Polymer glass-transition theory was used to gain information about a possible general mechanism to explain the high heat resistance of bacterial spores. In a glassy state the configuration of vital macromolecules and supramolecular assemblies in the spore protoplast would change extremely slowly when heated. The temperature dependence for heat inactivation rates above the glass-transition temperature was shown to be free-volume dependent and described by the kinetics commonly observed for glassy polymers. Glass-transition temperatures for various spores, predicted by nonlinear regression analysis of their heat inactivation rates at different temperatures, increased with increasing heat resistance as expected.
Comparisons of characteristics of recent models and the conventional model of bacterial spore populations during thermal sterilization showed the conventional model was inadequate for general representation because it lacks activation of dormant spores. New models accounting for activation differed in other assumptions but obviated heat shock of indicator spores required when using the conventional model in validations of thermal sterilization. Comparisons of rate constants and simulated and experimental responses of models of B. stearothermophilus spores in constant and dynamic temperatures showed one new model was more general, more accurate and preferred. Arrhenius equations accurately described temperature dependencies of all rate constants of that model.
A mathematical model of Bacillus stearothemophilus spore populations during lethal heating treats activation of dormant spores and inactivation mechanisms affecting dormant/activated spores. Rate constants of activation/inactivation processes were determined from isothermal survivor curves of experiments in 10.5, 110, 115, and 120°C and corresponding simulations with the model. Variations of rate constants with temperature were incorporated by Arrhenius equations responding to general temperature regimes. Tests demonstrated high correspondence between experimental survivor curves and those generated by simulations with the model for isothermal and dynamic, lethal heating. Tests also indicated Arrhenius rate constants at low lethal temperatures (105-120°C) and the model may apply to ultra high temperature. The new model was more effective than the traditional model in representing and predicting spore population dynamics during lethal heating.
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