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 geometrictrans,cis‐ andtrans, 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 peroxidehydroperoxides, 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.

Metabolism of Linoleic Acid by Barley Lipoxygenase and Hydroperoxide Isomerase

“…DISCUSSION Hydroperoxide ratios determined in this study were quite different from those based on gravimetric (6) or mass spectral analysis of each methyl hydroxystearate derivative (25). Other published methods used to obtain these ratios have been questioned because sodium borohydride reduction followed by hydrogenation causes chemical isomerization (21), nonsilylated hydroxystearates do not respond as quantitatively as trimethylsilyl ethers when analyzed by , and mass spectral quantitation of hydroxystearates requires computer summation of the diagnostic ions within the GC peak (4).…”

Chemical changes in lipids produced by thermal processing

“…In addition, they may undergo autoxidation via the free radical chain reaction mechanism outlined above, giving rise to shorter-chain aldehydes, dialdehydes, hydrocarbons, etc., or epoxidation and cleavage as shown in Figure 4 for W d e c a dienal (15), or condensation to form trioxanes and dioxolanes (16).…”

Effect of the Amount of Liquid Phase in Packed Column GC on Air Oxidation Product of Methyl Oleate

“…This fatty acid is easily oxidized by air and produced various kinds of oxygenated compounds. It is well-known that the first product from oleic acid methyl ester (OM) is methyl hydroperoxyoleate (OMH) 1) , which consists of four kinds of positional isomers. If a metal salt coexists, the second products 2) were produced more remarkably.…”

“…In particular, GC/MS, which uses a mass spectrometer (MS) as a detector, possesses higher reliability because it uses molecular weight for determining the separated components in addition to the retention time of chromatography. Frankel et al determined the positional isomer by reducing OMH 1) and methyl hydroperoxylinoleate 3) to hydroxides using the GC/MS with a packed column (glass 14 ft 4 mm id, 10% OV-101 on Chromosorb G). Moreover, a study determining the epoxy hydroxide using the GC/MS with a capillary column, which has been developed after 1980, with an open tubular glass column (length 25 m, film thickness 0.33 mm, methyl silicone) has been reported 4) .…”

“…Two-dimension at proton NMR spectra showed characteristic signals indicative of allylic hydroperoxide at 5.78 ppm for -CH(OOH)-CH=CH-, at 5.36 ppm for -CH(OOH)-CH=CH-, at 4.25 ppm for -CH(OOH)-CH=CH-, at 2.08ppm for -CH(OOH)-CH=CH-CH 2 -, and at l.62 ppm for -CH 2 -CH(OOH)-CH=CH-. The authentic standard of methyl hydroperoxyoleate is a mixture of four positional isomers, i.e., methyl 8-hydroperoxy-9-, 9-hydroperoxy-10-,10-hydroperoxy-8-, and 11-hydroperoxy-9-octadecenoates 3) . Methyl a-hydroxyepoxystearate (methyl a-hydroxyepoxyoctadecanoate) was prepared by epoxidation 8) of methyl ahydroxyoleate that was produced by reduction of the hydroperoxides.…”