Evaluating the Content and Distribution of Trans Fatty Acid Isomers in Foods Consumed in Japan.

Trans fatty acids (TFA) are considered risk factors for cardiovascular disease. However, detailed information on total content of TFA and TFA isomers and distribution of trans-octadecenoic acid positional isomers in foods consumed in Japan is not available till date. In this study, 250 foods, 169 processed foods and 81 foods derived from ruminant meat or milk, were analyzed. According to the results, most foods contained less than 1.0 g TFA / 100 g food. However, almost all foods containing butter had more than 1.0 g TFA / 100 g food. TFA isomers in foods were classified into two categories, monoene-rich type and polyenerich type. We hypothesized that these differences were attributed to diverse TFA formation mechanisms. Furthermore, we observed that trans-10-18:1 was also the dominant trans-18:1 positional isomer in foods consumed in Japan. These results are valuable for future analysis of the role of TFA in epidemiological studies in Japan.

Study of Trans Fatty Acid Formation in Oil by Heating Using Model Compounds.

The intake of trans fatty acids (TFAs) in foods changes the ratio of low density lipoprotein (LDL) to high density lipoprotein (HDL) cholesterol in blood, which causes cardiovascular disease. TFAs are formed by trans isomerization of unsaturated fatty acids (UFAs). The most recognized formation mechanisms of TFAs are hydrogenation of liquid oil to form partially hydrogenated oil (PHO,) and biohydrogenation of UFAs to form TFA in ruminants. Heating oil also forms TFAs; however, the mechanism of formation, and the TFA isomers formed have not been well investigated. In this study, the trans isomerization mechanism of unsaturated fatty acid formation by heating was examined using the model compounds oleic acid, trioleate, linoleic acid, and trilinoleate for liquid plant oil. The formation of TFAs was found to be suppressed by the addition of an antioxidant and argon gas. Furthermore, the quantity of formed TFAs correlated with the quantity of formed polymer in trioleate heated with air and oxygen. These results suggest that radical reactions form TFAs from UFAs by heating. Furthermore, trans isomerization by heating oleic acid and linoleic acid did not change the original double bond positions. Therefore, the distribution of TFA isomers formed was very simple. In contrast, the mixtures of TFA isomers formed from PHO and ruminant UFAs are complicated because migration of double bonds occurs during hydrogenation and biohydrogenation. These findings suggest that trans isomerization by heating is executed by a completely different mechanism than in hydrogenation and biohydrogenation.