Autoxidative rates of nonmethylene-interrupted polyenoic fatty acids

Autoxidative rates of free fatty acids and methyl esters increased in the following order: oleic (c9–18:1), c5, c9–18:2, linoleic (c9,c12–18:2), c5,c9,c12–18:3, t5,c9,c12–18:3, and linolenic (c9,c12,c15–18:3). The increase of the rates due to the Δ5-olefinic bond was much lower than that due to an olefinic bond extension in a methylene-interrupted sequence. Agreement of the oxidative rates obtained from conjugated diene content with those obtained from POV showed that oxygen attack did not occur at the isolated olefinic bond, but at the methylene-interrupted diene in the oxidation of 5,9,12–18:3. The Δ5-olefinic bond may promote the oxidation of the methylene-interrupted diene intramolecularly.