Selection, extraction, characterization and application of mucilage from cactus pear (Opuntia ficus-indica and Opuntia robusta) cladodes

English: 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.