EFFECT OF LIPID UNSATURATION ON THE ANTIOXIDATIVE ACTIVITY OF SOME PHENOLIC-ACIDS

Antioxidative properties of phydroxybenzoic, vanillic, syringic, 3,4-hydroxybenzoic, p-coumaric, ferulic, sinapic and caffeic acids were studied in the concentration range 0.02-0.20 wt% during autoxidation at 100 degrees C of lard and sunflower oil methyl esters (MEL and MESO, respectively). In both lipid systems, the derivatives of benzoic acid had weaker inhibiting properties than did the corresponding analogues of cinnamic acid. The effectiveness and strength of the antioxidative action were considerably lower in the lipid system MESO, which was rich in linoleic acid and was more easily oxidized. The p-hydroxybenzoic, vanillic, syringic and p-coumaric acids in this system exercised no inhibiting effect. We established that the molecules of the investigated phenolic acids initiated the chain radical process of autoxidation, and the formed antioxidant radicals propagated the chains as a result of the reaction with the lipid substrate. These reactions proceeded at a higher rate in MESO than in MEL.