As already observed in MCT I, the behaviour of L. monocytogenes during storage at 4 C also depended both on the level of
contamination and on the type of cheese. Growth of pathogens in cheese is controlled by several preservation factors, such as pH, aw, salt content, and O2 concentration (Papageorgiou & Marth,1989). In mould-ripened cheeses most of these factors change during ripening. In particular, proteolysis of casein results in the release of ammonia and utilisation of lactic acid, with a consequent increase in pH that contributes to creating favourable conditions for growth
(Gobbetti et al., 1997). Moreover, it has been suggested that high salt concentrations and the presence of free fatty acids could inhibit the multiplication of L. monocytogenes during the ripening of blueveined cheeses (Papageorgiou & Marth,1989). The high NaCl percentage, the low aw and the low moisture content of PG, compared to SG, could be correlated with the greater inhibition of the growth of L. monocytogenes.