Microbial dynamics versus mathematical model dynamics: The case of microbial heat resistance induction

Abstract

Quantifying the microbial inactivation during a thermal treatment is a main objective in the food industry in order to design a microbiologically safe process and to avoid fail-dangerous or, on the contrary, overly conservative heat processes. This work focuses on the effect of different heating regimes, i.e., with a heating rate of 0.15, 0.20, 0.40, 0.55, 0.82, and 1.64 °C/min, from 30 to 55 °C, on the (induced) heat resistance of Escherichia coli K12 MG1655. Dynamic inactivation experiments performed under realistic time–temperature conditions are used as a vehicle to validate pertinent modelling and microbial information originating from static inactivation experiments and comprehensive literature observations. The influence of the thermal process conditions on the microbial heat resistance is verified based on a working hypothesis for the performed microbial predictions. Microbial heat resistance is utmost perceived in the lowest heating rates considered (with a corresponding come-up time higher than 30.61 min). Thermal inactivation of microorganisms in foods has been used and optimized effectively since centuries. However, even more recent developments such as the D-value concept are based on the assumption that the heat resistance of microorganisms measured under isothermal conditions is constant and also applicable to foods heated and cooled relatively slow. This highly relevant paper is based on the hypothesis that heating rates during processing can be an essential factor for heat resistance adaption of microorganisms (using E. coli as a model) and uses a dynamic microbial modelling approach for considering microbial adaptive responses. This approach is an important step towards avoiding process induced adaptive responses allowing pathogenic microorganisms to persist during storage of foods.