THERMAL INACTIVATION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE AND ENTEROCOCCUS-FAECIUM IN MILK-BASED SYSTEMS

Untreated whole milk, skim milk, sweetened milks, sweetened and unswee tened creams and ice-cream mixes were preincubated with a culture of E nterococcus faecium, then subjected to heat treatment in a pilot-scale plate heat exchanger using a hold of 15s at 78 degrees C. The liquids were examined for gamma-glutamyltranspeptidase (GGTP) activity and to tal streptococcal count before and after heat treatment and the result s plotted against water activity (a(w)). There was a good correlation between reduction in GGTP activity, destruction of streptococci and a( w), demonstrating the potential of the enzymic assay for assessing the severity of HTST heat treatments above the minimum for pasteurization .