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Trans fatty acids (TFA) are supposed to be related to a variety of physiological effects. Numerous studies in this field are gathered and compared, which mainly deal with the influences on lipoprotein levels in plasma and their effects with regard to coronary heart diseases. Furthermore, the analytical accessibility of trans fatty acids by different methods is presented. Thus, the most reliable method for an exact quantitation of trans fatty acids in edible fats is the combination of Ag-TLC with GC. The contents of TFA, in particular trans-octadecenoic acids, in bovine and human milk fat, in partially hydrogenated vegetable fats and oils as well as in processed food from different countries, determined in numerous studies, are summarized. Especially results on the isomeric distribution of positional isomers of trans-octadecenoic acid may be of future interest, since negative metabolic activities might only originate from certain isomers. Finally, intake rates of TFA in several countries are presented. It can be concluded that there still is need for further nutritional studies and that the discussion about TFA should not neglect the comparison with the saturated fatty acids C12, C14 and C16.

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A survey of the total content of trans-18:1 acids and their detailed profile in French food lipids was conducted in 1995-1996, and 1999. For this purpose, 37 food items were chosen from their label indicating the presence of partially hydrogenated vegetable oils (PHVO) in their ingredients. The content as well as the detailed profile of these isomers was established by a combination of argentation thin-layer chromatography and gas liquid chromatography (GLC) on long polar capillary columns. With regard to the mean trans-18:1 acid contents of extracted PHVO, a significant decrease was observed between the two periods, i.e., from 26.9 to 11.8% of total fatty acids. However, only minor differences were noted in the mean relative distribution profiles of individual trans-18:1 isomers with ethylenic bonds between positions delta4 and delta16 for the two periods. The predominant isomer was delta9-18:1 (elaidic) acid, in the wide range 15.2-46.1% (mean, 27.9+/-7.2%) of total trans-18:1 acids, with the delta10 isomer ranked second, with a mean of 21.3% (range, 11.6 to 27.4%). The content of the unresolved delta6 to delta8 isomer group was higher than the delta11 isomer (vaccenic acid), representing on average 17.5 and 13.3%, respectively. Other isomers delta4, delta5, delta12, delta13/delta14, delta15, and delta16, were less than 10% each: 1.0, 1.6, 7.4, 7.1, 1.8, and 1.0%, respectively. However, considering individual food items, it was noted that none of the extracted PHVO were identical to one another, indicating a considerable diversity of such fats available to the food industry. A comparison of data for French foods with similar data recently established for Germany indicates that no gross differences occur in PHVO used by food industries in both countries. Estimates for the absolute mean consumption of individual isomers from ruminant fats and PHVO are made for the French population and compared to similarly reconstructed hypothetical profiles for Germany and North America. Differences occur in the total intake of trans-18:1 acids, but most important, in individual trans-18:1 isomer intake, with a particular increase of the delta6-delta8 to delta10 isomers with increasing consumption of PHVO. It is inferred from the present and earlier data that direct GLC of fatty acids is a faulty procedure that results (i) in variable underestimates of total trans-18:1 acids, (ii) in a loss of information as regards the assessment of individual isomeric trans-18:1 acids, and (iii) in the impossibility of comparing data obtained from human tissues if the relative contribution of dietary PHVO and ruminant fats is not known.

A representative number of different milk fats based on a wide range of feeding and lactation conditions as well as 123 German margarines, shortenings, cooking and dietetic fats were analyzed for a variety of trans-C18:2 isomers (exhibiting at least one trans double bond) by. means of gas chromatography on a 100 m Sil 88 capillary column. In milk fats contents of trans A9,trans A12, cis A9,trans A13 (+ trans A8,cis A12), trans A8,cis A13, cis A9,trans A12, trans A9,cis A12 and trans Al1,cis A15 amounted to 0.09%, 0.1146, O.ll%, 0.10%, 0.m and 0.334/0 on average and the content of total trans-C18:2 isomers (without cis A9,trans All) was 0.99% in the mean. The content of conjugated linoleic acid cis A9,trans A l l amounted to 0.81% on average in 238 milk fats. In margarine among others the isomers trans A9,trans A12, cis A9,trans A13 (+trans A8,cis A12), cis A9, trans A12 and trans A9,cis A12 were determined and quantified to 0.03%, 0.0446, 0.29% and 0.23% on average. The mean total content of trans-C18:2 isomers in margarines was 0.61%. Moreover, for all trans-C18:2 isomers the frequency distributions as well as the correlation coefficients towards the trans-Cl8:l isomers trans A6 to trans A16 were derived.Tr8nsgeometrische und Positionsisomere der Linolslure einschlieslich der konjugierten Linolsaure (CLA) in deutschen Milch-und Pflanzenfetten. Von einer reprasentativen Anzahl verschiedener Milchfette, welchen unterschiedliche Fiitterungs-und Laktationsbedingungen zugrunde lagen, sowie von 123 deutschen Margarinesorten, Back-, Brat-und Diatfetten wurden verschiedene trans-C18:2-Isomere (mit mindestens einer trans-Doppelbindung) mit Hilfe einer 100 m langen Sil 88-Kapillarsaule gaschromatographisch bestimmt. Im Milchfett konnten hierbei Gehalte an trans A9, trans A12,cis A9, trans A13 (+ trans A8,cis A12), trans A8,cis A13, cis A9,rrans A12, trans A9,cis A12 und trans All@ A15 von im Mittel 0,09%, 0,11%, 0,11%, 0,10%, 0,m und 0,33% sowie aller trans-C18:2-Isomere (ohne cis A9,frans All) von 0,99% bestimmt werden. Die konjugierte Linolsaure cis A9,trans A1 1 trat in 238 analysierten Milchfetten im Mittel zu 0.81% auf. In Margarine wurden u.a. von den Isomeren trans A9,trans A12, cis A9,trans A13 (+ trans A8,cis AlZ), cis A9,trans A12 und trans A9,cis A12 Anteile von 0,034/0, 0,04%, 0,29% und 0,23% sowie ein mittlerer Gehalt aller trans-C18:2-Isomere von 0,61% nachgewiesen. Weiterhin wurden von allen trans-C18:2-Isomeren die Haufigkeitsverteilungen bestimmt und Korrelationen zu den trans-C18:l-Positionsisomeren trans A6 bis trans A16 abgeleitet.