بررسی رفتار لیستریایتوجنز در نوعی پنیر نرم تازه بدون استفاده از مایه لاکتیک متأثر از فاکتورهای سروتیپ باکتری،حرارت و زمان نگهداری

The behavior of L. monocytogenes on fully processed fresh soft (hispanic type) cheese made in laboratory from pasteurized milk was examined, Two strains of L. monocytogenes (Scott A, V7 serotypes 4b and la, respectively) inoculated individually in cheese curd to contain 2x 104/g of samples. The inoculated cheeses incubated at 30,20, 12,8 and 4°C up to 60 days. The chemical analysis revealed 1% salt, 1,8% brine, 53% moisture, 18.7% fat and final pH of 6,6 in cheese samples. Generation time (G) and maximum population levels for both strains were calculated for all storage conditions. The amount of G for strains scott A and V7 at 30,20, 12) 8 and 4°C were (0.81 and 0.89), (1.78 and 1.93), (6.3 and 7.7), (8,49 and 8.23) and (21 and 18.9) hours, respectively. Maximum population levels per gram of samples for strain scott A at 30, 20, 12, 8 and 4°C were> 1.6x 108 after 16 hours, > 1.3× 108 after 73 hours, >1.7×107 after 87 hours, >2.5×107 after 6 days and >2×107 after 19 days of storage respectively, whereas for strain V7 the maximum population levels at similar times of storage were >6.3×lO7, >6.8×lO7, >1.3×l07, 1.4×l07 and2×l07 per gram of cheese samples respectively. The result showed excelent growth of the organism at all storage conditions and since the possibility of Listeria contamination during and after cheese processing is high, therefore, the use of proper antimicrobials in this kind of cheeses seems to be necessary to inhibit the growth of the organism during storage time.