The role of glass transition temperature (T) and storage temperature (T) in explaining the survival behavior of dried Bacillus cereus.

Recent studies have indicated a correlation between glass-transition and desiccation tolerance in bacteria contaminating dry food. To validate and extend the applicability of this relationship, we focused on Bacillus cereus with underexplored glass-transition mechanisms. This study aims to investigate the vitrification characteristics of B. cereus and assess the potential of glass-transition temperature (T) in indicating bacterial survival behavior in desiccated environments. We measured the mechanical T and metabolic changes of dried B. cereus, prepared by different drying methods (air-drying and freeze-drying) and stored at various water activity (a) levels (0.43, 0.62, 0.75, and 0.87). The T of air-dried B. cereus cells was higher than that of freeze-dried cells, and unlike air-dried cells, freeze-dried cells did not show a decrease in T due to the increase in a. Changes in air-drying temperature and humidity had little effect on the T. Metabolite profiles varied with the drying method, indicating the potential for vitrification in B. cereus cells. In addition, we examined the survival of dried B. cereus cells under different storage temperatures (T; 4 °C, 25 °C, and 42 °C) and a levels (0.43 and 0.87). Freeze-dried cells were inactivated faster than air-dried cells across all T and a levels. Air-drying temperature and humidity had minimal impact on survival behavior. Furthermore, the difference between T and T (T - T) was considered an indicator of survival for dried bacteria. When the temperature differential (T - T) reached 18.27 °C, a clear distinction was observed between surviving and inactivated cells. Therefore, (T - T) can serve as an alternative parameter for predicting the desiccation tolerance of dried bacterial cells.