Hydroxyl radical scavenging activity of flavonoids

Abstract The flavonoids scavenge hydroxyl ( . OH) radicals generated by UV photolysis of hydrogen peroxide. Free . OH radicals were spin-trapped by 5,5-dimethyl-1-pyrroline N -oxide and the adduct was detected by high pressure liquid chromatography coupled with an electrochemical detector. The scavenging activity of flavonoids decreases in the order: myricetin > quercetin > rhamnetin > morin > diosmetin > naringenin > apigenin > catechin >5,7- dihydroxy -3′,4′,5′-trimethoxyflavone > robinin > kaempferol > flavone. The activity increases with the number of hydroxyl groups substituted in the aromatic B-ring. The presence of a hydroxyl at C-3 and its glycosylation does not further increase scavenging efficiency. It is suggested that the overall antioxidant effect of flavonoids on lipid peroxidation may be due to their . OH and O· − 2 scavenging properties and the reaction with peroxy radicals.