MODELING THE EFFECTS OF VARIOUS PARAMETERS ON THE GROWTH OF LISTERIA-MONOCYTOGENES ON LIVER PATE

To more fully assess the health hazard posed by Listeria monocytogenes in liver pate products, multi-factorial design experiments were condu cted to examine the influence of temperature (4 and 10 degrees C), NaC l (1 and 3%), sodium nitrite (0 and 200 ppm), sodium erythrobate (0 an d 550 ppm) and spice (0 and 0.4%), on the growth of the organism on ex perimental pate. A total of 16 different liver pate formulations made experimentally were stored at 4 and 10 degrees C for various periods o f time. Analysis of variance was used to determine the effect of the v arious factors on maximum growth rate. L. monocytogenes was able to gr ow well, with temperature being the only factor exerting an effect on the growth rate. After transforming by natural logarithms, analysis of variance of the lag phase gave a more complicated model, but with tem perature again being the only factor demonstrating a main effect. Comp arisons of the experimental data were made against the modelling data from the US Department of Agriculture's Pathogen Modelling Program (PM P). Mean experimental growth rate was significantly lower than the mea n predicted value. Mean experimental lag-phase time was slightly, but not significantly, longer than the mean predicted value. Some formulat ions gave rise to lag-phase times shorter than those predicted by the PMP, a situation which could be hazardous. Additional comparisons done with pate modelling data produced by researchers in New Zealand also showed some discrepancies. Thus, it may not be possible to accurately predict the growth of pathogens on individual foods when using one mod el. (C) 1995 Academic Press Limited