Oxidative Stability of Geometric and Positional Isomers of Unsaturated Fatty Acids in Aqueous Solution

Abstract

The geometric and positional isomers of monoenoic, dienoic and trienoic fatty acids were oxidized in aqueous solution using Fe2+-ascorbic acid as the catalyst. The oxidative stability of each acid was assessed based on decrease in unoxidized substrate content. The trans and cis isomers of dienoic and trienoic acids were found to differ in stability while this parameter for trans isomers of monoenoic acids was essentially the same as that of the cis isomers. The oxidative stability of monoenoic acid increased with the proximity of olefinic bonds to methyl ends and shortness of chain length. The effect of chain length on oxidative stability was the same for isomers of methylene-interrupted trienoic acids. In aqueous solution, oleic acid was more oxidatively stable than linoleic acid, but oxidized more rapidly than α-linolenic acid. This order for the oxidative stability of unsaturated C18 acids was different from that in air. The relative oxidative stability of nonmethylene-interrupted dienoic and trienoic acids in aqueous solution also differed from that in air.