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 milk were measured in relation to the process of heating to determine the value of these enzymes as markers for the evaluation of milk pasteurization. The activities of the enzymes alkaline phosphatase (ALP), lactic dehydrogenase (LDH), gamma-glutamyltransferase (GGT), and aspartate aminotransferase (AST) 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). Heating the milk at 50 degrees C for 1 to 30 min resulted in no effect on the activity of any of the enzymes. At 60 degrees C, ALP showed the highest sensitivity to heat inactivation, whereas all other enzymes showed resistance. At 70 degrees C, ALP activity was abolished completely after 1 min, whereas GGT and LDH lost most activity after 10 min, and AST still maintained 50% activity even after 30 min. At 80 degrees C, the activities of LDH and GGT were lost, whereas AST still 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 the highest.