Kinetics of thermal destruction of Bacillus stearothermophilus spores using a two reaction model

A short review of mathematical procedures developed to analyse bacterial spores thermal destruction dynamics has enabled us to propose a classification for them, depending upon how they are founded experimental observations. The observation of two states (dormant and activated spores) and two transitions (activation of dormant spores and destruction of activated spores) was considered to be the maximum but prudent qualitative interpretability of data reported in papers. Basic models whose formulation was considered to be based on hypotheses well supported experimentally (single first order destruction or simultaneous first order activation of dormant spores and first order destruction of activated spores) were tested in order to predict the non-isothermal spore population dynamics of Bacillus stearothermophilus. Isothermal treatment of spores suspended in water showed, early in the treatment, a typical large population increase associated with the activation phenomenon (80 to 90% of spores were found to be dormant). The non-isothermal treatment was performed to come close to a can cold spot temperature history. The single first order reaction was unsuitble for characterizing the spore crop studied. The two reaction model was shown to be appropriate for developing advanced procedures for sub-UHT process design.