| The polar and non-polar fractions of frying oil were separated using column chromatography. The composition and contents of fatty acids in different fractions were analyzed by GC-MS. The results showed that the polar and non-polar fractions of frying oil had similar composition and relative content of fatty acids. There was extremely significant correlation between the two fractions, including saturated fatty acids (SFA), unsaturated fatty acids (UFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) (r>0.90, p<0.01). The content of cisC18∶?2 in polar fraction was relatively high. The non-polar fraction of frying oil exhibited larger decrease degree in cisC18∶?2/C16∶?0 ratio than polar fraction suggesting the cisC18∶?2 of non-polar fraction had the most intense reaction during the process of generating polar groups. The content of polar compounds in frying oil increased with frying time prolonging. The content of total fatty acids in the polar fraction increased with a gradient, and was significantly correlated with the content of total polar compounds in frying oil (p<0.01). The content of total fatty acids in the non-polar fraction decreased significantly, which indicated that all triacylglycerols were involved in the deterioration reaction during the frying process which led to the increase of the contents of fatty acids with polar groups, and the composition of cisC18∶?2 was closely related to the change of polar fraction content. The classified analysis of complex components of frying oil according to their polarity was beneficial to the comprehensive analysis of the complex components during soybean oil frying, which could provide more reliable data for getting the relationship between fatty acid composition and polar fraction content, and proposing an objective shelf life of frying oil. |
