Antioxidant activity is widely used as a parameter to characterize different plant materials for potential health benefits. This activity is related with compounds capable of protecting a biological system against the harmful effect of reactions that can cause excessive oxidation, involving reactive oxygen and nitrogen species (RONS). There has been growing interest in the beneficial health effects of consuming fruits and vegetables. Mainly, the presence of lycopene, ascorbic acid, and phenolic antioxidants is believed to have the protective mechanism. The free radical-scavenging activities of grapefruit extract of `Rio Red', `Marsh White', and commercial juice were extracted with different solvents, such as hexane, ethyl acetate, and chloroform. The dried extracts were screened for their radical scavenging activity using the α,α -diphenyl-β-picrylhydrazyl (DPPH) method. The ethyl acetate extracts of commercial juice and `Marsh White' were found to possess more radical scavenging activity compared with the other two extracts. However, chloroform extracts of `Rio Red' grapefruit were the most active, which may be ascribed to the presence of more lycopene. Furthermore, the antioxidant capacity of `Rio Red' and `Marsh White' extracts was assayed through the phosphomolybdenum method and expressed as equivalent to ascorbic acid (μmol·g-1 of the extract). The order of antioxidant capacity for `Rio Red' extracts was found to be hexane > chloroform > ethyl acetate, while the order for `Marsh White' was chloroform > hexane > ethyl acetate. The results indicate that the extent of antioxidant activity of the extract is in accordance with the amount of lycopene/phenolics present in that extract; commercial juice and `Rio Red' may provide a good source of antioxidants.
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