Antioxidant activity of flavonol aglycones and their glycosides in methyl linoleate

The antioxidant activities of the flavonol aglycones, quercetin and myricetin, and their selected glycosides were compared in bulk methyl linoleate oxidized at 40°C. Methyl linoleate hydroperoxide formation, hydroperoxide isomer distribution, and ketodiene formation were followed by using high‐performance liquid chromatography (HPLC) analysis. The aglycones, quercetin and myricetin, were consistently more active in bulk methyl linoleate than their glycosides and more active than α‐tocopherol at 500 and 1000 µM. At 50 µM, the order of activity was myricetin > α‐tocopherol > quercetin, and the order of activity of quercetin and its derivatives was quercetin > quercitrin > isoquercitrin > rutin. Myricitrin was slightly less active than myricetin. The sugar moiety was shown to have a marked effect on the antioxidant activity of flavonols. The rhamnoside derivatives, quercitrin and myricitrin, both possessed activity close to that of their corresponding aglycones. The different activities of glycosides could be partly explained by different solubilities and by differences in oxidizability of glycosides containing a monosaccharide or disaccharide at the C3 position. The effect on hydroperoxide isomer distribution indicates that α‐tocopherol was a more effective hydrogen donor than flavonoids, although flavonoids were more effective in inhibiting oxidation of methyl linoleate.