ISOMERIC DISTRIBUTION AND RAPID-DETERMINATION OF TRANS-OCTADECENOIC ACIDS IN GERMAN BRANDS OF PARTIALLY HYDROGENATED EDIBLE FATS

The determination of trans fatty acids (TFA), in particular trans-octa decenoic acids, in edible fats is of current interest, since just in t he last years a variety of negative physiological effects has been rel ated to TFA. A main source of C18:1 trans fatty acids are partially hy drogenated fats. Besides the total content of trans-octadecenoic acids , their isomeric distribution seems to be even more important, as fats of different origin, e.g, partially hydrogenated fats and ruminant fa ts, possibly show different physiological properties. In this study, 4 6 margarines and 16 shortenings and cooking fats, purchased in August of 1994, were analyzed for trans-octadecenoic acid isomers by a two-st ep method (Ag-TLC/HRGC). The mean relative isomeric distributions (g/1 00 g TFA) of both groups determined with a 100 m-column were comparabl e, with Delta 9 and Delta 10 being the main isomers. By repeated analy sis of 15 brands between August of 1994 and January of 1996, the mean total C18:1 TFA content was found to have decreased in these margarine s (n=8) from 9.58% to 4.62% but not in shortenings/cooking fats (n=7; 11.62% to 11.92%). The relative isomeric distribution was not affected in both groups. To avoid the problem of overlaps between cis- and tra ns-C18:1 isomers with GC analysis, formulae for the rapid determinatio n of total C18:1 TFA contents in margarines and shortenings/cooking fa ts from direct GC data were statistically derived. Thus, applying thes e formulae and considering the mean relative distributions, absolute c ontents of ail individual isomers of trans-octadecenoic acids can rapi dly be deter mined from direct GC.