Sporulating behavior influences the population dynamics of sporeformers during raw milk holding.

Document Type


Publication Date



American Dairy Science Association


Journal of Dairy Science




Suppl. 2






sporulation, spore, Bacillus


Thermoduric sporeformers are predominant in raw milk and form thermoduric endospores. Our previous research showed these sporeformers to cause biofouling of dairy contact surfaces and membranes, leading to cross contamination of final products. A critical factor influencing thermal inactivation is their form as vegetative cells or endospores. It would thus be of interest to understand the population dynamics of sporeformers in raw milk during storage at low temperatures. In our previous study, a low sporulating strain of Bacillus licheniformis showed an increasing trend in vegetative cell population during 72 h of storage at 10°C or higher, while maintaining spore population relatively static. In continuation, this study investigates population dynamics of a high sporulating strain of B. licheniformis (ATCC 14580). Raw milk samples were separately spiked with an average 4.0 log vegetative cells and 2.0 log spores/mL, and stored at 4°, 6°, 8°, 10°, and 12°C for 0, 24, 48, and 72 h. Standard protocols were followed for enumerating vegetative cells and spores. Three trials were conducted, in replicates of 3, and means were compared using ANOVA. Contour plots were developed using quadratic regression models to predict the population of vegetative cells and spores. In the vegetative cell spiking study, cell population remained mainly unchanged for 72 h up to 10°C, with more than 1.0 log change observed only at 12°C. As it was a sporulating strain, the spore spiking study validated a shift toward spores during storage at 4° to 8°C, with evidence of some parallel germination at 10°C or higher. The regression models helped us to develop contour plots across the holding temperature and duration. Based on the initial cell population of the spore former, such contour plots would help predict the presence of vegetative cells and spore populations in raw milk at a given time and temperature. This information will prove useful in optimizing raw milk holding conditions to keep the sporeformer population toward vegetative cells, which can subsequently be inactivated easily with thermal treatments such as pasteurization.