Quantitative description of Listeria monocytogenes inactivation kinetics with temperature and water activity as the influencing factors; model prediction and methodological validation on dynamic data

The microbial evolution in foods over time is governed by process and storage conditions, and product characteristics. Mathematical models that accommodate the effect of both process temperature and product water activity on the microbial inactivation are studied in this research. Explicitly, models based on Arrhenius, response surface and Bigelow type relationships are developed and evaluated. The Bigelow type model revealed to be the most suitable. Experiments with macerated potato inoculated with Listeria monocytogenes were used to estimate associated inactivation parameters. The inactivation parameters, Asym D60 = 1.79 min, z = 7.11° and zaw = 0.23 were estimated and could be interpreted microbiologically. The parameter estimation step of the selected model was further developed by adding to it a bias factor and incorporating more microbiological information. At a final step, the complete identified model was used to predict the inactivation kinetics of L. monocytogenes under surface dry heating conditions at holding temperatures of 90 and 100 °C and lowering aw values. The confrontation of model predictions with the corresponding dynamic experimental data worked as a validation step. In summary, the induced heat resistance of L. monocytogenes due to the decreasing aw is an important microbiological phenomenon expressed through the estimation of the inactivation parameter zaw.