Estimation of Chemical Properties and Color Changes of Frying Oil Used on a Large Scale

Objective: The objective of this study was to estimate the basic chemical properties of oil used for deep-frying on a large scale and to investigate a facile method for screening deteriorated oil. Method: Chemical properties and color of oil used repeatedly for deep-frying in one of our campus restaurants were determined. Result: Acid value (AV) of oil used for 3 h per day for 9 days in the campus restaurant remained within safe limits in accordance with the Food Sanitation Act. Carbonyl value (COV), polar compound (PC) and triacylglycerol (TG) contents, and Gardner color of the oil were in the ranges 2~10, 5%~18%, 90%~98.5% and 1~12, respectively. Gardner color showed good correlation with AV, COV, and PC content, but TG content showed poor correlation with AV, COV, PC content, and Gardner color. Conclusion: Because of the good correlations among Gardner color and AV, COV, and PC content of the oil, we concluded that determination of Gardner color—which is very easy and inexpensive—was a facile method for assessing the deterioration of oil used in deep-frying.