Vegetables containing sulfur compounds promote trans-isomerization of unsaturated fatty acids in triacylglycerols during the cooking process.

Growing evidence indicates that the intake of trans-fatty acids (TFAs) has been associated with a higher risk of cardiovascular disease; therefore, various industrial measures have been taken to reduce the amount of TFAs consumed. However, research on TFAs formed during cooking is limited. Isothiocyanates and polysulfides, which are widely distributed in various vegetables, have recently been shown to promote the cis-trans isomerization of double bonds. However, the effects of these sulfur compounds on unsaturated fatty acids (UFAs) comprising edible oils (triacylglycerols) are unknown. To further reduce the intake of TFAs, a better understanding of the effect of the presence of these sulfur compounds on the formation of TFAs under cooking conditions is important. This study investigated the isomerization characteristics of UFAs in the presence of isothiocyanates and polysulfides in model systems using high-purity compounds as well under simulated cooking conditions using food samples. The outcomes of the model system indicated that these sulfur compounds significantly enhance the thermal isomerization, especially at temperatures ≥140 °C. Furthermore, the addition of antioxidants substantially inhibited the isomerization enhancement effect of isothiocyanates, whereas that of polysulfides was marginally moderated. A similar trend was observed under simulated cooking conditions. The results suggest that cooking with sulfur-compound-rich vegetables, especially garlic and onion, which are rich in polysulfides, can potentially result in increased trans fatty acid intake.