Modeling the Recovery of Heat-Treated Bacillus licheniformis Ad978 and Bacillus weihenstephanensis KBAB4 Spores at Suboptimal Temperature and pH Using Growth Limits

Abstract

ABSTRACTThe apparent heat resistance of spores ofBacillus weihenstephanensisandBacillus licheniformiswas measured and expressed as the time to first decimal reduction (δ value) at a given recovery temperature and pH. Spores ofB. weihenstephanensiswere produced at 30°C and 12°C, and spores ofB. licheniformiswere produced at 45°C and 20°C.B. weihenstephanensisspores were then heat treated at 85°C, 90°C, and 95°C, andB. licheniformisspores were heat treated at 95°C, 100°C, and 105°C. Heat-treated spores were grown on nutrient agar at a range of temperatures (4°C to 40°C forB. weihenstephanensisand 15°C to 60°C forB. licheniformis) or a range of pHs (between pH 4.5 and pH 9.5 for both strains). The recovery temperature had a slight effect on the apparent heat resistance, except very near recovery boundaries. In contrast, a decrease in the recovery pH had a progressive impact on apparent heat resistance. A model describing the heat resistance and the ability to recover according to the sporulation temperature, temperature of treatment, and recovery temperature and pH was proposed. This model derived from secondary mathematical models for growth prediction. Previously published cardinal temperature and pH values were used as input parameters. The fitting of the model with apparent heat resistance data obtained for a wide range of spore treatment and recovery conditions was highly satisfactory.