Characterization, quantitation and evolution of monoepoxy compounds formed in model systems of fatty acid methyl esters and monoacid triglycerides heated at high temperature

Monoepoxy compounds formed after heating methyl oleate and linoleate, triolein and trilinolein at 180 degrees C for 5, 10 and 15 hours, were characterized and quantitated after derivatization to fatty acid methyl esters by using two base-catalyzed procedures. Structures were identified by GC-MS before and after hydrogenation. A complete recovery of the epoxy compounds was obtained by comparing results from methyl oleate and linoleate before and after transesterification, and good repeatability was also attained. Similar amounts of epoxides were found for methyl esters and triglycerides of the same degree of unsaturation, although formation was considerably greater for the less unsaturated substrates, methyl oleate and triolein, possibly due to the absence of remaining double bonds in the molecule which would involve a lower tendency to participate in further reactions. On other hand, independently of the degree of unsaturation of the model systems and of the period of heating, significantly higher amounts of trans isomers were formed. Finally, from comparison between the amounts of epoxides and the level of polar fatty acids in samples, it was deduced that monoepoxy compounds were one of the major groups formed under the conditions used.