Antioxidant activity of phenolic compounds in 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation:: Synergistic and antagonistic effects

Interactions between phenolic antioxidants in binary systems were determined by adding two antioxidants simultaneously in equimolar proportions to an aqueous dispersion of linoleic acid that was then subjected to 2,2'-azobis (2-amidino-propane) dihydrochloride-induced oxidation and by evaluating the protective effect of the antioxidant mixture. The antioxidant power of the mixture was then compared with the expected antioxidant activity calculated by the sum of efficiencies of each compound separately, relative to their proportions in the mixture. If it was higher, a synergy was pointed out whereas a lower value was representative of an antagonism. Thus, synergistic effects were observed between rosmarinic acid and quercetin, or rosmarinic acid and caffeic acid, whereas antagonistic effects were obtained with the following mixtures: alpha-tocopherol/caffeic acid; alpha-tocopherol/rosmarinic acid; (+)-catechin/caffeic acid; and caffeic acid/quercetin. These mixture effects are partly explained by regeneration mechanisms between antioxidants, depending on the chemical structure of molecules and on the possible formation of stable intermolecular complexes.