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

Abstract

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.

Response to the Letter to the Editor Regarding “A Novel Evaluation Index for Predicting the Degradation Rate of Frying Oils Based on their Fatty Acid Composition”

“…His research was all carried out at 120 °C with an automatic Rancimat apparatus, which was close to theoretical autoxidation experimental conditions. Different from his research, our research was conducted under real frying conditions at 180 °C, which was very close to the actual frying process in life. It is acceptable if the results are different due to different experimental conditions.…”

“…We thank Dr. Albert Dijkstra (the author of the preceding Letter to the Editor) for his interest in the publication “A Novel Evaluation Index for Predicting the Degradation Rate of Frying Oils Based on Their Fatty Acid Composition,” which developed a novel index to predict the unsaturated fatty acid degradation rate of a variety of unsaturated fatty acid‐based oils during deep frying.…”

Simplicity is a Worthwhile Goal but Does Not Always Provide the Correct Answer

“…It would enable users to choose the most stable frying oils and guide producers in their development of more stable oils. It is therefore with great interest that I studied the article by Liu et al because it claims to provide a novel evaluation index for frying oils that only takes their fatty acid composition into account. Another reason that I studied the article with great interest is that some 20‐odd years ago, I wrote a paper that also correlates the stability of an oil to its fatty acid composition.…”

“…Liu et al . on the other hand concluded that “the ratio of palmitic to oleic acid in the oils before deep frying 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.” Now, it could be that this ratio is a roundabout way of expressing the polyunsaturated content of the various oils, but studying the paper by Liu et al.…”

“…In summary, Liu et al . aimed at arriving at a simple expression to correlate oil composition with oil deterioration, which is a worthy endeavour, but they oversimplified by not taking the antioxidant content of their oils into account.…”