Kinetic model for studying the effect of quercetin on cholesterol oxidation during heating.

Inhibition of the heat-induced cholesterol oxidation at 150 degrees C by incorporation of quercetin was kinetically studied. Results showed that without quercetin, the cholesterol oxidation products (COPs) concentration increased with increasing heating time. A low amount (0.002%, w/w) of quercetin was effective in inhibiting the formation of COPs during the initial heating period (< or =30 min) at 150 degrees C. However, after prolonged heating (30-120 min), a low antioxidant activity was observed because of the degradation of quercetin. When using nonlinear regression models for kinetic study of cholesterol oxidation in the absence of quercetin, the epoxidation showed the highest rate constant (h(-1) = 683.1), followed by free radical chain reaction (h(-1) = 453.5), reduction (h(-1) = 290.3), dehydration (h(-1) = 155.5), triol dehydrogenation (h(-1) = 5.35), dehydrogenation (h(-1) = 0.68), thermal degradation (h(-1) = 0.66), and triol formation (h(-1) = 0.38). However, in the presence of quercetin, the reaction rate constants (h(-1)) for epoxidation (551.4), free radical chain reaction (111.7), and thermal degradation (0.28) were reduced greatly. The kinetic model developed in this study can be used to predict the inhibition of COPs by quercetin during the heating of cholesterol.