Antioxidative activity of lysine/13-hydroperoxy-9(Z),11(E)-octadecadienoic acid reaction products

The antioxidative activity of the reaction products formed in the reaction between 13-hydroperoxy-9(Z),11(E)-octadecadienoic acid (13-LOOH) and L-lysine was evaluated to determine if the reaction of lipid hydroperoxides with amino acids produces compounds that are able to protect lipids against oxidation. A reaction mixture of 13-LOOH and lysine was incubated for 8 days at 37 degrees C and, then, fractionated chromatographically by using silica cartridges. The four fractions obtained in this way were added at two levels of concentration (100 and 200 ppm) to soybean oil, which was oxidized under air in the dark at 60 degrees C. Oil peroxidation was evaluated by using the thiobarbituric acid-reactive substances (TBARS) assay. The less polar fraction obtained, which was eluted with 2-propanol, did not decrease TBARS production in the soybean oil. However, the other three fractions were able to significantly (P < 0.05) reduce TBARS production, suggesting that the reaction of lipid hydroperoxides with amino acids produces compounds with antioxidative properties. These reactions may contribute to a decrease of the lipid peroxidation process in foods containing proteins.