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 concentration on the growth dynamics of Enterococcus faecalis EF37, its proteolytic activity and its production of biogenic amines have been studied. The effects of the selected variables have been analysed using a Central Composite Design. The production of biogenic amines, under the adopted conditions, was found to be mainly dependent on the extent of growth of E. faecalis. Its proteolytic activity was not a limiting factor for the final amine production, because in the system studied (skim milk) an excess of precursors was guaranteed. Quantitatively, the most important biogenic amine produced was 2-phenylethylamine but substantial amounts of tyramine were detected in all the samples. This work confirms that the main biological feature influencing the biogenic amine formation is the extent of growth of microorganisms, like E. faecalis, characterised by decarboxylase activity. In the traditional and artisanal cheeses produced using raw milk, enterococci usually reach levels of 10(7) cells/g. With this perspective, it is important that the presence of biogenic amines due to the activities of these microorganisms is maintained within safe levels, without affecting the positive effects of enterococci on the final organoleptic characteristics of the cheese.