I batteri lattici: un parametro di qualità per i formaggi freschi

53 samples of fresh cheese (13 Pasta Filata, 32 fresh cheeses, 4 Mascarpone and 4 Ricotta) were tested by microbiological analyses, according to IDF Standard Methods. A high level of lactic acid bacteria (LAB) was found in the Pasta Filata cheeses, but the Mascarpone and Ricotta cheeses contained virtually no bacteria; The cheeses were classified into 3 groups according to their LAB count and level of contaminants: (a) high level of LAB (>10 6 c.f.u./g) and moderate level of contaminants (<10 4 c.f.u./g); (b) absence of LAB and low level of contaminants (<10 4 c.f.u./g); and (c) absence of LAB and high level of contaminants (>10 4 c.f.u./g). The pH of all cheeses ranged from 4.8-5.2 and the A w from 0.95-0.99. Cheese samples from each of the 3 groups were inoculated separately with Listeria monocytogenes, Salmonella tyhimurium, Staphylococcus aureus, Escherichia coli and Bacillus cereus. The inoculated samples were tested at 1, 7, 14 and 21 days' storage under refrigerated conditions. In type (a) cheese the 5 pathogenic strains, affected by the high level of LAB, decreased rapidly and disappeared within a week. If a large number of LAB were not present, the pathogens, even when initially occurring in limited numbers, could survive for a long time, especially in the presence of a high level of contaminants. It is suggested that the presence of a high content of LAB in cheeses could be used as a quality indicator of whether the designation 'fresh cheese' should be applied.