Levels of Trans Geometrical Isomers of Essential Fatty Acids in Some Unhydrogenated U. S. Vegetable Oils¹

Concentrations of trans isomers of 18:2w6 and 18:3w3 were measured in soybean and canola oils purchased in the U. S. Fatty acid methyl esters were prepared by BF 3 catalyzed transesterification and separated using gas chromatography with Omegawax and CPSil88 capillary columns. Fatty acids were identified by comparing retention times with standards and with isomers of 18:2w6 and 18:3w3 in elaidinized linseed oil. Isomers identified included 18:2ct, 18:2tc, 18:3tct+ctt, 18:3cct, 18:3ctc, and 18:3tcc. The degree of isomerizations of 18:2w6 and 18:3w3 ranged from 0.3% to 3.3% and 6.6% to 37.1%, respectively. The trans contents were between 0.56% and 4.2% of the total fatty acids. Consumers will obtain isomerized essential fatty acids from vegetable oils currently marketed in the U. S.