EFFECT OF MICROWAVE PRETREATMENT ON BIOACTIVE COMPOUNDS EXTRACTION FROM XOCONOSTLE (Opuntia joconostle) BY-PRODUCTS

Xoconostle is a common feature of the Mexican landscape in semi-arid regions. Its mesocarp is processed into jellies, sauces and other products but the endocarp is discarded as waste; in spite of containing appreciable amounts of bioactive compounds with antioxidant activity. This study aimed to evaluate the effect of microwave pretreatment on the extraction of phenolic and flavonoids compounds from xoconostle's endocarp and to determine their antioxidant capacity and microstructural changes. According to the surface response methodology applied, the optimum conditions for phenolic compounds and flavonoid extraction from endocarp using microwave pre-treatment (297 W for 5.5 min) were: 0% ethanol, 5 degrees C and 10 min of stirring. The total phenolic, total flavonoid, betalains and ascorbic acid contents, as well as the antioxidant capacity were higher in the microwave pretreated samples compared with non-pretreated ones. The following phenolic acids and flavonoids were identified in the endocarp extracts obtained under optimal conditions: gallic, caffeic. protocatechuic, coumaric and, vanillic acids, epicatechin and catechin. Our results suggested that the application of a microwave pretreatment improves compounds extraction in xoconostle's endocarp, which could be an alternative source of bioactive substances with high antioxidant capacity.