Grapefruit (Citrus paradisi) extracts inhibited ascorbate-iron-induced lipid peroxidation of liver microsomes in a dose-dependent way, but were less effective antioxidant towards an NADH-iron induced system.46 Naringin (naringenin 7-ß-neohesperidoside) 8, a major component in grapefruit, was reported not to contribute to the lipid peroxidation but to be responsible for most of the hydroxyl radical scavenging activity of grapefruit. Grapefruit was also effective towards ascorbate-iron-induced lipid per-
oxidation of P450-containing microsomes.8 According to Wang et al.33 orange (Citrus sinensis) was more active than pink grapefruit in scavenging peroxyl radicals (ORAC assay) while grapefruit juice was more active than orange juice.
In a study by Scarlata and Ebeler61 citrus juices from orange, tangerine and grapefruit did not have any antioxidative effect towards oxidation on lipoproteins isolated after plasma spiking. In this study, hesperetin and hesperidin, two of the major phenolic compounds in citrus fruits, did not show any activity. On the contrary, Miller and Rice-Evans43 showed that in orange juice the total antioxidant activity could be accounted for by hesperidin 9 and narirutin 10. Bocco et al.62 studied the antioxidant effect of by-products of the citrus juice industry and found that, in general, the seeds of lemon, bergamot, sour orange, sweet orange, mandarin, pummelo and lime possessed greater antioxidative activity than the peels.
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