Heat resistance kinetics variation among various isolates of Escherichia coli

Abstract

This paper reports an investigation of serotype-specific differences in heat resistance kinetics of clinical and food isolates of Escherichia coli. Heat resistance kinetics for 5 serotypes of E. coli at 60 °C were estimated in beef gravy using a submerged coil heating apparatus. The observed survival curves were sigmoidal and there were significant differences ( p=0.05) of the survival curves among the serotypes. Consequently, a model was developed that accounted for the sigmoidal shape of the survival curves and the serotype effects. Specifically, variance components for serotypes and replicates within serotypes were estimated using mixed effect nonlinear modeling. If it is assumed that the studied serotypes represent a random sample from a population of E. coli strains or serotypes, then, from the derived estimates, probability intervals of the expected lethality for random selected serotypes can be computed. For example, expected serotype-specific lethalities at 60 °C for 10 min are estimated to range between 5 and 9 log 10 with 95% probability. On the other hand, to obtain a 6-log 10 lethality, the expected minutes range, with 95% probability, from 6 to 12 min. The results from this study show that serotypes of E. coli display a wide range of heat resistance with nonlinear survival curves. Industrial relevance This paper is of high current interest since it deals with the ongoing international debate on log linear vs. non-log linear microbial inactivation curves observed during thermal and non-thermal processing. The data on 5 serotypes of E. coli indicate a clear need for further studies with more strains to fully characterize the heat resistance kinetics for E. coli.