Effects of the addition of amino acids and peptides on lipid oxidation in a powdery model system

The effects of the addition of amino acids and peptides on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) were investigated. The encapsulated lipid was prepared in two steps, that is, by mixing of EPE with MD solutions (+/-amino acids and peptides) to produce emulsions and freeze-drying of the resultant emulsions. The addition of amino acids and peptides improved the oxidation stability of EPE encapsulated with MD, and the inhibition of lipid oxidation by the amino acids and peptides was more effective at 70% relative humidity (RH). Met, Arg, and Trp were effective amino acids for antioxidation at RH = 10 and 40%, whereas at RH = 70%, His was the most effective amino acid, preventing the oxidation of EPE almost perfectly. Carnosine also exhibited a strong antioxidant effect at RH = 70%, but the effect of anserine was inferior. The addition of Met + Trp or Met + Arg inhibited the oxidation of EPE encapsulated with MD at RH = 40%. Cys accelerated the oxidation of EPE, indicating that the thiyl radical may act as a pro-oxidant. No close relationship was observed between the radical scavenging abilities of amino acids and peptides measured in the aqueous diphenylpicrylhydrazyl solution and their antioxidative effects in the powdery system. It is possible that the radical-scavenging ability of amino acids and peptides detected by ESR in the powder system is responsible for the antioxidative activity of these compounds.