomatoes. As a general trend, the TAC
decreased faster in carrots stored at room temperature, due to a higher rate of hydrolysis
of polysaccharides to free sugars, and high utilization of these sugars in the. glycolysis
process. Similarly, the free sugars decreased faster in tomatoes stored at room
temperature than at 13°C.
Storage temperature was shown to be the most important factor that affects the
microbiological flora. Room temperature generally allowed significantly greater growth
of total aerobic bacteria, molds, yeasts and total coliforms, in both tomatoes and carrots,
than storage at lower temperatures. This study also showed that the lower optimum
storage temperatures, 1°C for carrots and 13°C for green mature tomatoes, maintained
the chemical, biochemical and biological qualities better, resulting in prolonged shelf
life with better marketability. At room temperature storage, ComCat® treated tomatoes
performed better in maintaining postharvest quality, compared to control tomatoes.
Regarding disinfecting treatments, the anolyte water was found to be as effective as
chlorinated water in reducing the microbial populations in carrots and tomatoes during
storage. A dipping time as short as 5 minutes in anolyte water was shown to be as
effective as 20 minutes in chlorinated water (Seyoum el al., 2002). It was noticed that
visible mold growth and decay was higher in carrots dipped in chlorinated water
towards the end of storage at room temperature, while the anolyte water treated carrots
232
General Discussion and Conclusions
showed no sign of visible mold development and decay. The effectiveness of
disinfecting treatment was maximized with MAP, and their coupled effect significantly
decreased the natural microbiological flora of tomatoes and carrots during storage. The
disinfecting treatment, when combined with MAP and optimum temperature storage of
carrots and tomatoes, further improved the microbiological quality. The statistical levels
of interactions between these postharvest treatments and storage time on shelf life and
quality improvement of carrots and tomatoes are shown in Appendix A.1.- A.4.
These disinfecting treatments also affected several quality parameters of tomatoes
and carrots. Carrots lost more moisture when treated with chlorine solution than with
anolyte and distilled water, at both low and high storage temperatures. A general trend
of higher chemical quality such as TSS, TAC, glucose, fructose and total soluble sugar
contents, were found in carrots dipped in anolyte water. This would imply that anolyte
water least affected the chemical quality of carrots, when compared to chlorinated
water, suggesting less influence on physiological and biochemical activities. However,
the ComCat® treated carrots dipped in chlorinated water, had slightly higher glucose
and fructose contents at the end of 28 days of storage. The higher concentrations of
these free sugars (glucose and fructose) in ComCat® treated carrots dipped in
chlorinated water could indicate higher rates of hydrolysis of the available
carbohydrates.
Gas concentrations were also affected by the disinfectants. The O2 concentrations
decreased slightly faster in packages of ripening tomatoes dipped in chlorinated water
than in packages of tomatoes treated with anolyte water. Similarly, the CO2
concentrations increased slightly faster in packages of ripening tomatoes treated with
chlorinated water, than those treated with anolyte water, especially during the early
active ripening periods. These results thus showed that chlorine treatment caused the
rate of respiration and metabolism of tomatoes to increase, which is not desirable for the
extension of shelf life. This effect on gas concentrations was greater for tomatoes than
for carrots. The PWL and concentrations of free sugars were slightly lower in tomatoes
233
General Discussion and Conclusions
dipped in anolyte water than in chlorinated water. After 30 days at room temperature
and 13oe, the TSS and AA content was significantly higher in tomatoes dipped in
anolyte water than in chlorinated water. This was because anolyte water decreased the
ripening and senescence processes of tomatoes, compared to chlorine disinfected ones.
Similarly, the PG and POX activities were slightly lower in tomatoes disinfected in
anolyte water, supporting the above-derived explanation of lower respiration and
metabolism rates. Anolyte water therefore resulted in a better marketability of tomatoes.
Sprouting of carrots was inhibited more by chlorine solution than by anolyte water
during storage at room temperature. Anolyte water treated carrots started sprouting after
1 week during storage at ambient conditions. Although sprouting is not a desirable
quality during storage, carrots dipped in anolyte water seemed to have normal
physiological activities, such as respiration and metabolic activities, and therefore will
sprout. It therefore seems as if the normal physiological state of carrots at harvest were
not affected by anolyte water, compared to that of carrots dipped in chlorinated water.
These differences in metabolic activity were not clearly noticeable in the case of
tomatoes that were disinfected in chlorinated or anolyte water and stored at room
temperature. The reason for this could be that the skin and epidermis of tomatoes
seemed not to be permeable to external materials such as chlorine, and therefore protect
the tissue from damage. Carrots have absorbing tissue, while tomato epidermis, and the
outer wall of the pericarp tissue, is more resistant to diffusion of exogenous material to
the internal parts. This could be the reason why the surface skin and tissue of carrots
showed signs of etching by the chlorine solution. The subsequent effect of this damage
on storage quality was more evident at room temperature storage. Thus, anolyte water
dipping treatment, when combined with optimum storage temperature, improves the
shelf life of carrots.
These results therefore provide evidence that anolyte water disinfecting of vegetables
is not just equal to that of chlorinated water, as the microbiological analyses indicate,
but even better, as derived from the chemical and biochemical analyses.
234
General Discussion and Conclusions
The main aim of this study was the integration of preharvest ComCat® treatment
with postharvest quality changes of carrots and tomatoes. The preharvest ComCat®
treated carrots and tomatoes were investigated on a wide variety of variables. The TAC,
glucose and fructose content, SH ratio, and population of total aerobic bacteria of
carrots during storage, were significantly affected by the preharvest ComCat® treatment.
This is confirmed by the work of Nilsson (1987), who reported that the growing
conditions of carrots influenced the sucrose content in the roots. The ComCat®
treatment had no significant effect on the concentrations of gases, PWL, TSS, sucrose
content, populations of yeasts, molds and coliforms in carrots during storage. As a
general trend, the free sugar contents seemed to be lower in ComCat® treated carrots
during storage. The reason for this could be a higher metabolism rate, due to increased
utilization of sugar for normal respiration and metabolism, or lower hydrolysis of
carbohydrates to sucrose, glucose and fructose. Apart from sucrose content, the free
sugars remained lower in ComCat® treated tomatoes, although differences were not
significantly different from the controls. It also seemed as if the sucrose contents of
tomatoes were more sensitive to ComCat® treatment, when compared to the hexose
sugars. The calculated sucrose equivalent was not significantly affected by ComCat®
treatment and should therefore also not affect the sweetness. The TSS, hexose content
and PG activity in tomatoes during storage were not significantly affected by the
ComCat® treatment. The two-way interaction between ComCat® treatment and
disinfecting + MAP treatments had a significant influence on the sucrose and fructose
content, SH ratio, and population of total aerobic bacteria of carrots during storage.
Likewise, the two-way interaction between the ComCat® treatment and storage
temperature had a significant effect on PWL, TSS, TAC, fructose content, and
populations of total aerobic bacteria, and moulds and yeasts. The PWL, populations of
aerobic bacteria, moulds and yeasts, and coli forms were significantly influenced by the
three-way interaction between the pre- and postharvest treatments. In general, the data
showed the existence of strong relationships between the ComCat® treatment, and
quality changes of carrots during storage. The high fresh harvest yield of ComCat®
235
General Discussion and Conclusions
treated carrots can be best maintained by subjecting to disinfecting, MAP and low
temperature storage. The statistical levels of interactions between these pre- and
postharvest treatments, and storage time on shelf life and quality improvement of
carrots and tomatoes are shown in Appendix A.l.- AA.
In chapter 4 the effect of preharvest ComCat® treatment on the postharvest quality of
tomatoes was explored. In this study, several advantages of ComCat® treatment on the
storage of tomatoes were identified. ComCat® treatment had a significant effect on
several parameters including PWL, pH, sucrose content, AA content, POX activity,
total aerobic bacteria, molds and yeasts, total coliforms and marketability. The low pH,
high TTA, low concentrations of free sugars and high POX activity in green mature
tomatoes at harvest, could be responsible for better microbiological quality of ComCat®
treated tomatoes. It is known that pathogenesis resistant proteins, such as POX, are
antimicrobial enzymes, since these enzymes protect cell walls from microbial infection
(Khripach et al. 1997; Schnabl et al., 2001).
At room temperature storage, ComCat® treated tomatoes performed better than
control tomatoes. ComCat® treatment significantly reduced the rates of consumption of
O2 and liberation of C02 in packaged tomatoes stored at room temperature. These
suggest lower respiration rates, compared to the controls. Further benefits of ComCat®
treatment on the shelf life of tomatoes at room temperature include better chemical
quality in terms of higher TSS content, lower pH and higher TTA, accumulation of
fructose towards the end of storage, higher total soluble sugar and sugar-acid ratio,
better microbiological quality and marketability.
The effect of ComCat® treatment on the postharvest quality of vegetables seemed to
vary with the type of produce. The preharvest ComCat® treatment had a significant
effect on the O2 and N2 concentrations in packages of tomatoes, while it had no
significant effect on the gas concentrations in packages of carrots during storage. None
of the interactions between the preharvest ComCat® and postharvest treatments had a
significant influence on the concentrations of O2, CO2 and N2 in packages of carrots
236
General Discussion and Conclusions
during storage. However, the CO2, 02, and N2 concentrations In the headspace of
tomato packages were highly affected due to the interactive effect of pre- and
postharvest treatments. These results therefore support the findings that preharvest
ComCat® treatment affected the respiration and metabolism of tomatoes more than that
of carrots.
The interactive effect of pre- and postharvest treatments had a significant influence
on the changes in TSS of tomatoes during storage, while only the interaction between
ComCat® treatment and storage temperature had an effect on changes in TSS of carrots.
This analysis therefore implied that ComCat® treatment, when combined with
postharvest treatments, seemed to have a greater influence on the changes in TSS of
tomatoes than on carrots. The sugar turnover was also differently affected by ComCat®
treatment in stored carrots and tomatoes. The changes in sucrose content of carrots, as
well as tomatoes, was influenced by the ComCat® treatment, while TAC, glucose and
fructose content and SH ratio was only affected in carrots. The interactive effect of
ComCat® treatment and storage temperature on the changes in free sugars and total
soluble sugar affected tomatoes more than carrots. AA content and POX activity was
only affected in ComCat® treated tomatoes.
At harvest, the natural microbial flora were lower in both ComCat® treated
vegetables studied. During the early storage period, the populations of microorganisms
in tomatoes were significantly decreased with the ComCat® treatment, compared to the
numbers of microorganisms in control tomatoes, while the microorganisms were not
significantly affected with the ComCat® treatment alone in carrots. The interactive
effect of ComCat® treatment and storage temperature was higher on the changes in
microbiological population in tomatoes than in carrots during storage. The reason for
this could have been due to the effect of ComCat® treatment on the TSS, sucrose,
glucose, fructose and total soluble sugar contents and POX activity observed in
tomatoes. This is in agreement with the view of Brackett (1987 and 1990) that the type
and population of natural microbiological flora of fresh produces could be dependent on
237
General Discussion and Conclusions
the chemical content of fruits and vegetables. It could also be possible that ComCat®
treated tomatoes and carrots have tissue that is more resistant to microbial growth than
the controls.
In summary, it seemed as if the ComCat® treatment had a higher significant effect on
the changes of the postharvest quality of the fruit part of the plant, or the vegetable
above ground, compared to the root part of the plant, or subsurface vegetable. Although
the keeping quality of ComCat® treated carrots and tomatoes were not markedly
different from the qualities of control vegetables when stored at the recommended
optimal temperatures, the postharvest quality was distinctly different. However, at room
temperature storage, ComCat® treated vegetables did not only display distinctively
better qualities, but also showed improved shelf life and better marketability.
The superior storage quality of ComCat® treated carrots and tomatoes encouraged
further investigations on the potential use of low-cost evaporative cooling, where
relatively lower temperatures and higher relative humidities could be maintained,
compared to ambient conditions. This part of the research was conducted in Ethiopia.
In chapter 5 and 6 the shelf life of CorrrCat'" treated and control carrots and tomatoes
stored under evaporative cooling conditions was investigated, for the potential
application to reduce postharvest losses of. A forced ventilation experimental EC unit
was developed for use in dry and hot conditions. The evaporative cooling reduced the
temperature by about lOoC (average) from the day temperature (25.0 - 36.0°C) to 16 -
25°C, with a rise in relative humidity of more than 38% above that of ambient air. The
advantages of this unit were, that temperature and relative humidity could be maintained
within limits during storage, to protect vegetables from environmental conditions,
resulting in increased shelf life.
Due to very high ambient air temperature and very low relative humidity, it was not
possible to store carrots and tomatoes even for 1 week in the study site at Alemaya,
Ethiopia. A rapid moisture loss in unpackaged carrots lead to the excessive dehydration
of within 5 days of storage at ambient temperature, while the ripening process was
238
General Discussion and Conclusions
hastened in unpackaged tomatoes, which was immediately followed by the collapse of
tissue. This then created conditions favourable for microbial proliferation and
progression of decay. MAP, with microperforated Xtend® film, significantly reduced
the PWL and juice content of carrots and tomatoes stored in EC and at ambient
temperature, delaying the senescence process, and improved the marketability of carrots
and tomatoes.
The quality of the ComCat® treated carrots and tomatoes stored in EC remained as
good as the quality of the untreated controls. However, the PWL, moisture loss, and loss
of juice content of carrots were slightly lower in ComCat® treated carrots than in control
carrots, confirming the previous data on these parameters (Chapter 3 and 4). At harvest,
ComCat® treated green mature tomatoes contained lower TSS, reducing sugar, non-
reducing sugar, total sugar and total aerobic bacteria. The TSS, reducing sugar, non-
reducing sugar and total sugars remained higher in ComCat® treated tomatoes during
storage in the EC. These results also confirmed that ComCat® treated tomatoes seemed
to have a better keeping quality when stored under evaporative cooling conditions,
which was slightly higher than the optimum storage temperature of 13°C. Although a
slight effect on microbial populations was observed, the difference between the
microbiological flora of ComCat® treated and control carrots and tomatoes was not
clear, due to the higher storage temperature as well as higher relative humidity in the EC
unit.
Despite the relatively higher minimum temperature levels, that can be achieved by
the EC, no sign of sprouting of the carrots was noticed during the 3 weeks of storage in
the evaporative cooling chamber.
These results therefore showed that the integration of pre- and postharvest practices
IS important to increase the potential benefits that can be gained from preharvest
treatments. The statistical levels of interactions between these pre- and postharvest
treatments and storage time on shelf life and quality improvement of carrots and
tomatoes are shown in Appendix A.l.- AA.
239
General Discussion and Conclusions
Future Research
Further research on the effect of ComCat® treatment and anolyte water treatment on
other fresh vegetables and minimally processed "fresh-like" vegetables should be
carried out. The integrated pre- and postharvest treatment approaches, to improve
productivity as well as storage performance, used in these studies, should be extended to
other fresh fruits and vegetables. The most resistant types of natural microorganisms of
vegetables to anolyte water disinfecting treatment should be identified. Regarding EC, a
multi-stage-cooling pad should be developed in order to reduce the storage temperature
down to a minimum temperature possible. Practical applications for EC units, e.g. in
markets, should be investigated. More work will be necessary on combining MAP in
nested packaging systems with EC in order to look at the interactive effect on biological
and biochemical changes of stored vegetables.
240
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274
SUMMARY
The improvement of the shelf life of carrots and tomatoes through integrated pre- and
postharvest treatments was investigated. Preharvest ComCat® treatment of carrot and
tomato plants was combined with postharvest disinfecting using chlorinated or anolyte
water, modified atmosphere packaging in Xtend® film, and different storage temperatures.
The physiological, chemical, biochemical and microbiological quality of carrots and
tomatoes were effectively improved by the combined effect of modified atmosphere
packaging in Xtend® film and the optimum storage temperatures of carrots, at 1°C, and
tomatoes, at 13°C. The shelf life of carrots and tomatoes was effectively improved, while
the quality characteristics were maintained.
Disinfecting vegetables with anolyte water gave better results than chlorinated water.
Chlorinated water treatment decreased ascorbic acid content, and increased physiological
weight loss and peroxidase activity. The surface tissue of carrots was etched by chlorine,
which created penetration zones for microorganism, and disadvantaged the shelf life.
Disinfecting with anolyte water, in combination with modified atmosphere packaging and
optimum storage temperatures, supported quality characteristics, and therefore contributed
to improving shelf life of carrots and tomatoes.
Preharvest spraying of plants with CorrrCat", improved the quality of carrots. At harvest
a slightly higher ascorbic acid, total soluble solids, total available carbohydrates and
sucrose content was noted. The sucrose to hexose ratio at harvest was also slightly higher,
and the microbial populations were slightly lower. Preharvest CorrrCat" treated tomatoes
275
Summary
had a lower pH, fructose and glucose content, and higher titratabie acidity and peroxidase
activity at harvest, which resulted in lower populations of natural microorganisms.
During storage at t3°C and room temperature, ComCat® treated tomatoes displayed
better maintenance of total soluble solids and ascorbic acid, and lower peroxidase activity.
These tomatoes also maintained better microbiological and marketable quality. The free
sugar content remained lower in ComCat® treated tomatoes as well as carrots during
storage. It seems as if the fruit part of a plant is more affected by the ComCat® treatment,
e.g. tomato, than the root part, e.g. carrots.
The interactive effect of preharvest ComCat® spraying, disinfecting with chlorinated or
anolyte water, modified atmosphere packaging in Xtend® film and different storage
temperatures was significant on several postharvest quality parameters of carrots and
tomatoes. The postharvest quality 'of ComCat® treated carrots and tomatoes in the storage
atmosphere, created by forced ventilation evaporative cooling, was also better than that of
the controls.
276
OPSOMMING
Die verebetering van rakleeftyd van geelwortels en tamaties gedurende ge-ïntegreerde
voor- en na-oes behandelings is ondersoek. Voor-oes ComCat® behandeling van
geelwortel- en tamatieplantjies is gekombineer met na-oes ontsmetting met gechlorineerde
of anolyte water, gemodifieerde atmosfeer verpakking met Xtend" film en verskillende
bergi ngstemperature .
Die fisiologiese, chemiese, biochemiese en mikrobiologiese gehalte van geelwortels en
tamaties is effektief verbeter deur die gekombineerde effek van gemodifieerde atmosfeer
verpakking in Xtend® film en optimum bergingstemperature van geelwortels, by 1°C, en
tamaties, by 13°C. Die rakleeftyd van geelwortels en tamaties is effektief verbeter terwyl
die gehalte-eienskappe behou is.
Ontsmetting van groente met anolyte water het beter resultate gelewer as met
gechlorineerde water. Gechlorineerde water behandeling het askorbiensuurinhoud verlaag,
en fisiologiese massaverlies en peroksidase aktiwiteit verhoog. Die oppervlakweefsel van
geelwortels is deur chloor geëts, wat indringingsones vir mikroorganismes geskep het, en
die rakleeftyd benadeel het. Ontsmetting met anolyte water, in kombinasie met
gemodifieerde atmosfeer verpakking en optimum bergingstemperature, het gehalte-
eienskappe ondersteun, en so bygedra tot verbetering van rakleeftyd van geelwortels en
tamaties.
Voor-oes bespuiting van plantjies met ComCat®, het die gehalte van geelwortels
verbeter. Tydens oes is 'n effens hoër askorbiensuur-, totale oplosbare soliede-, totale
277
Opsomming
beskikbare koolhidrate- en sukrose inhoud waargeneem. Die sukrose tot heksose
verhouding was ook effens hoër, en die mikrobiese populasies was effens laer. Voor-oes
ComCat® behandelde tamaties het by oes 'n laer pH, fructose- en glukose inhoud, en hoër
titreerbare suur en peroksidase aktiwiteit gehad, wat tot laer populasies mikroorganismes
gelei het.
Gedumede berging by l3°C en kamertemperatuur, het ComCat® behandelde tamaties 'n
beter behoud van totale oplosbare soliede en askorbiensuur, en laer peroksidase aktiwiteit
getoon. Hierdie tamaties het ook beter mikrobiologiese- en bemarkbare kwaliteit behou.
Die vrye suikerinhoud het laer gebly in ComCat® behandelde geelwortels sowel as tamaties
gedurende berging. Dit blyk dat die vruggedeelte van 'n plant, bv tamatie, meer deur die
ComCat® behandeling beïnvloed word as die wortelgedeelte, bv geelwortel.
Die interaktiewe effek van voor-oes ComCat® bespuiting, na-oes ontsmetting met
gechlorineerde- of anolyte water, gemodifieerde atmosfeer verpakking met Xtend® film en
verskillende bergingstemperature was beduidend op verskeie na-oes gehalteparameters van
geelwortels en tamaties. Die na-oes gehalte van ComCat® behandelde geelwortels en
tamaties in die bergingsatmosfeer, geskep deur forseerde ventilasie verdampingsverkoeling,
was ook beter as die van die kontroles.
278
.Appendix A
Appendix A.I. Analysis of variance for the effects of storage time and the interactive effects of storage time with pre- and postharvest treatments on the
qualities of tomatoes during storage at l3°C and room temperature (RT) for 30 days.
Treat- Postharvest gualiti' Qarameters
ment 02 CO2 N2 TSS PWL pH Sue, Glue. Fruc. TSug SE S/H TTA SlA AA TAB TF TC Mar.
0 *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
AD NS *** NS *** NS * ** NS ** * ** *** * *** *** ** NS *** NS
BD ** NS * *** NS ** NS NS NS NS NS NS ** *** *** *** *** *** ***
ABO NS NS NS *** *** * * NS NS NS NS NS * NS *** ** NS NS NS
CD *** NS *** *** NS *** ** NS ** NS * NS *** ** *** *** *** *** ***
ACD NS ** NS *** NS ** NS NS NS NS NS NS ** * *** ** NS NS **
N
-....J
'-D BCD * NS NS *** NS *** NS NS NS NS NS NS *** *** *** *** *** * ***
ABCD NS * NS *** NS ** NS NS NS NS NS NS ** *** *** *** NS NS NS
D = Storage time Sue, = Sucrose AA = Ascorbic acid
A = Preharvest treatment Glue, = Glucose TAB = Total aerobic bacteria
B = Disinfecting + MAP Fruc. = Fructose TF = Total molds and yeasts
C = Storage temperature Tsug. = Total soluble sugar TC = Total coliform bacteria
PWL = Physiological weight loss SE = Sucrose equivalent Mark. = Marketability
TSS = Total soluble solid S/H = Sucrose to hexose ratio
TTA = Titratabie aciditi' SIA = Sucrose to acid ratio
NS, *,**,*** Nonsignificant or significant at P~ 0.05,0.01 or 0.001 respectively.
Appendix A
Appendix A.2. Analysis of variance for the effects of storage time and the interactive effects of storage time with pre- and postharvest treatments on the
qualities of carrot during storage at 1°C and room temperature (RT) for 28 days.
Treatment Postharvest gualit;r Qarameters
02 CO2 N2 TSS PWL TAC Sue, Gluc. Fruc. Tsug S/H AA POX TAB TF TC
0 NS NS NS *** *** *** *** *** *** *** *** *** *** *** *** ***
AD NS NS NS NS *** *** * *** *** * ** NS NS NS *** NS
BD NS * * *** *** NS *** * ** * NS NS NS *** *** ***
ABO NS NS NS NS *** NS NS * * NS * NS NS ** NS NS
CD NS *** NS *** *** *** *** *** *** *** * *** *** *** *** ***
ACD NS NS * * NS * * NS * NS NS NS NS * NS NS
tv
00
0 BCD * *** NS * *** NS NS NS NS NS NS NS NS *** *** ***
ABCD NS NS NS NS *** NS * NS NS NS NS NS NS *** NS ***
D = Storage time Sue. = Sucrose AA = Ascorbic acid
A = Preharvest treatment Glue, = Glucose POX = Peroxidase activity
B = Disinfecting + MAP Fruc. = Fructose TAB = Total aerobic bacteria
C = Storage temperature Tsug. = Total soluble sugar TF = Total maids and yeasts
PWL = Physiological weight loss TTA = Total available carbohydrates TC = Total coliform bacteria
TSS = Total soluble solid S/H = Sucrose to hexose ratio
NS, *,**,*** Nonsignificant or significant at P:::;0.05, 0.01 or 0.001 respectively.
Appendix A
Appendix A.3. Analysis of variance for the effects of storage time and the interactive effects of storage time with pre- and postharvest
treatments on the qualities of tomatoes during storage inside the evaporative cooling chamber and ambient temperature (RT).
Treatment Postharvest quality parameters
- ---
TSS PWL JC ~H TTA RS NRS Tsug TAB TF Mark
0 *** *** *** *** *** *** *** *** * ** ***
AD *** * NS NS *** *** *** * NS NS NS
BD NS NS NS *** NS NS NS NS *** *** *
ABO NS NS NS * NS ** NS *** NS NS NS
CD NS *** *** *** NS * ** ** *** NS ***
ACD NS NS NS ** NS NS NS NS NS NS NS
N
00 BCD NS * *** * NS NS NS * NS * **
ABCD NS NS NS *** NS * * NS NS NS *
o = Storage time RS = Reducing sugar JC = Juice content
A = Preharvest treatment NRS = Non-reducing sugar Mark = Percentage marketability
B = Disinfecting +MAP TS = Total sugar
C = Storage temperature TAB = Total aerobic bacteria
PWL = Physiological weight loss TF = Total molds and yeasts
TSS = Total soluble solid TTA = Titratable acidit~
NS, *,**,*** Nonsignificant or significant at P~ 0.05, 0.01 or 0.001 respectively.
Appendix A
Appendix A.4. Analysis of variance for the effects of storage time and the interactive effects of storage time with pre- and postharvest
treatments on the qualities of carrots during storage at ambient (RT) and inside the evaporative cooler.
Treatment Postharvest quality parameters
pH PWL TSS MC JC RS NRS TSUG TAB TF Mark
-------
0 *** *** *** *** *** *** *** *** *** *** ***
AD ** NS * NS NS *** * *** NS NS NS
BD * *** *** *** ** * *** *** *** *** ***
ABO ** NS NS NS NS NS * NS * NS NS
CD *** *** *** *** *** *** * *** NS *** ***
ACD NS NS NS NS NS NS NS NS * NS NS
N
00 BCD ** *** *** *** * * NS * NS * *
N
·ABCD ** * * NS NS * NS * NS NS NS
D = Storage time RS = Reducing sugar JC = Juice content
A = Preharvest treatment NRS = Non-reducing sugar MC = Moisture content
B = Disinfecting +MAP Tsug. = Total soluble sugar
C = Storage temperature TAB = Total aerobic bacteria
PWL = Physiological weight loss TF = Total molds and yeasts
ID TSS = Total soluble solid Mark = Percentage marketabilityNS, *,**,*** Nonsignificant or significant at P~ 0.05,0.01 or 0.001 respectively.
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