Heat Resistance of Bacillus subtilis Spores at Various Water Activities

S ummary : The heat resistance of spores of Bacillus subtilis was determined in water vapour and in aqueous solutions of NaCl, LiCl, glucose and glycerol at various water activities. In water vapour and in glycerol solutions, maximal resistance appeared at low, but not zero water activity. In NaCl and glucose solutions only small variations in heat resistance occurred with decreasing water activity although a small increase was observed at the highest concentrations tested. With increasing concentrations of LiCl, heat resistance at first decreased but increased at water activities below 0·5. The possible interaction of compounds controlling water activity and water activity per se on heat resistance is discussed.