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

[摘要] English: Cactus pear plants (Opuntia ficus-indica and Opuntia robusta) are edible plants that grow andthrive in the semi-arid area of the Free State, South Africa, yet are unknown food sources. Cactuspear 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 thenutritional and therapeutic properties of cladodes and mucilage verified its high potential forhuman consumption. The development of mucilage into a commercial nutraceutical foodproduct offers an opportunity to add value to the crop while providing a healthy product thatcould 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 interms of the amount of quality of mucilage. Thus, the most appropriate cultivar for optimalmucilage yield and quality from forty-two local cultivars had to be selected and cladodeharvesting time established.It was found that mucilage yield was not a consequence of cladode size or moisture content, butof cultivar and viscosity. Seven cultivars were selected that proved to have the lowest viscositywhile commercially viable in South Africa (O. ficus-indica cultivars namely Algerian, Meyers,Morado, Ficus-Indica, Gymno-Carpo, Tormentosa, Turpin). The eighth cultivar represented adifferent species (O. robusta Robusta). Further morphological and rheological investigationsrevealed that the dormant stage (dormant months) would be the optimal harvesting time, whilethe 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 cultivarsshowed non-Newtonian, pseudoplastic tendencies. Higher viscosity mucilage was timedependent, rheopectic and had yield stress tendencies. Fluctuations in temperature, pH,concentration and electrolytes influenced the mucilage viscosity that could affect producttexture.In the analyses of the native mucilage, lower pH during summer was correlated to highermucilage yields. The flow properties, water- and oil- related properties showed the high potentialof mucilage powders as commercial nutraceutical product. The chemical analysis of freeze-driedmucilage powders showed high fibre and minerals, yet low fat and carbohydrates. Although theprotein 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 concurredwith the lower pH (as a consequence of CAM) that in turn affected the mucilage viscosity andyield. Mucilage was successfully applied to food products and is recommended forcommercialization as a nutraceutical food product.In terms of cultivar selection, 'Robusta' had the highest contents of protein, total fats (beneficialfatty acids), starch, potassium and phosphorous, while 'Algerian' mucilage had the lowest energyand insoluble fibre, but highest calcium, iron and copper contents. 'Gymno-Carpo' had highlinoleic acid, magnesium and manganese and good fat ratios.It is recommended that cladodes be harvested in the summer months, directly after the fruit hadbeen harvested for optimal mucilage yield and quality. 'Robusta' emerged as the best cultivar forhigher 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 specificfood applications.

[发布机构] University of the Free State