Formation And Control Of Trans Fatty Acids In Edible Oils During Heat Treatment

Since previous studies suggested that trans fatty acids (TFAs) had an adverse effect on human health, considerable attention on determination, formation and reduction of TFAs have been taken in recent years. Partially hydrogenated oils are considered to be the major source of TFAs in the diet. However, the formation of TFAs in edible oils during heating process can’t be ignored. At present, the majority of the study of reduction of TFAs is mainly focusing on oil hydrogenation, there is a lack of systematic research on TFAs formation inedible oils during heat treatment. It is significantly important to know the path of TFAs formation so as to find a way to reduce the TFAs in edible oils during heating process. Besides, studying the effect of anti-oxidants on reducing the formation of TFAs in edible oils and investigating the relevant inhibition mechanisms are the hot topics and difficulties. In this study, formation and control of TFAs in edible oils during heat treatment were investigated.At first, a simple and sensitive gas chromatography (GC) method based on a GC method developed by American Oil Chemists’ Society (AOCS) was established to determine TFAs by optimizing the derivation and GC parameters. The feasibility of GC method was also validated with methodology of statistical analysis and sample analysis.Next, three commonly used edible oils were analyzed as the representative samples to investigate the effect of heating temperature and time on the formation of TFAs, which indicated that the content of TFAs in edible oils increased with the increase of heating temperature and time. In addition, when temperature was higher than180℃, the content of TFAs in edible oils increased significantly with the increase of heating time.Afterwards, the formation of TFAs in edible oils and fried food (chicken fillet and french fries) during deep frying was estimated by a frying model system. Results showed that the composition of fatty acids in both edible oils and food changed significantly after deep frying, but there was no significant difference of TFAs content between different frying cycles.Corn oil was used to investigate the cis-trans isomerization kinetics of unsaturated fatty acids during the heating period with temperature higher than180℃. Results suggested that disappearance of cis-fatty acids corresponded with the kinetics of the first order, while the increase of TFAs followed a zero order reaction. However, it was concluded that heat induced isomerization of unsaturated fatty in a zero order reaction, and the rate constant of isomerization varied according to the Arrhenius law.Finally, α-tocopherol,δ-tocopherol, BHA and BHT were used to study the influence of antioxidants on the formation of TFAs during heating process. The results showed that addition of antioxidant could suppress the formation of TFAs during heating process in some extent, and the relationship between the concentration of8-tocopherol and inhibition ratio suggested that the inhibition ratio increase with the increase of the8-tocopherol concentration.