The morphological, physiological, physico-chemical evaluation and sensory profiling of Nopalitos from 20 South African cactus pear cultivars
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Date
2020
Authors
Makhalemele, Bonolo Lulu
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
The exponential increase of food insecurity around the world warrants for the development of mitigation strategies which include looking for new food sources that will not only minimise the effects of food insecurity but are also sustainable. The cactus Opuntia produces edible stems (cladodes) and fruits with high nutritional value in terms of minerals, protein, dietary fibre and phytochemicals, and with the increase in the global shift towards the use of natural plant materials in various industries including food, cosmetics as well as pharmaceuticals, the cactus pear plant makes for great interest. In addition to its multifaceted properties, the plant is appealing all the more in the South African landscape because of its high ecological adaptivity, with most of its species being able to survive in arid and semi-arid places. As such, a comprehensive study on the young edible stems (nopalitos) from twenty South African
cactus pear cultivars was conducted because they are the one part of the cactus plant that is underutilised and consequently almost exclusively used for animal feed.
Nopalitos from the twenty South African cultivars were harvested and various morphological, physiological, physico-chemical and chemical tests were conducted over 2 years (2018 and 2019). These tests included the weight, moisture content, solids, sugar content, acidity, colour, mucilage content and viscosity thereof, and pH which are some of the main factors which affect the palatability and overall functionality of the vegetable. Further investigations included
the nutritional content of the stems as well as the sensorial attributes to determine the overall eating quality and acceptability of the stems.
Upon concluding the various experiments, interesting trends were noticed between the two years with the 2018 harvest having produced more favourable attributes than the 2019 harvest. The 2018 harvest produced nopalitos which were thinner and greener stems which had the least mucilage content and viscosity while presenting high values of solids and sugar. These attributes are important as they affect the taste, keeping qualities and overall acceptability of the samples the most.
When comparing the effects of cultivar, year of harvest and the effects of cultivar and year of harvest interaction on the various nopalito attributes, it was observed that the effect of cultivar on the various parameters had the most significant differences. These significant differences were found in the weight (g), length (cm), width (cm), diameter (cm), pulp (before centrifuge) (g), extracted mucilage (g), waste (g), % mucilage yield, firmness (mm), titratable acidity expressed as % citric acid, line-spread (cm) method of determining viscosity, sugar (TSS °Brix) content as well as the colour coordinates of the various nopalito cultivars (L*, a*, b*, Chroma (Saturation Index) and hue angle). The best overall cultivars following this investigation were Meyers, Malta, Nudosa, Fusicaulis, Fresno and Morado.
Sensory profiling of the nopalitos from twenty South African cactus pear cultivars aimed to determine consumer acceptability showed interesting variations. The cultivars were easily comparable with green pepper and cucumber in certain aspects. Among the twenty nopalito cultivars, Skinners Court, Turpin, Fusicaulis, R1251 and Rossa were ‘neither liked nor disliked’ by the consumers, as they were all ranked higher than the other cultivars, while Robusta was the least liked cultivar.
Nutritional analyses were conducted for the six nopalito cultivars which were deemed to be the overall best following the morphological and physico-chemical analyses as well as the consideration of the sensorial properties of the different cultivars. From this investigation, Malta, Fusicaulis and Meyers were deemed as the best cultivars out of the six as they presented the highest nutritional content.
Overall, the reported work has shown the high quality of the nopalitos as a vegetable source which is easily and competitively compared to other known vegetables/crops such as green pepper and cucumber in terms of sensorial properties and oranges, soybeans and other nopalito cultivars found in various parts of the world in terms of nutritional, morphological and physico-chemical properties.
It is recommended that future research into the nopalitos include ways in which the stems can be prepared and incorporated into different products to increase the overall acceptability of South African consumers.
Description
Dissertation (M.Sc.(Food Science))--University of the Free State, 2020
Keywords
Food security, Opuntia ficus-indica, cactus pear, nopalitos, cultivar, morphological properties, physico-chemical properties, nutritional content, Check-All-That-Apply, consumer acceptability, South Africa