| Trans fatty acids (TFA) are fatty acids containing at least one trans double bond; but only polyunsaturated fatty acids with methylene interrupted double bonds. TFA with C-(18) structure is most commonly seen among all fatty food. Too much intake of trans fatty acids is harmful for human body. Such as impacting digestion and absorption of essential fatty acids, leading to occurrence of cardiovascular disease, causing brain function decline. The contents of trans fatty acids in food have already been restricted in some countries recently. At present, we have not set related regulations for TFA in foods in our country. Current researches on trans fatty acids were mainly focused on the detection method and the impact on human health. However, the risk assessment of TFA have few been studied, and little attention was paid on estimating dietary intake of TFA of adolescents. In our country, there are differences of food structure among different groups of people. Thus, study on TFA intake among adolescents has more practical significance.In this study, the detection objects were that the trans-palmitelaidic(9t-C16:1), the trans-elaidic(9t-C18:1) and the trans-vaccenic(11t-C18:1) which are most commonly seen in foods. A fast and effective GC-MS method for analysis of trans fatty acids was established. Using the developed detection method, the trans fatty acids in some edible oils and oil foods were detected. Various universities, primary schools and secondary schools in baoding were randomly selected to collect samples. Students (the total number of which is 1564) of the chosen schools were selected as interviewers to participate in the dietary survey. The purpose was to assess the exposure level of TFA among adolescents in medium-sized cities in China.The main results are summarized as follows:1. The conditions of trans fatty acids methyl esterification were optimized. With peak area of trans fatty acids in the sample of hydrogenated soybean oil as an indicators for the assessment, through the single factor experiment and the orthogonal experimental design, the volume of the esterification reagents, methyl esterifacation temperature and methyl esterifacation time had been compared to evaluate the influences of the three factors for methyl esterification. The best methyl esterification conditions of the trans fatty acids were designated at the final. They were that the volume of the esterification reagents of 4 mL, methyl esterifacation temperature of 50℃, methyl esterifacation time of 30 min. 2. A GC-MS method for determination of 9t-C16:1, 9t-C18:1 and 11t-C18:1 in foods was established. In the present study, it was found experimentally that the optimal GC conditions are as follows: HP-INNOWAX capillary column (30 m×0.25 mm×0.25μm), sampler temperature: 250℃, detector temperature: 230℃, pure helium as carrier gas, flow rate: 0.6 mL/min, split injection mode with the split ratio of 50:1 and tail-blows rate 20 mL/min. Calefactive program of column is as follow: the column temperature was set at 150℃, then increased at 20℃/min to 190℃(hold 2 min), at last raised 1℃/min until 200℃(hold 5 min), and injector volume is 1μL. Trans-palmitelaidic acid,trans 9-elaidica cid and 11-vaccenic acid can be separated completely within 20 min under these operation conditions. And the linear scope was from 0.02 mg/mL to 0.3 mg/mL (r>0.9991). The detection limits of the three trans fatty acid respectively were 5.36μg/mL, 4.80μg/mL and 4.13μg/mL. The recovery rate was between 86.4% and 94.9% with the relative standard deviation was between 1.02% and 3.91%.3. By the developed detection method of trans fatty acids, the trans fatty acids contents in edible oil and oil-containing foods were investigated. The results showed that the TFA average mean of all vegetable oils analyzed was 0.79%. The contents of the TFA in the refined oils were as follows: peanut oil 0.33% - 0.64%, soybean oil 0.39% - 0.71%, rapeseed oil 0.58% - 0.67%, maize oil 1.08%, sunflower seed oil 0.58%, salad oil 1.04%, grain cooking oil 0.93%, sesame oil and 0.34%, cottonseed oil 3.25%. The contents of TFA in various oil-containing foodstuffs were remarkably different: sandwich biscuits(2%~); wafer, cookies and potato chips (~1%); Because of the wide use of edible oils and high temperature of frying and baking, some traditional processed foods (such as deep-fried twisted dough sticks)are high in TFA, the highest was 8.08%. While contents in some fried foods, such as fried chicken and deep-fried twisted dough sticks (1%~9%) changed notably, depending on oil categories and total frying time.4. The average intake of dietary intake of adolescents was 2.22 g/d. The average intake of primary school students was the highest; it was up to 3.42 g/d (boys 3.71 g/d and girls 3.14 g/d), which was higher than international standards of WHO/FAO for 2 g/d. The average intake of junior high school students was 2.47 g/d (boys 2.47 g/d and girls 1.78 g/d). The average intake of high school students was 1.96 g/d (boys 2.07 g/d and girls 1.84 g/d). The average intake of university students was 1.36 g/d (boys 1.23 g/d and girls 1.49g/d). |
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