GAMMA-GLUTAMYL-TRANSFERASE AS A MARKER FOR THE PASTEURIZATION OF RAW-MILK

The degree and rate of inactivation of gamma-glutamyltransferase in ra w cow's milk by heating at 50, 60, 70, and 80 degrees C for 1, 2, 3, 5 , 10, 15, 20, 25, and 30 min were measured to evaluate the suitability of this enzyme as a marker for the pasteurization of milk. The enzyme s alkaline phosphatase and lactate dehydrogenase were also measured un der similar conditions for comparison. The patterns of heat inactivati on of gamma-glutamyltransferase and alkaline phosphatase were similar, with only a minimal inactivation of the enzymes at 50 degrees C. The rate of inactivation increased as a result of increasing temperatures and time. A complete inactivation of both enzymes was seen at 70 degre es C after 10 min and at 80 degrees C after 1 min. Lactate dehydrogena se showed a higher heat resistance with almost complete inactivation a t 70 degrees C for 30 min, and compete: inactivation at 80 degrees C f or 3 min. No activities of these enzymes were found in commercially pa steurized or heat-treated milk. The levels of gamma-glutamyltransferas e in raw milk were between 8 and 10% higher than those of alkaline pho sphatase and lactate dehydrogenase, making it more sensitive and accur ate as a testing marker. It seems that gamma-glutamyltransferase may s erve as a good pasteurization marker. Furthermore, the simplicity of t esting and the availability of commercial bits for testing by both wet and dry chemistry make it an attractive choice, especially because dr y chemistry procedures overcome the difficulties originating from the turbidity of milk, which interferes with spectrophotometric procedures .