Formation and Inhibition of Cholesterol Oxidation Products during Marinating of Pig Feet

Cholesterol oxidation products (COPs), formed during the heating of cholesterol-rich foods, have been shown to cause cancer and coronary heart disease. The objectives of this study were to develop a GC-MS method for the determination of COPs in pig feet meat, skin, and juice during marinating and to study the formation and inhibition of COPs as affected by the incorporation of soy sauce and sugar. Results showed that an HP-SMS column could provide an adequate separation of cholesterol, 5 alpha-cholestane (internal standard), and seven COPs, including 7 alpha-OH, 7 beta-OH, 5,6 beta-OH, 5,6 alpha-OH, triol, 25-OH, and 7-keto, within 15 min with a temperature-programming method. Most COPs in pig feet meat were generated at a larger amount than in pig feet skin and marinating juice over a 24 h heating period at about 100 degrees C. The Maillard browning index rose with increasing heating time, whereas the pH showed a slight change in marinated juice. Both reducing sugar and free amino acid contributed to the formation of Mallard reaction products. The incorporation of soy sauce and crystal sugar into fresh juice was effective in inhibiting COPs formation in pig feet, skin, and juice over a 30 min preheating period.