Effects of pH, temperature and NaCl concentration on the growth kinetics, proteolytic activity and biogenic amine production of Enterococcus faecalis

In this work, the combined effects of temperature, pH and NaCl concentratio n on the growth dynamics of Enterococcus faecalis EF37, its proteolytic act ivity and its production of biogenic amines have been studied. The effects of the selected variables have been analysed using a Central Composite Desi gn, The production of biogenic amines, under the adopted conditions, was fo und to be mainly dependent on the extent of growth of E. faecalis. Its prot eolytic activity was not a limiting factor for the final amine production, because in the system studied (skim milk) an excess of precursors was guara nteed. Quantitatively, the most important biogenic amine produced was 2-phe nylethylamine but substantial amounts of tyramine were detected in all the samples. This work confirms that the main biological feature influencing th e biogenic amine formation is the extent of growth of microorganisms, like E. faecalis. characterised by decarboxylase activity. In the traditional an d artisanal cheeses produced using raw milk, enterococci usually reach leve ls of 10(7) cells/g. With this perspective, it is important that the presen ce of biogenic amines due to the activities of these microorganisms is main tained within safe levels, without affecting the positive effects of entero cocci on the final organoleptic characteristics of the cheese. (C) 2001 Els evier Science B.V. All rights reserved.