Development of twoListeria monocytogenesgrowth models in a meat broth and their application to beef meat

Growth variation ofListeriastrains was taken into account by building two growth models with strains previously characterized, respectively, by their slow (L. monocytogenes CLIP 19532) and fast (L. monocytogenes 14) growth in different conditions of pH, a_wand temperature. Strains of intermediate growth were studied in a meat broth and strains used for the models were grown on the surface of beef meat. Ten growth repetitions at 14°C– a_w0.98–pH 6.2 showed that generation times were similar ratio value (R=standard deviation/average): 3.2%] but that range of lag times was wide (R=27.4%). In broth, calculated lag and generation times were not significantly different between strains from 30 to 14°C, but variations became larger as temperatures came close to 4°C. Model values corresponded well to experimental generation times and to a lesser extent to lag times. On meat at 4°C and 14°C both strains had experimental lag times three-fold longer than predicted lag times. Experimental generation times were shorter than predicted values at 14°C and longer at 4°C: differences between growth in broth and on meat could be due to the characteristics of the meat, the experimental conditions of growth, the mode of inoculation and the way of adjustment of a_w. Growth variations were found between available predictive models.