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Browsing Consumer Science by Author "Du Toit, Alba"
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Item Open Access Antioxidant content and potential of fresh and processed cladodes and fruit from different coloured cactus pear (Opuntia ficus-indica and Opuntia robusta) cultivars(University of the Free State, 2013-02) Du Toit, Alba; De Wit, M.; Osthoff, G.English: Different coloured cactus fruit, peel, seeds and cladodes were studied for antioxidant content and -capacity in fresh products. Fruit and cladodes from seven different cultivars from the O.ficus-indica spp. and one of O. robusta spp. were collected representing the four colours of fruit available namely, green, pink, orange and purple. It was found that fresh cactus pear fruit and cladodes contained exceptionally high levels of Ascorbic acid, Total Phenolics and Betalains and modest amounts of Carotene. Antioxidant potential remained at very high levels regardless of the specific antioxidant content. The highest antioxidant content and -capacity were found in purple (O.robusta Robusta) fruit and cladodes, attributed to the high levels of Betalains. Ascorbic acid, working synergistically with Phenolics, was found to provide almost as much antioxidant capacity to orange fruit coloured cultivars. It was thus found that cultivars with purple and orange fruit and cladodes were the best in regards to antioxidant content as well as -potential. Five cultivars, representing the four colours were further investigated by processing into different products in order to determine the influence that preservation techniques had on the antioxidant content and potential in the fruit, peel and cladodes. Juice, dried products, chutneys, whole preserves and pickles were prepared from the fruit (pulp), peel and cladodes of the five different coloured cultivars that attained the highest values in the fresh study. Betalains were retained in processed products; Ascorbic acid was mostly preserved in the processed products that involved minimal heat treatments, while Carotene and Phenolics increased after processing. Processed cladodes, more than fresh cladodes, from all the cultivars, were concluded to provide an excellent source of antioxidants and could be suggested for products such as cladode flour and pickles. The peel in general was found to contain very similar antioxidant content and potential as the fruit and should be included in products when possible. In fruit, the purple fruit is highly recommended for processing, as it displayed the highest antioxidant potential in its fresh form and maintained these levels in processed product. Dried fruit is the product with the highest source of antioxidants to the consumer. Juice and chutney from pink or orange fruit would also provide products that the South African consumer is accustomed to with exceptionally high antioxidant potential. The study brings to light the potential that cactus pear products have for the food industry. It could be developed into a profitable industry if the public could be made aware of the health benefits that they provide.Item Open Access Selection, extraction, characterization and application of mucilage from cactus pear (Opuntia ficus-indica and Opuntia robusta) cladodes(University of the Free State, 2016-08) Du Toit, Alba; De Wit, Maryna; Hugo, Arno; Fouché, HermanEnglish: Cactus pear plants (Opuntia ficus-indica and Opuntia robusta) are edible plants that grow and thrive in the semi-arid area of the Free State, South Africa, yet are unknown food sources. Cactus pear cladodes could be developed into a crop that could offer solutions in terms of food security, yet are ignored and underutilized in South Africa. Extensive research done abroad on the nutritional and therapeutic properties of cladodes and mucilage verified its high potential for human consumption. The development of mucilage into a commercial nutraceutical food product offers an opportunity to add value to the crop while providing a healthy product that could significantly enhance the well-being of the South African consumer. A successful, easy, inexpensive and chemical free extraction process was developed, yet cladodes were not equal in terms of the amount of quality of mucilage. Thus, the most appropriate cultivar for optimal mucilage yield and quality from forty-two local cultivars had to be selected and cladode harvesting time established. It was found that mucilage yield was not a consequence of cladode size or moisture content, but of cultivar and viscosity. Seven cultivars were selected that proved to have the lowest viscosity while commercially viable in South Africa (O. ficus-indica cultivars namely Algerian, Meyers, Morado, Ficus-Indica, Gymno-Carpo, Tormentosa, Turpin). The eighth cultivar represented a different species (O. robusta Robusta). Further morphological and rheological investigations revealed that the dormant stage (dormant months) would be the optimal harvesting time, while the selection of cultivars were narrowed down to four (O. ficus-indica Algerian, Morado, Gymno- Carpo and O. robusta Robusta). Mucilage (native and freeze-dried powders) from all cultivars showed non-Newtonian, pseudoplastic tendencies. Higher viscosity mucilage was time dependent, rheopectic and had yield stress tendencies. Fluctuations in temperature, pH, concentration and electrolytes influenced the mucilage viscosity that could affect product texture. In the analyses of the native mucilage, lower pH during summer was correlated to higher mucilage yields. The flow properties, water- and oil- related properties showed the high potential of mucilage powders as commercial nutraceutical product. The chemical analysis of freeze-dried mucilage powders showed high fibre and minerals, yet low fat and carbohydrates. Although the protein content was low, the presence of proteins was confirmed for the protein-lipid interaction necessary in the stabilization action of emulsions. The higher organic acids in summer concurred with the lower pH (as a consequence of CAM) that in turn affected the mucilage viscosity and yield. Mucilage was successfully applied to food products and is recommended for commercialization as a nutraceutical food product. In terms of cultivar selection, ‘Robusta’ had the highest contents of protein, total fats (beneficial fatty acids), starch, potassium and phosphorous, while ‘Algerian’ mucilage had the lowest energy and insoluble fibre, but highest calcium, iron and copper contents. ‘Gymno-Carpo’ had high linoleic acid, magnesium and manganese and good fat ratios. It is recommended that cladodes be harvested in the summer months, directly after the fruit had been harvested for optimal mucilage yield and quality. ‘Robusta’ emerged as the best cultivar for higher viscosity mucilage and Algerian for lower viscosity mucilage of the best quality. However, a careful selection of the most appropriate cultivar mucilage would be paramount for specific food applications.