Date of this Version
Estrada-Anzueto, M. 2014. Tracking Heat-Resistant Sporeforming Bacteria in the Milk Chain: A Farm to Table Approach. Master's Thesis, University of Nebraska.
Sporeforming bacteria (such as Bacillus and Paenibacillus spp.) can survive pasteurization conditions (Collins, 1981) and grow in pasteurized fluid milk during refrigerated storage (Huck et al., 2008; Ivy et al., 2012), causing fluid milk spoilage and limiting the further extension of fluid milk’s shelf life (Fromm and Boor, 2004; Durak et al., 2006). Moreover, Bacillus and related genera have been found in raw milk, pasteurized milk and environmental samples from dairy farms, indicating that these organisms are ubiquitous in nature and can enter the milk chain from different sources (Huck et al., 2007b; Huck et al., 2008; Ranieri and Boor, 2009). The objective of this project was to evaluate the presence of Bacillus and related genera in a medium-size fluid milk chain in Nebraska to identify the source of these bacteria in packaged fluid milk. To achieve this, raw milk, pasteurized milk and environmental samples representing the farm-to-table continuum were collected from a dairy farm and a medium-size processing plant in Nebraska, supplied exclusively by that farm during Spring 2012, Fall 2012 and Spring 2013. Environmental and raw milk samples were heat-treated at 80°C for 12 minutes to eliminate vegetative cells. Pasteurized milk and heat-treated samples were stored at < 7°C for 21 days to enrich for psychrotrophic sporeformers. Samples were enumerated for microbial load and the plates were used for bacterial isolation throughout storage. Isolates were characterized using rpoB and/or partial 16S rDNA sequencing. A vast diversity of sporeforming bacteria (i.e. 94 and 42 unique rpoB and 16S rDNA allelic types, respectively) and many entry points of these organisms (i.e. raw milk supply, farm and plant environment) were identified all over the milk chain. Consequently, the control of sporeformers in pasteurized fluid milk will be challenging and will require specific control strategies applied throughout the farm-to-table continuum.
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