Buffalo-milk enzyme levels, their sensitivity to heat inactivation, and their possible use as markers for pasteurization

The activities and rates of inactivation of four enzymes in raw buffalo mil k were measured in relation to the process of heating to determine the valu e of these enzymes as markers for the evaluation of milk pasteurization. Th e activities of the enzymes alkaline phosphatase (ALP), lactic dehydrogenas e (LDH), gamma-glutamyltransferase (GGT), and aspartate aminotransferase (A ST) were measured before and after heating at 50, 60, 70, and 80 degrees C for 1, 3, 5, 10, 20, and 30 min. The enzyme GGT showed the highest activity (712 +/- 601 IU/liter), followed by LDH (386 +/- 183 IU/liter), ALP (295 /- 164 IU/liter), and AST (18 +/- 4 IU/liter). Beating the milk at 50 degre es C for 1 to 30 min resulted in no effect on the activity of any of the en zymes. At 60 degrees C, ALP showed the highest sensitivity to heat inactiva tion, whereas all other enzymes showed resistance. At 70 degrees C, ALP act ivity was abolished completely after 1 min, whereas GGT and LDH lost most a ctivity after 10 min, and AST still maintained 50% activity even after 30 m in. At 80 degrees C, the activities of LDH and GGT were lost, whereas AST s till retained some of its activity. The results suggest that in addition to ALP, LDH and GGT, but not AST, are potential markers for heat denaturation in buffalo milk, with GGT having the advantage that its concentration is t he highest.