Predictive model to describe the combined effect of pH and NaCl on apparent heat resistance of Bacillus stearothermophilus

The combined effect of pH and NaCl on the apparent thermal resistance of Bacillus stearothermophilus ATCC 12980 spores was studied. Spores were heated at different temperatures (115–125°C) in mushroom substrate, acidified using glucono-δ-lactone to different pH levels (from 5.75 to 6.7), which contained concentrations of NaCl that ranged from 0.5 to 3% (w/v). The recovery medium was acidified to the same pH level and contained the same NaCl concentration as the heating menstruum. A factorial experimental design allowed a predictive model to be developed, which described the combined effect of heating temperature, pH and NaCl on the thermal resistance of B. stearothermophilus spores. Predictions from the model provided a valid description of the data used to generate the model, and agreed with observations from the literature and from an independent experiment performed using asparagus and bean substrates.