BEHAVIOR OF STAPHYLOCOCCUS-AUREUS AND OF ESCHERICHIA-COLI AND INJURY FORMATION DURING PRODUCTION AND STORAGE PHASES OF PARMESAN CHEESE

The behaviour of S. aureus and E. coli during production and storage p hases of Parmesan cheese was studied. The product was prepared followi ng the usual technology, being the milk used inoculated with S. aureus ATCC 25923 and E. coli ATCC 25922, after pasteurization, to provide c oncentrations of approximately 10(6) and 10(7) cells/ml, respectively. Cheese pieces were kept at 15 +/- 21-degrees-C for 130 days and later at 21 +/- 2-degrees-C until day 200. In order to assess injury format ion, counts were made on all of the samples of S. aureus and E. coli, both by traditional methodology and those employing the recovery perio d of stressed cells (15). pH and acidity were constantly determined. T he ripening process of Parmesan cheese prompted the reduction of four log cycles on S. aureus counts. In the case of E. coli the multiplicat ion occurred at the beginning of ripening (about one log cycle), which stabilized later on, with a count decrease to four and five log cycle s in relation to the beginning of ripening. Thermal injury occurred on both organisms during heating phase of curd at 50-degrees-C, especial ly on E. coli. Sublethal acid injury on E. coli began to occur faster and in smaller concentrations of lactic acid (0,50%) than it did for S . aureus (0,70%), during ripening.