Behaviour of Listeria monocytogenes under combined chilling processes
Résumé
The behaviour of Listeria monocytogenes under chilling processes was investigated. Growth kinetics were measured at 7 °C in TSBYE culture medium as a function of pH (7·2 and 6·2), pre-incubation temperatures (4 or 7 °C), cooling (0·05 or 0·1 °C min−1) and freezing (0 and – 5 °C) treatments. Growth curves generated were fitted by Gompertz and Baranyi functions. The Baranyi function gave better parameter estimation values than the Gompertz equation which over-estimated the specific growth rate values. Listeria monocytogenes grew at 7 °C without a lag phase, except when the sub-culture was performed at 37 °C, whereas the specific growth rate was affected by the chilling processes. In fact, L. monocytogenes grew slightly faster at 7 °C when a 4 °C pre-incubation treatment was applied than with a 7 °C pre-incubation treatment. These results suggest that to mimic the processes of contamination in industry, predictive microbiology studies with L. monocytogenes should be performed with organisms cultured at low temperatures.