Survival of listeria monocytogenes in cottage cheese

Samples of cottage cheese known on the Polish market as ,,Grani Quark" were artificially with L. monocytogenes (inoculum 10(3) cells/g). Samples were tested after 0, 2, 5, 7, 10 and 14 days of storage 10 degrees C and after 0 , 2, 3, 4, 7 and 10 days of storage at 20 degrees C. In each sample the pH- value, aerobic plate count number of listeria were determined. It was found that in the samples stored at 10 degrees C the numbers of monocytogenes re mained at a similar level at the beginning of incubation and then decreased . After 14 days storage L. monocytogenes was not detected. In the samples s tored at 20 degrees C, the number of L. systematically decreased during sto rage to an undetectable level found after 10 days. T-4D values (time requir ed for reduction of listeria by 4 log units) were calculated from regressio n analysis and amounted to days for the samples stored at 10 degrees C and 13.3 days for the samples stored at 20 degrees C. These results were to the oretical ones obtained from the Pathogen Modelling Program 4.0. This progra m. enables to predict behavior of L. monocytogenes in culture media. It see ms that the microflora of cottage cheese increases rate of L. monocytogenes dying during storage, particularly at 20 degrees C.