Samples of cottage cheese known on the Polish market as „Grani Quark” were artificially contaminated with L. monocytogenes (inoculum 103 cells/g). Samples were tested after 0,2,5,7,10 and 14 days of storage at 10°C and after 0,2,3,4,7 and 10 days of storage at 20°C. In each sample the pH-value, aerobic plate count and number of listeria were determined. It was found that in the samples stored at 10°C the numbers of L. monocytogenes remained at a similar level at the beginning of incubation and then decreased. After 14 days of storage L. monocytogenes was not detected. In the samples stored at 20°C, the number of L. monocytogenes systematically decreased during storage to an undetectable level found after 10 days. T-4D values (time required for reduction of listeria by 4 log units) were calculated from regression analysis and amounted to 26.9 days for the samples stored at 10°C and 13.3 days for the samples stored at 20°C. These results were compared to theoretical ones obtained from the Pathogen Modelling Program 4.0. This program enables to predict the behaviour of L. monocytogenes in culture media. It seems that the microflora of cottage cheese increases the rate of L. monocytogenes dying during storage, particularly at 20°C.
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