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Flavonoids quercetin, myricetin, kaemferol and (+)-catechin as antioxidants in methyl linleate

Pekkarinen, S.S., Heinonen, I.M., Hopia, A.I.
Journal of the science of food and agriculture 1999 v.79 no.4 pp. 499-506
flavonoids, quercetin, catechin, rutoside, alpha-tocopherol, oxidation, linoleic acid, antioxidants, structure-activity relationships
The antioxidant effect of the flavonoids quercetin, myricetin, kaemferol, (+)-catechin and rutin on methyl linoleate oxidation was investigated. In addition, the synergistic effects of flavonoids and alpha-tocopherol were studied. Oxidation was monitored by conjugated diene measurement and by determining the formation of hydroperoxide isomers by HPLC. The antioxidant activity of flavonoids in non-polar methyl linoleate differ from that previously reported in water-containing systems, such as LDL and liposome systems. The activity of antioxidants (10-1000 micromolar) measured by hydroperoxide formation decreased in the order: myricetin > quercetin > alpha-tocopherol > (+)-catechin > kaemferol = rutin. The antioxidant activity of flavonoids increased as the number of phenolic hydroxyl groups increased. In addition to the number of hydroxyl groups, other structural features such as the 2,3 double bond in the C-ring and a glycoside moiety in the molecule had an effect on the antioxidant activity. Myricetin and rutin, especially had a synergistic effect with alpha-tocopherol. Myricetin, quercetin and rutin protected alpha-tocopherol from decomposition, myricetin being the most protective. The relative hydrogen-donating activity measured by the ration of cis,trans- to trans,trans-hydroperoxide isomers formed during oxidation decreased in the order: alpha-tocopherol > myricetin > quercetin. Hydroperoxide isomeric distribution of the samples containing kaemferol or rutin did not differ from the control. Thus, although alpha-tocopherol was the most effective hydrogen-donor, myricetin and quercetin were more effective antioxidants in inhibiting the hydroperoxide formation in methyl linoleate.