Metabolite profiling of three Opuntia ficus-indica fruit cultivars using UPLC-QTOF-MS in relation to their antioxidant potential

Abstract

Opuntia ficus-indica is the economically important cactus species belonging to the Cactaceae family. Its importance arises from its nutritional value and various biological activities such as antioxidant, anticancer and antimicrobial activities. This study attempts to characterize the metabolic profile of three O. ficus cultivars having different colors, i.e., red ‘Rose’, greenish white ‘Bianca’ and yellow-orange represented by peels and pulp tissues using ultra-performance liquid chromatography coupled to high resolution time of flight mass spectrometry (UPLC-QTOF-MS). A total of 45 metabolites were identified mainly flavonoids: isorhamnetin conjugates and phenolic acids, whereas betaxanthins and coumarins were present at lower levels. Principle component analysis and orthogonal projection discriminant analysis showed that dihydroxy psoralen-O-hexoside and glycosidic conjugates of ferulic acid were the most discriminatory metabolites among the peels and pulps within the different cultivars. On the other hand, the level of flavonoids was comparable among the cultivars. The antioxidant activity of peels and pulps extracts were further measured using 2,2-diphenyl-1-picrylhydrazyl and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) assays. ‘‘Rose’’ cultivar peel rich in dihydroxy psoralen-O-hexoside showed the highest antioxidant activity in both assays. This suggested that coumarins and flavonoids mediated high antioxidant activity of O. ficus-indica fruits although present at low levels