The potential of lysine to extend the shelf life of soybean oil evidenced by 1H Nuclear Magnetic Resonance

The effect of 1% and 2% proportions of L-lysine on the oxidation process of soybean oil, performed at 70 degrees C under stirring conditions, has been studied by H-1 Nuclear Magnetic Resonance. This technique allows one to monitor the generation and further evolution of a wide variety of oxidation products (hydroperoxides, epoxides, aldehydes, keto-dienes and hydroxy-derivatives), providing a comprehensive view of the oxidation process. The addition of lysine considerably delays the degradation of the oil acyl groups and the generation of both primary and secondary oxidation compounds, while preserving the oil content of gamma-tocopherol for longer, especially at the highest enrichment level. A diminution in the maximum concentration reached by some types of secondary oxidation products is also observed in the lysine-enriched samples. This is particularly noticeable for aldehydes, whose concentration is markedly reduced, above all that of the toxic oxygenated alpha,beta-unsaturated ones, probably due to their reaction with lysine. Therefore, the ability of lysine to extend the shelf life of soybean oil is proved in this work, as well as its feasibility as a potential antioxidant for use in lipidic foods. These findings could also contribute to a better understanding of the antioxidant effect of proteins.