Kinetics of forming polar compounds in frying oils under frying practice of fast food restaurants

The aim of the present work was to study the kinetics of polar compounds in the fast food restaurant frying systems. A modified kinetic equation was proposed, which revealed that the deterioration kinetics (total polar compounds (TPC)) were inconsistent for fifteen different frying systems. The contents of TPC, oxidized triacylglycerol oligomers (TGO) and oxidized triacylglycerol dimers (TGD) showed a decelerating increase tendency, while the values of diacylglycerols (DG) and free fatty acids (FFA) linearly increased with frying time. In contrast, the result of oxidized triacylglycerol (OTG) rose first and then dropped gradually. Results of Pearson correlation analysis further exhibited that positive correlations among most of the polar compounds contents (R = 0.390–0.912, p < 0.01) were pointed out, and the TPC content was significantly correlated with the contents of TGD (R = 0.912, p < 0.01) and TGO (R = 0.955, p < 0.01), as well as the logarithm of DG content (R = 0.874, p < 0.01) and FFA content (R = 0.899, p < 0.01). Therefore, the TGD, TGO, DG and FFA are possible to be predicted by measuring the TPC content during restaurant frying. These findings will be very helpful to predict and control the oils deterioration during fast food restaurant frying.