Study Of The Content Of Trans Fatty Acid During Food Processing

Trans-fatty acids (TFA) is defined as a class of trans double bonds of unsaturated fatty acids, which exists in edible oils or greasy foods. In recent years, the in-depth research of TFA interested researchers at home or abroad extensively, including analysis and formation of TFA and harm to the human body. In this paper, and an effective method of analysis of TFA by GC was established; and we have done a research on the content of TFA in the edible oils during deodorizing temperature and deodorizing time; finally, how the content of TFA is affected by metal ions and foods during frying is studied.The optimal condition of GC with CP-Sil 88 capillary column is as follows:injection port temperature 270℃, split ratio 30:1, flow rate 1.1cm/sec, gas ratio N2:H2:Air =30:45:450, detector temperature 270℃, procedures temperature:45℃heated to 140℃at rate of 8℃/min, heated to 170℃at rate of 6℃/min, heated to 190℃at rate of 6℃/min, kept 20min, then heated to 215℃at the rate of 8℃/min, maintained lOmin. The evaluation methodology of TFA's analysis showed that the retention-time's RSD of 37 kinds of FAME were between 0.0038 and 0.1708; the response-values'RSD of 7 kinds of TFA and FAME in rapeseed oil was in the range of 0.574%-2.886% and 1.672%-5.61% respectively; the T-test of measured value and true value was between 0.5022%-11.77%, T-tests proved no significant difference for most of FAME(a= 0.05), but a small part of FAME which had a greater t-value than the critical should be corrected by correction factors which were listed in the table. The results showed that all FAME had a very good reproducibility of retention-time and responds-value, and we got a reliable determination.Deodorizing temperature at 240℃for the rapeseed oil was a demarcation point to some extent to the formation of TFA; the content of TFA had no significant increase when deodorizing temperature was below 240℃and deodorizing time was less than 70min; TFA increased at 240℃only if the deodorization time was more than 70min; TFA increased with time when deodorizing temperature was higher than 250℃; TFA was in the range of 2%-5.22% in the rapeseed oil. The content of TFA in the cottonseed oil had no change when deodorizing temperature was blow 240℃; TFA increased slowly when deodorizing time was less than 70min; TFA in the cottonseed oil was in the range of 3.57%-7.92%. TFA would be produced in the rapeseed and cottonseed oils during deodorizing process, in which deodorizing temperature had a higher impact on the content of TFA than deodorizing time.The content of TFA increased differently with the concentration of metal ions. TFA increased slowly with the concentration of Fe+, the highest content was 5.5%when the concentration was 3mg/mL, which was 2.77 times of adding no substance; the content of TFA increased significantly with the concentration of Al3+, the highest content was 32.15%when the concentration of Al3+was 3mg/mL, which was nearly 11.58 times of adding no substance. The content of C18:1T increased significantly with the concentration of Al3+, the highest content was 29.32%when the concentration of Al+was 3mg/mL.The content of TFA in the oil had different changes during frying various types of foods. The content of TFA increased significantly when frying pork, butter, suet, and bean curd, of which lard and butter had a higher TFA, was 7.298%and 8.804%respectively; The content of TFA increased when frying carrots, beancurd and suet, which was 1.4 times,2.21 times and 2.59 times of no frying respectively, The content of TFA had no change when frying other foods, such as, leeks, lotus root and potatoes.