Comparative analyses of total phenols, antioxidant activity, and flavonol glycoside profile of cladode flours from different varieties of Opuntia spp

The phenolic, flavonoid, and antioxidant contents of methanol extracts of nine samples of Mexican cactus ( Opuntia spp.) cladodes processed into flours were studied. Opuntia undulata contained the highest amount of phenols 905.08 ± 64.51 μg of gallic acid equivalents (GAE)/g]. The oxygen radical absorbance capacity (ORAC) of the cladode flour extracts indicated that Opuntia robusta var. Gavia 738.8 ± 89.9 μmol of Trolox equivalents (TE)/g] contained the highest antioxidant capacity. ORAC values significantly correlated to total phenols but not to flavonoid contents and were comparable to cranberries and blackberries. Glycosidic forms of isorhamnetin and kaempferol were identified via high-performance liquid chromatography-photodiode array (HPLC-PDA) and HPLC-mass spectrometry (MS), with isorhamnetin being the most abundant flavonol in all samples, except for Opuntia lindheimeri . The effectiveness of acid hydrolysis varied among species because of the different flavonol profiles. For some varieties, the triglycosidic forms were partially acid-hydrolyzed, giving an increase in the content of diglycosides. Optimization of hydrolysis for each species is required to estimate the total amount of each flavonol.