Effect of the internal water activity of bacterial spores on their heat resistance in water

The water contents and effective a_w of the core, cortex, and coat of spores in water, as well as the masses of the core, cortex, and coat plus exosporium in the dry state, are calculated from volumes, dry densities, and water absorption isotherms of the sporal components. From data presented here for spores ofBacillus subtilis var.niger andBacillus cereus T, and from previously published data forBacillus stearothermophilus, the logarithm of the heat resistance of the spores in water is linearly related to the effective a_w of their core and cortex.