Antioxidant compounds from four Opuntia cactus pear fruit varieties

The antioxidant compounds in extracts from four cactus (Opuntia species) fruit varieties were investigated. Conjugated flavonoids (quercetin, kaempferol and isorhamnetin), ascorbic acid, and carotenoids were isolated from the extracts. Quercetin was the most abundant in all varieties [O. ficus-indica (green-skinned), O. lindheimeri (purple-skinned), O. streptacantha (red-skinned), and O. stricta var. stricta (yellow-skinned)] examined. Kaempferol was found in green-skinned, purple-skinned and red-skinned varieties and isorhamnetin in green-skinned and purple-skinned varieties. The red-skinned fruits contained the most ascorbic acid (815 μg/g fw) and the yellow-skinned fruits the most carotenoids (23.7 μg/g fw). The antioxidant activity of the fruit extracts was stronger in the purple-skinned than other varieties. This result was consistent with total flavonoid content of the purple-skinned fruits. Thus, antioxidant capacity of cactus fruits may be attributed to their flavonoid, ascorbic acid and carotenoid contents. The data indicate that cactus fruits are a rich source of natural antioxidants for foods.