Modelling the effects of various parameters on the growth of Listeria monocytogenes on liver pâté

Abstract

To more fully assess the health hazard posed by Listeria monocytogenes in liver pâté products, multi-factorial design experiments were conducted to examine the influence of temperature (4 and 10°C), NaCl (1 and 3%), sodium nitrite (0 and 200 ppm), sodium erythrobate (0 and 550 ppm) and spice (0 and 0·4%), on the growth of the organism on experimental pâté. A total of 16 different liver pâté formulations made experimentally were stored at 4 and 10°C for various periods of time. Analysis of variance was used to determine the effect of the various factors on maximum growth rate. L. monocytogenes was able to grow 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 temperature again being the only factor demonstrating a main effect. Comparisons of the experimental data were made against the modelling data from the US Department of Agriculture's Pathogen Modelling Program (PMP). Mean experimental growth rate was significantly lower than the mean predicted value. Mean experimental lag-phase time was slightly, but not significantly, longer than the mean predicted value. Some formulations gave rise to lag-phase times shorter than those predicted by the PMP, a situation which could be hazardous. Additional comparisons done with pâté 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 model.