In a one-step extraction/methylation (OSM) method for determining individual fatty acids (FA) in processed food products, freeze-dried samples, containing 10-50 mg fat, were transmethylated without prior fat extraction with a mixture of methanol-HCl/toluene. After washing the organic phase the formed FA methyl esters were ready for separation by gas-liquid chromatography (GLC). The relative standard deviation for total FA content was <3.5%, regardless of the food type analyzed. Furthermore, the FA composition of selected fatty foods as obtained by the OSM procedure was almost identical with the FA composition of the pure fats extracted by the Soxhlet procedure and with chloroform-methanol, respectively. The OSM method is inexpensive and simple to perform and is, therefore, well suited for nutrient labeling studies, especially in situations where many samples have to be analyzed for their total FA content.

Trans fatty acids (TFA) formed during biohydrogenation by ruminant animals were quantified in cows' milk fat by means of Fourier transform i.r. (FTIR) spectroscopy. When samples were analysed as the derived methyl esters, a spectral subtraction technique resulted in TFA values that were not biased by the unspecific absorption of intact triacylglycerols or influenced by the shape of the trans band. Austrian milk fat samples contained 20-50 g TFA/kg. Results obtained by analysis of TFA as triacylglycerols compared favourably with those obtained by using methyl esters. The findings of the FTIR method were further substantiated by applying argentation chromatography in combination with capillary gas chromatography to the same set of samples. Besides trans monoenoic acids, non-methylene interrupted cis, trans octadecadienoic acids contributed significantly to the total trans content. Two novel TFA, trans-ll, cis-15 octadecadienoic and cis-d, trans-13 octadecadienoic acids, were identified in milk fat by means of their retention behaviour on argentation chromatography and gas chromatography as well as by an oxidative degradation procedure.

Several modifications of an established thin‐layer chromatography‐gas‐liquid chromatography (TLC‐GLC) procedure for quantitatingtrans unsaturated fatty acids in edible fats are presented. These refinements considerably simplify the procedure without affecting accuracy. The modifications include: i) the use of pre‐coated silica sheets, dynamically impregnated with Ag+, which allow separated bands to be cut off with a pair of scissors; and ii) the use of stearic acid in the deliberately combined saturated andtrans monounsaturated fatty acid methyl ester bands as an (endogenous) internal standard.Trans values thereby obtained agree favorably with the results from the conventional technique.

Margarines and shortenings available in Austria were repeatedly sampled in 1991/1992 and the content of trans fatty acids (TFA) determined by using capillary GLC. Wide variations of the TFA contents with respect to intra- and inter-brand differences were observed. Diet margarines contained up to 1% TFA, while TFA concentrations in tub or stick margarines were much higher (15.7 +/- 5.8% and 21.3 +/- 5.3%, respectively). A sub-set of samples was also purchased in 1995 and a general reduction of the TFA content was noticed. Taking into account different market shares of certain margarine types, a weighted average of 15.7% TFA and 6.5% TFA was calculated for the 1991/1992 and the 1995 samples. Based on availability data the amount of TFA supplied with margarines was estimated to be 3.7 g per person per day, while a more accurate method of measuring dietary intakes, i.e. diet history and food frequency data, approximates the amount of TFA supplied with margarines to be 1.5 g per person per day for the 1991/1992 samples and 0.6 g for the 1995 samples.

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