Purpose: This study evaluated whether previously laboratory derived thermal inactivation data and conditions could be scaled-up and if real world processing parameters could inactivate B. anthracis spores.
Methods: Bacillus anthracis spores (6 log CFU/ml) were inoculated into large quantities of reconstituted skim milk and processed by a MicroThermics Bantam 1S at 105, 110 and 115°C. Temperature measurements were recorded and treated samples were collected at sample exit port. Milk sample was allowed to flow out of the exit port for 1 min prior to sample collection and approximately 1liter of sample was collected for microbiological analysis.
Results: The targeted processing temperatures at the end of the hold tube within the HTST will require the HTST to ramp up heating above the targeted temperature by approximately 7°C at the start of the hold tube. This heating profile resulted in anthrax spores being exposed to different temperatures and not uniformly distributed inactivation rates throughout the hold tube. At 105°C, a 15 s hold time was required to achieve a 6-log inactivation and temperatures within the hold tube ranged from 112°C at the start to 105°C at the end of the hold tube. At 110 and 115°C, a hold time of 5 and 2 s, respectively, were required to achieve a 6-log inactivation of anthrax spores. In addition to the processing temperatures and hold times, the Re values of > 8,000 and turbulent flow type were other important parameters.
Significance: This study identified processing conditions that resulted in the inactivation of anthrax spores in milk during thermal processing using pilot-scale processing equipment.