Germination of Bacillus cereus ATCC 14579 spore at various conditions and inactivation of the germinated cells with microwave heating and UVC treatment in milk samples

Abstract

In this study, germination of Bacillus cereus spores under various conditions and the inactivation of germinated cells by microwave heating (MH) and 254 nm ultraviolet (UVC) treatment in milk samples were identified. A combination of germinants, ʟ-alanine and inosine, was the most effective for germination of B. cereus spores; and heat activation during the germination step increased the germination rate to 99.98% at pH 7 with 1% sodium chloride. The resistances of germinated cells by optimized conditions, inoculated in milk samples, to MH and UVC were investigated. The reduction rate was the highest in skimmed milk followed by low-fat and whole milk samples. The resistance of germinated cells was significantly higher than that of the vegetative cells regardless of the milk type. Sequential treatments exhibited a higher reduction rate than the sum of individual treatments, and resuscitation of germinated cells was not observed even after the longest treatment. Moreover, the quality aspects of milk samples were not significantly deteriorated (p > 0.05) except for the pH values which were found to be slightly decreased. These results would be used as a fundamental database for the application of UVC and MH to inactivate B. cereus spores in milk samples.