Thermal inactivation of gamma-glutamyltranspeptidase and Enterococcus faecium in milk-based systems

Untreated whole milk, skim milk, sweetened milks, sweetened and unsweetened creams and ice-cream mixes were preincubated with a culture of Enterococcus faecium, then subjected to heat treatment in a pilot-scale plate heat exchanger using a hold of 15 s at 76 degrees C. The liquids were examined for gamma-glutamyltranspeptidase (GGTP) activity and total streptococcal count before and after heat treatment and the results plotted against water activity (aW). There was a good correlation between reduction in GGTP activity, destruction of streptococci and aW, demonstrating the potential of the enzymic assay for assessing the severity of HTST heat treatments above the minimum for pasteurization.