Identification and quantitation of trans-9,trans-12-octadecadienoic acid methyl ester and related compounds in hydrogenated soybean oil and margarines by capillary gas chromatography/matrix isolation/fourier transform infrared spectroscopy
1990
Mossoba, M.M. | McDonald, R.E. | Chen, J.Y.T. | Armstrong, D.J. | Page, S.W.
The processing of vegetable oils by hydrogenation leads to the isomerization of cis unsaturated fatty acids. The resulting trans-9,trans-12-18:2 isomer is of concern because it was reported to disrupt the metabolism of essential fatty acids and to influence the synthesis of prostaglandins and other cell regulators. Geometric (cis or trans) and positional isomers in catalytically hydrogenated soybean oil and margarines have been separated as fatty acid methyl esters (FAMEs) by capillary gas chromatography (GC) using a polar cyanopropylpolysiloxane liquid-phase column. This paper demonstrates that the unique matrix isolation/Fourier transform infrared (MI/FT-IR) spectral bands due to the =C-H stretch and the out-of-plane deformation vibrations are highly characteristic of the number and configuration of the double bonds in FAME isomers. By using GC/MI/FT-IR, C18 FAME isomers from hydrogenated soybean oil and margarines were identified, and the presence of four trans, trans-diene isomers in one of the hydrogenated soybean oil test samples is reported. FAMEs containing trans double bonds were quantified. The amounts of the trans-9,trans-12-18:2 isomer found in the margarines investigated were low (0.3%).
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