A Novel Evaluation Index for Predicting the Degradation Rate of Frying Oils Based on Their Fatty Acid Composition

The changes in the fatty acid composition of eleven edible oils (soybean, rapeseed, natural and refined sesame, corn, safflower, olive, rice bran, natural and refined perilla, coconut) are investigated during deep frying. French fries are intermittently fried for 5 h each day for 6 consecutive days at 180 °C in these oils. The results suggested that all of the oils contained large amounts of unsaturated fatty acids (83.49–95.28%) before deep frying, except for coconut oil (7.13%). With the extension of frying time, the content of unsaturated fatty acids in the oils decreased linearly (Y = −AT + 100, R² = 0.955–0.990) except in the coconut oil. The equation (A = 0.113X + 0.203, R = 0.836) can be used to determine the decomposition rate of unsaturated fatty acids (A) in a variety of unsaturated fatty acid‐based oils. The ratio of palmitic acid to oleic acid in the oils before deep frying (X) has an important impact on the degradation of a variety of unsaturated fatty acid‐based oils, and can be used as an evaluation index for predicting the degradation rate of such oils before deep frying. Practical Applications: Changes to the unsaturated fatty acid content of a variety of unsaturated fatty acid‐based oils during deep frying can be predicted using this novel evaluation index. A clear understanding of the deterioration process of frying oils can be obtained when the index is combined with other indicators of deterioration. The index can facilitate timely judgments to prevent the over‐use of frying oils according to the waste oil standards of individual countries. This would maximize the utilization of oil while reducing the production of substances that are harmful to the human body. With the extension of frying time, the content of unsaturated fatty acids in the oils decreased linearly (Y = −AT + 100). The equation (A = 0.113X + 0.203) can be use to determine the decomposition rate of unsaturated fatty acids in a variety of unsaturated fatty acid‐based oils. X is the ratio of palmitic acid to oleic acid in the oils before deep frying, and can be use as an evaluation index for predicting the degradation rate of a variety of unsaturated fatty acid‐based oils before deep frying.