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Samples of herring and cod meat exposed to gamma irridiation at a dose of 1.0, 2.5 and 5.0 kGy together with non irridiated meat (control) were stored at 4°C to deter­mine their stability, reduction of the number of psychro- trophic and mesophilic bacteria and to detect the effect of irridiation on the lating quality of meat expressed by sensory evaluation of meat and by peroxide value of muscular fat. It was found that gamma irridiation at the doses 1.0, 2.5 and 5.0 kGy prolonged a mean time of meat storage at 4°C by about 1.8—2.6 days (29—42%) in the case of herrins and by about 1.5—2.3 days (23—35%) in the case of cods. A number of bacteria in the examined samples of meat decreased after irridiation proportionally to the used dose of irridiation. It decreased for psychrotrophic bacteria by about 1—4 log cycles and for mesophilic bacteria by about 1—2 log cycles. The use of the dose of irridiation 2.5 and 5.0 kGy caused a pronounced sensory changes easy to detect during the examination of raw meat, but difficult to detect in cooked meat without seasonings. The intensity of these changes increased with a dose of irridiation and after irridiation with the doses higher than 2.5 kGy a quality of meat is low so that meat can even be degra­ded. The peroxide value in meat of herrings and cods irridiated with 1.0—5.0 kGy increases with the dose of irridiation. On the basis of these data one can conclude that the optimal dose of gamma irridiation of meat of herrings and cods is 2.5 kGy.
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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