Influence of individual milk constituents on the heat resistance of Bacillus licheniformis and Bacillus stearothermophilus spores

Spores of Bacillus licheniformis had been found to be more, and those of Bacillus stearothermophilus less, heat resistant in skimmilk concentrate than in skimmilk. To find the reasons for the observed differences, the destruction of the specific spores was studied in media which had been deliberately altered. The spores of both species were stabilized as the water activity of the medium was decreased by the addition of different milk constituents (lactose, calcium, phosphate, casein). However, in the case of B. stearothermophilus the addition of calcium and phosphate increased the death rate although the water activity was lowered.