Heat resistance of Bacillus spp. spores isolated from cow's milk and farm environment

The aim of this study was to compare heat resistance of the spores of mesophile Bacillus spp. from raw milk (bulk tank milk and milk from individual cows) and farm environment (faeces, silage, litter, swabs from skin and udder) as related to their survival in heat- treated dairy products. Fifty-eight strains of 9 species of Bacillus were tested for termoresistance within the temperature range of 95 - 135 degreesC and various exposure times. The highest termoresistance was found in B. licheniformis spores, which survived the temperature of 135 degreesC. Except for the spores B. coagulans and B. pumilus all remaining spores were able to germinate after heat treatment of up to 120 degreesC. The greatest reduction of the spore numbers was found in B. cercus. The results indicate that some Bacillus spores may survive in milk even after heat treatment.