Autoxidation of Unsaturated Fatty Acid Methyl Esters. I.

Methyl oleate and methyl elaidate were autoxidized in the conditions free from natural antioxidants and metals. The autoxidation of methyl oleate gave the rate 10.4 times as fast as that found for methyl elaidate in comparison of the induction period, and 2.2 times in comparison of the rate of the oxidative weight increase and the hydroperoxide formation rate after the induction period. Results from analyses of the various autoxidation products from oleate and elaidate showed that the autoxidation products from oleate were formed in a shorter interval of autoxidation in comparison with those from elaidate, but the amount of the autoxidation products from oleate was similar to that from elaidate if the autoxidation products were compared at the same autoxidation level (oxidative weight gains). These results showed that the different rates of the autoxidation between oleate and elaidate resulted from the different affinity of oxygen molecule with the olefinic double bond of substrates (equations 7 and 8).