Study On Fatty Acid Composition And Its Thermal Stability Of Several Chinese Representative Oils

The composition and content of fatty acids vary in the different oils, which will change dramatically after heating. The fatty acid is an important quality indicator of edible oil, the nutritional value of which is closely related to the composition, content, and ratio of the fatty acid. The separation of mixed standard FAME and trans fatty acid methyl ester standards under different chromatographic conditions were compared to select an optimal separation of the chromatographic parameters. In this thesis, a total of141samples of vegetable oil ascribed to11species were collected from10regions and the online stores. The fatty acid composition was analyzed by gas chromatography, and its characteristics were summarized. Meanwhile, the corn oil (rich in n-6fatty acids), the camellia oil (rich in n-9fatty acids), and the flaxseed oil (rich in n-3fatty acids) were selected to be heated. The results were listed as folio wings:1.The baseline of the fatty acid composition can separate under the following chromatographic conditions:CP-sil88capillary column with100mx0.25mm id×0.2μm, the injection port temperature and detector temperature are respectively250℃,260℃;Carrier gas flow rate and column flow rate are68.8mL/min,0.65mL/min respectively, line rate:14.3cm/sec,purge flow rate:3.0mL/min;split ratio:100:1; injection volume:1μl. The method of precision and spiked recoveries experiments met the test requirements, and it fit to detect the fatty acid, especially for the trans fatty acid of the vegetable oil.2. The saturated fatty acid content of peanut oil is18.54g/100g, the highest of the edible oils. The saturated fatty acid contents of rapeseed oil and walnut oil are lower than other vegetable oils, both lower than8g/100g. Camellia oil and olive oil are rich in the monounsaturated fatty acids, the contents of which are78.02g/100g and73.88g/100g respectively. The monounsaturated fatty acids content of walnut oil is7.70g/100g, the lowest. Walnut oil and flaxseed oil are rich in polyunsaturated fatty acids, the contents of which are68.38g/100g,64.37g/100g respectively. The polyunsaturated fatty acids in walnut oil are mainly n-6fatty acids and the content is59.56g/100g. The polyunsaturated fatty acids in linseed oil are mainly n-3fatty acids with the content of47.90g/100g.The trans fatty acids in the olive oil were undetectable, while trace amounts of trans fatty acids were detected in other vegetable oils of the commercially bottled vegetable oils.The fatty acid ratios of different vegetable oils exhibited remarkable differences. The ratios of saturated fatty acid to monounsaturated fatty acid to polyunsaturated fatty acid ratio are in the range of11.5～8.6:0.5～8.9; the ratios of n-6to n-3are in the range of0.3-317.1:1.3. The influence of low-temperature and short-time heating on the vegetable oils is slight, but high-temperature, long-time heating can significantly affect the fatty acid composition and contents in the vegetable oils.At the same heating temperature, the contents of fatty acids in the three oils selected to be heated correlated with heating time.Compared with the unheated samples, the peroxide value, anisidine value, and the total oxidation values of the heated oils increased significantly with heating time extended and the heating temperature promoted.