Studies on the thermal sensitivity of γ-glutamyl transpeptidase measured with a modified test procedure and compared with that of alkaline phosphatase and lactoperoxidase in milk

The milk enzyme gamma-glutamyl transpeptidase (gamma-GT) might be a useful indicator for monitoring the various conditions of milk pasteurisation. In the present work, gamma-GT activity was measured using Clarifying Reagent(R) to facilitate spectrophotometric measurement. The proposed method exhibited a good sensitivity (7.1 mU.mL(-1)) and a satisfying repeatability with a CV of 3% (n = 20). It was well correlated with the reference method for gamma-GT activity measurement in 40 bovine milk samples (r = 0.98). The stability of gamma-GT to milk heat treatments was compared with that of alkaline phosphatase (ALP) and lactoperoxidase. The thermal denaturation characteristics of gamma-GT were very close to those of lactoperoxidase. gamma-GT and ALP were of interest to control the label made from raw milk in Camembert cheese. This method could be suitable for routine quality control and assessment of mild heat treatment.