Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2004
Publication Date: 4/1/2005
Citation: Novak, J.S., Call, J.E., Tomasula, P.M., Luchansky, J.B., 2005. An assessment of pasteurization treatment of water, media, and milk with respect to bacillus spores. Journal of Food Protection. Vol.68. No.4 pg. 751-757.
Interpretive Summary: Current milk pasteurization conditions may be inadequate for the assurance of safety from spore-forming bacteria. Bacillus cereus is the most likely pathogenic soil bacterium to be found in milk being transmitted from contaminated silage through the bovine gastrointestinal tract to fecal matter that externally contaminates the udder and gets passed on to raw milk. Bacillus anthracis although rarely associated with milk has become an agent of concern with respect to recent world events. Both microorganisms produce highly heat resistant dormant spores capable of surviving standard pasteurization conditions. This study examined the effectiveness of prescribed time and temperature conditions used in the pasteurization of milk products against spores of B. cereus and B. anthracis. Results showed that pasteurization alone without added interventions could not prevent survival of the spores in milk products. Additional measures combined with pasteurization may be necessary to ensure the wholesomeness and safety of dairy products.
Technical Abstract: This study evaluated the ability of spore-forming Bacillus spp. to resist milk pasteurization conditions from 72 to 150C. Spores from the avirulent surrogate Sterne strain of B. anthracis as well as a representative strain of a common milk contaminant that is also a pathogen, B. cereus ATCC, were heated at test temperatures for up to 90 min in dH2O, brain heart infusion medium (BHI), or skim milk. In skim milk, characteristic log reductions in CFU/ml for B. anthracis spores were 0.45 after 90 min at 72C, 0.39 after 90 min at 78C, 8.10 after 60 min at 100C, 7.74 after 2 min at 130C, and 7.43 after 0.5 min at 150C. Likewise, log reductions in CFU/ml for viable spores of B. cereus ATCC 9818 in skim milk were 0.39 after 90 min at 72C, 0.21 after 60 min at 78C, 7.62 after 60 min at 100C, 7.37 after 2 min at 130C, and 7.53 after 0.5 min at 150C. No significant differences (P < 0.05) in thermal resistance were observed for comparisons of spores heated in dH2O or BHI compared to results observed in skim milk for either strain tested. However, spores from both strains were highly resistant (P < 0.05) to changes in temperature. As such, pasteurization alone would not ensure complete inactivation of these spore-forming pathogens in dH2O, synthetic media, or skim milk.