Objective An experimental method was established to determine the level of trans-fatty acids in edible vegetable oil and the changes of trans-fatty acid content during high-temperature simulated cooking.
Methods Four common edible vegetable oils on the market were selected， and three temperature points were set at 180 ℃ （light stir-fry）， 220 ℃ （fry） and 260 ℃ （stir fry）. The samples were taken after the heat treatment of 0， 1， 2， 3， 4， 5， 6 and 7 hours，respectively， to investigate the changes of trans-fatty acid content.
Results Under the heat treatment of 180 ℃ and 220 ℃， the content of trans-fatty acids remained basically stable in rapeseed oil， corn oil， soybean oil and olive oil. Under the heating condition of 260 ℃， the content of trans-fatty acids in these four vegetable oils increased significantly， and the absolute content of trans-fatty acids in rapeseed oil was the highest， reaching 6.84%. Soybean oil showed the larger increase， up to 247.90% from the initial content. The content of trans-fatty acids in olive oil increased from 0.26% to 1.69%， although the increase was large， but the absolute content of trans-fatty acids was still low. The content of trans-fatty acids in sesame oil increased significantly under the three temperatures， reaching 4.79% when heated at 260 ℃， and an increase of 369.61% compared with no heating.
Conclusion Trans-fatty acid content in edible vegetable oils increases significantly in the cooking process， the higher the temperature and the longer the cooking time， the more significant the increase. It is recommended to avoid high temperature cooking and long time fried food.
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