THERMOTOLERANCE OF HEAT-SHOCKED LISTERIA-MONOCYTOGENES IN MILK EXPOSED TO HIGH-TEMPERATURE, SHORT-TIME PASTEURIZATION

The effect of prior heat shock (48-degrees-C for 15 min) on the thermotolerance of Listeria monocytogenes at the minimal high-temperature, short-time (71.7-degrees-C for 15 s) parameters required by the Pasteurized Milk Ordinance was examined. The mean D71.7-degrees-C value for heat-shocked L. monocytogenes was 4.6 +/- 0.5 s (control D = 3.0 +/- 1.0 s); the ratio of D to control D was 1.5. The increased thermotolerance of heat-shocked Listeria cells was not significant and appeared unlikely to have practical implications, in terms of risk assessment, for the safety of pasteurized milk.