Heat Resistance Assay and Identification for Bacillus spp. spores Isolated from Raw Milk

Heat-resistant spore-forming Bacillus spp. can survive the heat treatment process of milk and lead to spoilage of the final product. The objective of the research is to assay heat-resistant ability (D values, minutes) for Bacillus spp. spores. A total of 7 Bacillus spp. spores from eight of raw milk samples were tested biochemical properties and measured heat resistance in 1% peptone solutions. The best heat-resistant spores were chosen to identify them by 16S rRNA genes sequencing. The results showed that all of them belonged to the species of genus Bacillus, survived at the heat treatment of 90 °C for 12 minutes with the D values ranging from 1.86 to 23.66 minutes. Among of them, the best heat-resistant spores, namely BT2 and OM1, survived at the heat treatment of 100 °C for 30 minutes with the D values of 8.78 and 4.89 minutes, respectively; and were identified as Bacillus sporothermodurans BT2 and Bacillus cereus OM1, respectively.