Antioxidant activity of flavonol aglycones and their glycosides in methyl linoleate

The antioxidant activities of the flavonol aglycones, quercetin and myricet in, and their selected glycosides were compared in bulk methyl linoleate ox idized at 40 degrees C. Methyl linoleate hydroperoxide formation, hydropero xide isomer distribution, and ketodiene formation were followed by using hi gh-performance liquid chromatography (HPLC) analysis. The aglycones, querce tin and myricetin, were consistently more active in bulk methyl linoleate t han their glycosides and more active than alpha-tocopherol at 500 and 1000 mu M. At 50 mu M, the order of activity was myricetin > alpha-tocopherol > quercetin, and the order of activity of quercetin and its derivatives was q uercetin > 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, querc itrin and myricitrin, both possessed activity close to that of their corres ponding aglycones. The different activities of glycosides could be partly e xplained by different solubilities and by differences in oxidizability of g lycosides containing a monosaccharide or disaccharide at the C-3 position. The effect on hydroperoxide isomer distribution indicates that alpha-tocoph erol was a more effective hydrogen donor than flavonoids, although flavonoi ds were more effective in inhibiting oxidation of methyl linoleate.