Analyses of fatty acid isomers in two commercially hydrogenated soybean oils

Abstract

A conventional shortening and a hydrogenated winterized oil have been investigated to determine their composition of natural and isomeric fatty acids. Two solvent systems were applied in countercurrent distributions: the acetonitrile pentane‐hexane system for separation of monoenoates from dienoates and the methanolic silver nitrate pentane‐hexane system for separation of geometric isomers. Whilecis andtrans monoenoates were well resolved, the separation ofcis,cis fromcis,trans dienoates was complicated by the presence of positional isomers. The fractions isolated were oxidatively cleaved, and the esters of the resultant acids were quantitatively analyzed by gas‐liquid chromatography.Although the amounts of saturated components of the two fat products were similar, the percentage oftrans isomers of the shortening was more than twice that of the winterized oil. The amount of oleic acid (cis‐9‐octadecenoic) was 19.6% for the shortening and 25.4% for the winterized oil. The shortening contained 13.3% linoleic acid (cis,cis‐9,12‐octadecadienoic), whereas the winterized oil contained 30% linoleic acid.Although our primary interest was in the estimation ofcis‐9‐octadecenoic andcis,cis‐9,12‐octadecadienoic acids, the completeness of cleavage data makes it possible to estimate all geometric and positional monoenoate and dienoate isomers in the two fat products.