Analysis of autoxidized fats by gas chromatography mass spectrometry: III. Methyl linolenate

Abstract

The gas chromatography-mass spectrometry (GC-MS) method developed in the preceding papers was extended to the analysis of autoxidation products of methyl linolenate. Four isomeric hydroxy allylic trienes with a conjugated diene system were identified after reduction of the linolenate hydroperoxides. All eight geometric trans,cis- and trans, trans-conjugated diene isomers of these hydroxy allylic compounds were identified and partially separated by GC of the trimethylsilyl (TMS) ether derivatives. The proportion found of 9- and 16-hydroperoxides was significantly higher (75-81%) than the 12- and 13-hydroperoxides (18-25%). The tendency of the 12- and 13-hydroperoxides to form cyclic peroxides, cyclic peroxide-hydroperoxides, and prostaglandin-like endoperoxides was supported by indirect evidence for the presence of 9,10,12- and 13,15,16-trihydroxyoctadecanoate in hydrogenated derivatives of the highly oxygenated products. The quantitative GC-MS method was used to determine the relative contribution of linolenate, linoleate, and oleate in mixtures to the formation of hydroperoxides.