Antioxidative activity of phenolic acids on triacylglycerols and fatty acid methyl esters from olive oil

The autoxidation of kinetically pure triacylglycerols and methyl esters of olive oil (TGOO and MEOO) in the presence of four different concentrations of p-coumaric, ferulic and caffeic acids at 100 degrees C was studied. It was established that effectiveness and strength of the phenolic acids were greater in MEOO than in TGOO. In both lipid substates the molecules of phenolic acids participate in one side-reaction (with hydroperoxides). The rate constants of this reaction in TGOO and in MEOO are practically the same. The phenolic acids take part in chain initiation. The rate of this reaction for ferulic and caffeic acids has equal values in TGOO and in MEOO, whereas for p-coumaric acid it is twice as high in TGOO than in MEOO. The radicals of the phenolic acids participate in one reaction of chain propagation (with the lipid substrate) both in triacylglycerols and in methyl esters of olive oil. Comparison with the data published recently for sunflower oil triacylglycerols and methyl esters demonstrates the strong influence of the unsaturation type and degree of the lipid system on the kinetics and mechanism of the antioxidative action of the phenolic acids. Copyright (C) 1996 Elsevier Science Ltd