Evaluation of the effects of allyl isothiocyanate and diallyl disulfide on the trans isomerization of unsaturated fatty acids during heat treatment

According to previous studies, the intake of trans fatty acids (TFAs) increases the risk of cardiovascular diseases. Although edible oils with low TFA contents have been produced by fractionation and transesterification, few studies have evaluated the effects of food ingredients on the trans isomerization of unsaturated fatty acids during cooking. Thus, this study evaluated the effects of allyl isothiocyanate (AITC) and diallyl disulfide (DADS), which are widely found in vegetables, on the thermal isomerization of unsaturated fatty acid esters. When a solution of methyl oleate in dodecane was heated in an air-filled glass tube with AITC and/or DADS, trans isomerization was significantly promoted. For example, when the methyl oleate solution was heated at 180 °C for 1 h in the presence of 1.0 equivalent of AITC or DADS, its trans isomer ratio reached 67.9 ± 1.6 or 6.4 ± 0.2%, respectively (Figure 1). Interestingly, the simultaneous addition of AITC and DADS did not have any additive or synergistic effects but rather decreased the trans isomerization of methyl oleate compared with that achieved with the addition of AITC alone. The addition of α-tocopherol (1 wt% with respect to methyl oleate) also suppressed trans isomerization. However, α-tocopherol had a lower suppression effect on DADS than on AITC (Figure 2). These results indicate that isothiocyanates and polysulfides can promote the formation of TFAs in food processed by heating, but their effect could be suppressed by other ingredients or antioxidants in the food.