Antioxidant protective effect of flavonoids on linoleic acid peroxidation induced by copper(II)/ascorbic acid system

► Linoleic acid peroxidation was followed in Cu(II)/ascorbate/O2 containing solutions. ► The peroxidation inhibitive order of flavonoids was: morin > catechin ≥ quercetin. ► The possible prooxidative effects of catechin and quercetin were assessed. ► The results were evaluated in the light of structure-activity relationships. ► Cu chelation and redox potential were important in antioxidant/prooxidant activity.