Degradation of fatty acid methyl esters by gamma-ray irradiation

Abstract

　　There is a few information on the effect of γ-ray irradiation on the structure of fatty acid methyl ester (FAME). In this study, we examined the radiolysis of FAMEs, such as methyl stearate (C18:0), methyl oleate (MO, C18:1), methyl linoleate (MLa, C18:2), methyl linolenate (MLn, C18:3), and methyl α-eleostearate (MESA, C18:3, purity 70.9 wt/wt%). In hexane, the degradation percentages in the air condition, were higher than those in nitrogen atmosphere because of the formation of free radicals during the γ-ray irradiation. The degradation percentage of FAMEs were affected positively by the irradiation dose of γ-ray and the initial FAME concentration. The degradation percentages were higher in methanol than those in hexane. The degradation percentages of FAMEs increased with an increase in the number of double bonds in their molecular structures (r ² = 0.98–1.0) (P < 0.05). However, since MESA has three conjugated double bonds, its degradation percentage was more rapid. The radiolysis products of FAMEs using γ-ray irradiation were detected using capillary gas chromatography – mass spectrometry. The results of the radiolysis product of FAMEs indicated that the degradation proceeded by two processes: direct ionization by energetic photons (in which hydrocarbons and low molecular weight FAMEs are produced) and indirect irradiation by hydroxyl radicals generated from methanol or trace water in hexane (in which aldehydes and alkenes were produced).