γ-Glutamyl transferase inactivation in milk and cream: A comparative kinetic study

Abstract

The degree and rate of inactivation of γ-glutamyl transferase in raw cow's milk containing two levels of fat (skimmed [0%] and whole [3.5%], and cream [45%]) were measured at different time–temperature combinations in order to evaluate the suitability of this enzyme as a marker for the pasteurization of milk and milk products. A detailed comparative kinetic study of γ-glutamyl transferase inactivation was carried in the temperature range of 60 to 85 °C. Kinetic studies showed that the thermal inactivation of enzyme followed first-order kinetics. The influence of temperature on the inactivation rate constant was quantified using the Arrhenius equation and was characterized by activation energy values of 214.8 ± 4.6, 190.2 ± 3.7 and 174.5 ± 3.5 kJ/mol in skimmed milk, whole milk and cream, respectively. The kinetic data regarding inactivation of milk enzymes can be valuable in terms of implementing food safety management systems, including traceability of the heat treatment step as a critical control point for milk and dairy processes. Heat stability profiles of bovine milk γ-GT were examined with the object of being able to monitor heat treatments slightly or even more severely than typical pasteurization conditions by measurements of residual enzyme activity after heating. Assay procedure was limited to simple colorimetric method that would be most likely to form the basis of a quick, simple and inexpensive test. The importance of this work is related to the possibility of establishing potential markers to evaluate the destruction of the target microorganism associated with each heating process, taking into consideration the safety and quality aspects.