Purpose: To understand the problematic spores of bacilli commonly found in dairy powders collected from 11 dairy powder plants located across the US.
Methods: Raw ingredients (n=55) and dairy powders (n=33) were collected from 11 powder plants for over a period of 6 months. All samples were subjected to 3 spore tests; spore pasteurization (SP; 80°C for 12 min), highly heat resistant (HHR; 100°C for 30 min) and specially thermoresistant spore enumeration (STSE; 106°C for 30 min), followed by incubation for 24-48h at 32 °C and 55 °C for enumeration of mesophilic spore counts (MSC) and thermophilic spore counts (TSC), either obtained by direct plating or enrichment, respectively. All sporeformers were characterized and identified using rpoB gene (~632 bp) sequencing method.
Results: Overall dairy powders collected from 11 plants shows significantly higher counts of aerobic spores compared to raw ingredients. Out of the 329 sporeformers identified, Bacillus (n=263) was the predominant genus isolated, followed by B. licheniformis AT 1 (n=100) representing a ubiquitously distributed spore species and strain of all raw and powder samples.
Significance: The results provide an understanding of the sporeformers commonly found in powders processed in US dairy plants covering a wide geographical spread. Understanding the ecology of these sporeformers can provide insight into the prevalence and persistence of problematic spores, with the aid of developing strategies for monitoring and control.