Physicochemical Properties and Oxidative Stability of Vegetable Oils during Repeated Frying of Potato Chips

Abstract

Deep-fat frying is a widely used cooking method to make fried products with savory flavor and desirable texture. Although frying temperature, frying time, antioxidant content, and fatty acid composition have been reported to be factors that can affect the chemical reactions during frying process, fatty acid composition of a frying oil is the most important variable for its quality. Commercial frying oil is generally repeatedly used in frying. However, oxidative stability and volatile compounds of repeatedly used frying oils with different fatty acid compositions and antioxidant contents have been little studied. Therefore, it is necessary to study the changes in physicochemical properties, oxidative stability, and volatile compounds of repeatedly used frying oils with different fatty acid compositions. Thus, physicochemical properties and oxidative stability of refined coconut oil (RCO), refined soybean oil (SBO), pure olive oil (POO), and vegetable shortening (VST) during repeated frying of potato chips were determined in this study. Potato chips were fried in an oil for 4 min at 180±5°C. After the chips were taken out, the oil was heated for 2 min for the next frying. This process was repeated with 80 cycles. The oils were collected at every 20th cycle. Changes in fatty acid composition, total phenolic contents, tocopherols, DPPH radical scavenging activity, color (Hunter L*, a*, and b*), peroxide value (PV), acid value (AV), conjugated dienes (CD), total polar compounds (TPC), p-anisidine value (p-AN), and volatile compounds of the oils were monitored. Polyunsaturated fatty acids of the tested oils significantly decreased after frying (P<0.05). SBO among the tested oils was the highest in tocopherols, followed by POO and VST, while they were not detected in RCO. Tocopherols in SBO, POO and VST, and DPPH radical scavenging activities of POO and VST significantly decreased after frying (P<0.05). Significantly strong correlations between total tocopherol contents and DPPH radical scavenging activities of POO and VST were observed (P<0.01). L* values of the oils significantly decreased, and a* and b* values significantly increased after frying (P<0.05). AV, CD, TPC, and p-AN of the oils significantly increased after frying (P<0.05). RCO, which has a high level of saturated fatty acids, seemed to be the most stable among the tested oils, considering the levels of CD and p-AN. Volatile compounds in the oils significantly increased after frying (P<0.05). Compositions and contents of alkanals, 2-alkenals, and 2,4-alkadienals in the oils during frying were affected by their fatty acid compositions. In conclusion, fatty acid composition and tocopherol content of frying oils may be important factors that significantly affect physicochemical properties, oxidative stability, and levels and compositions of volatile compounds in repeatedly used oils.