Gas Chromatography Mass Spectrometric Analysis of Monohydroperoxide Isomers and Their Secondary Oxidation Products of Methyl Linoleate and Methyl Linolenate

Abstract

Emulsions of methyl linoleate monohydroperoxides (18:2-monoHP) and methyl linolenate monohydroperoxides (18:3-monoHP)were incubated with ferrous sulfate and ascorbic acid. Gas chromatography mass spectrometric analysis of the trimethylsilyl and ter/-butyldimethylsilyl derivatives of the reaction products showedthat isomerization and secondary oxidation happen competitively during decomposition of 18:2-monoHP, while the secondary oxidation reaction proceeds preferentially and little isomerization is observed in 18:3-monoHP. It is suggested that 18:3-monoHP is more susceptible to secondary oxidation than 18:2-monoHP because of 18:3 specific secondary oxidation resulting in hydroperoxy-cyclic peroxides and dihydroperoxides. Moreover, an experiment using ¹⁸O₂ has demonstrated that molecular oxygen is scrambled by isomerization and secondary oxidation. It was confirmed that molecular oxygen is attached preferentially to the C-13 position in the 9-monoHPisomer and C-9 position in the 13-monoHP isomer during degradation of 18:2-monoHP.