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The antioxidant activity of flavonoids in cell-free systems has been studied extensively. We compared flavonoids with different structural features on their abilities to protect live Caco-2 intestinal cells from lipid peroxidation due to hydrogen peroxide and Fe sup 2+ treatment. Flavonoids with o-dihydroxyl or vicinal-trihydroxyl groups, including quercetin, myricetin (flavonol), luteolin (flavone) and (-)-epigallocatechin gallate (EGCG; flavanol), when coincubated with a mixture of 30 [mu] mol/LH sub 2 O sub 2 and 30 [mu] mol/L FeSO sub 4, prevented the formation of malondialdehyde (MDA) at 1 or 10 [mu] mol/L in at least one of two separate experiments. In experiments in which flavonoids were preincubated with cells but removed before the 30 [mu] mol/LH sub 2 O sub 2 and Fe sup 2+ treatment, quercetin at 0.1 [mu] mol/L, EGCG at 1 [mu] mol/L and luteolin at 10 [mu] mol/L exerted protective effects in at least one of two …