An ecological study of yeasts associated with fruits and vegetables
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Date
2001-01
Authors
Wolmarans, Johannes Barend Bodenstein
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
English: Currently, fruits and vegetables suffer significant losses from fungal diseases after
harvest. The use of synthetic fungicides which pose a risk to human health and the
environment, have resulted in an intensive search for safer control of postharvest diseases
by the use of microorganisms, particularly yeasts, occurring naturally on the surfaces of
fruits and vegetables.
An ecological survey was preformed on five different fruit and vegetable commodities to
determine the diversity of yeast species associated with these commodities and the cause
of spoilage at different temperatures.
A. THE INCIDENCE OF YEASTS ASSOCIA TED WITH FRUITS AND
VEGETABLES.
Different fruits and vegetables were surveyed to determine the diversity of yeasts and to
differentiate between yeasts found on the surface and inner layer of the different fruit and
vegetable commodities. Bacterial growth dominated on the surface of vegetables due to
factors such as higher water content, more neutral pH and close proximity to the soil
facilitating their growth.
Yeasts represented the major component of the microflora on the surface of fruits due to
a lower pH and higher carbohydrate content that encouraged their growth. The inner layer
of both fruits and vegetables yielded lower microbial counts. Schizosaccharomyces
pombe and Debaryomyces hansenii were the predominant species isolated on both fruits
and vegetables. Spoilage of fresh fruits usually results from the fermentative activity of
yeasts, but no such species were isolated during this study.
B. THE GROWTH AND SURVIVAL OF YEASTS IN FRUITS AND VEGETABLES
STORED AT DIFFERENT TEMPERATURES.
The growth and survival of yeasts were carried out at different temperatures over a 30-
day period to determine an epiphytic yeast population developing on the surfaces of fruits
and vegetables. The chemical and physical composition were monitored over a 30-day
period to determine if the changes in pH and organic acids contributed to the developing
yeast population on the surface of fruits and vegetables.
A total of 119 yeast strains were isolated from fruits and vegetables with bacteria
dominating on the surface of vegetables and yeasts on the surface of fruits. The most
predominating species isolated were S. pombe and D. hansenii. A new yeast species,
showing cellulase activity, was isolated from potatoes on day 20 at 25°C.
C. THE IDENTIFICATION OF A NEW BASIDIOMYCETOUS YEAST SPECIES
ISOLATED FROM POTATOES.
The new basidiomycetous related species showed interesting characteristics in
assimilating lactose as a carbon source. Its sexual reproduction by teliospores verifies the
characteristically difference compared to Cryptococcus and Rhodotorula spp. where no
sexual reproduction is noted. Accordingly, the new species was described.
Description
Keywords
Yeast fungi, Food spoilage, Food -- Microbiology, Dissertation (M.Sc. (Microbiology and Biochemistry))--University of the Free State, 2001