DEVELOPMENT OF 2 LISTERIA-MONOCYTOGENES GROWTH-MODELS IN A MEAT BROTHAND THEIR APPLICATION TO BEEF MEAL

Growth variation of Listeria strains was taken into account by buildin g two growth models with strains previously characterized, respectivel y, by their slow (L. monocytogenes CLIP 19532) and fast (L, monocytoge nes 14) growth in different conditions of pH, a, and temperature. Stra ins of intermediate growth were studied in a meat broth and strains us ed for the models were grown on the surface of beef meat. Ten growth r epetitions at 14 degrees C-a(w) 0.98-pH6.2 showed that generation time s 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 a nd generation times were not significantly different between strains f rom 30 to 14 degrees C, but variations became larger as temperatures c ame close to 4 degrees C. Model values corresponded well to experiment al generation times and to a lesser extent to lag times. On meat at 4 degrees C and 14 degrees C both strains had experimental lag times thr ee-fold longer than predicted lag times. Experimental generation times were shorter than predicted values at 14 degrees C and longer at 4 de grees C: differences between growth in broth and on meat could be due to the characteristics of the meat, the experimental conditions of gro wth, the mode of inoculation and the way of adjustment of a(w). Growth variations were found between available predictive models. (C) 1998 A cademic Press.