Thermal resistance of Listeria monocytogenes.

Two methods were used to study the thermal resistance of Listeria monocytogenes. The D60 degrees C values ranged from 1.3-6.5 min in an open vessel. D72 degrees C varied from 0.06-1.5 s and z from 3.1-6.5 K (38 strains) in capillary tubes. Therefore a conventional pasteurization process of 15 s at 72 degrees C could assure 10-750 decimal reductions, depending on the strain. Six days enrichment, at 4 degrees C in milk prior to incubation at 37 degrees C, did not show any influence on measured heat resistance (4 strains). A significant difference in thermal resistance among strains according to their serotype was noted: strains belonging to serogroup 1 were more heat resistant than those belonging to serogroup 4.