EFFECTS OF ANTIOXIDANTS ON THE STABILITY OF TRIACYLGLYCEROLS AND METHYL-ESTERS OF FATTY-ACIDS OF SUNFLOWER OIL

The autoxidation of kinetically pure triacylglycerols and methyl ester s of sunflower oil (TGSO and MESO) in the presence of four different c oncentrations of 3,4-dihydroxybenzoic, ferulic, sinapic and caffeic ac ids, and in the absence of metal ions, at 100 degrees C was studied. I t was established that the effectiveness and strength of the phenolic acids was greater in TGSO than in MESO. The interpretation of the resu lts by kinetic and computational methods allowed the mechanism of acti on of the antioxidants to be elucidated. In both lipid substrates the molecules of the phenolic acids participate in one side reaction. The rate constants of this reaction in TGSO and MESO are practically the s ame, which shows that the binding of the fatty acids to the triacylgly cerol structure of the sunflower oil does not change the mechanism of phenolic acid consumption in side reactions. The phenolic acids partic ipate in reactions of chain initiation, which have a three to six time s higher rate in MESO than in TGSO. The radicals of 3,4-dihydroxybenzo ic, sinapic and caffeic acids in MESO, and of 3,4-dihydroxybenzoic and caffeic acids in TGSO, take part in one reaction of chain propagation (with the lipid substrate). The radicals of ferulic acid in MESO, and of ferulic and sinapic acids in TGSO, participate in more than one re action of chain propagation. The effectiveness and strength of the phe nolic acids are higher in TGSO than in MESO because, during the oxidat ion of TGSO, the contribution of the inhibitor radicals and molecules to chain initiation and propagation is smaller than in the case of MES O oxidation.