Contribution of the formation of oxidized lipid amino acid reaction products to the protective role of amino acids in oils and fats

The antioxidative activity of n-octylamine, N-methylheptylamine, and N,N-dimethylhexylamine in a soybean oil was evaluated in order to investigate if this antioxidative activity might be related to their different abilities to produce oxidized lipid/amine reaction products (OLARP). The three amines were added at live levels of concentration 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. When added at 100 or 200 ppm, n-octylamine and N-methylheptylamine, but not N,N-dimethylhexylamine, decreased TBARS production in the soybean oil. The three amines, when added at higher concentrations, exhibited a high antioxidative activity, and no big differences among them were observed. Because only primary and secondary amines are able to produce antioxidative OLARP, the differences observed on antioxidative activity at 100 and 200 ppm are in agreement with a contribution of the protective effect of OLARP formation. This hypothesis was confirmed by detection of some OLARP in a soybean oil incubated in the presence of 200 ppm of n-octylamine for 240 h. In addition to OLARP formation, other processes should also be implicated so that the antioxidative activities observed for the three amines at higher concentrations could be explained.