Thermal Resistance of Two Strains of Listeria Monocytogenes

The thermal resistance of two strains of Listeria monocytogenes, strain NCTC 7973 and NCTC 5105, was demonstrated at five different temperatures (52,57,62,67, 72°C) in pasteurized and whole boiled milk. 3 ml portions of milk suspended at concentrations of ca. 2.23x155 cells ml-1 was heated at temperatures ranging from 52 to 72°C. The D-value of NCTC 7973 for fresh boiled milk ranged from 1620 to 60 sec. In pasteurized milk the D-value was computed ranging from 1860 to 75 sec. Moreover the Z-value for the same strain was 14.2°C and 11.6°C for fresh boiled milk and pasteurized milk respectively. The D-value of strain NCTC 5105 ranged from 1050 to 120 sec. for fresh boiled milk whereas for pasteurized milk it ranged from 2100 to 69 sec. The Z-value of NCTC 5105 was 21.5°C and 13.8°C for fresh boiled milk and pasteurized milk respectively.