A predictive model to describe sensitization of heat-treated Bacillus stearothermophilus spores to NaCl

The effect of different concentrations of sodium chloride (NaCl) in the recovery medium on the apparent thermal resistance of Bacillus stearothermophilus spores (strain ATCC 12980) was studied. Spores were heated at different temperatures (115-125 degrees C) and subcultured in medium with different NaCl concentrations [1, 2, 3 and 3.5% (w/v)]. The results indicate that increasing NaCl levels decreases the apparent heat resistance of the spores, over a temperature range of 115-125 degrees C. No significant difference was found between 3 and 3.5% (w/v) NaCl although both reduced B. stearothermophilus heat resistance considerably. A second-order polynomial equation provided a good description of the spores' D value, as influenced by the temperature and NaCl concentration. Predictions from the model compared well with published data, and therefore the model is suitable for predicting the effect of NaCl concentration on thermal inactivation of B. stearothermophilus.