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Applied and Environmental Microbiology, April 2005, p. 1785-1789, Vol. 71, No. 4
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.4.1785-1789.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Heat Inactivation of Mycobacterium avium subsp. paratuberculosis in Milk

Wendy L. McDonald, Kimberly J. O'Riley, Christopher J. Schroen, and Robin J. Condron*

Department of Primary Industries, Victorian Institute of Animal Science, Attwood, Victoria, Australia

Received 7 October 2003/ Accepted 9 November 2004

The effectiveness of pasteurization and the concentration of Mycobacterium avium subsp. paratuberculosis in raw milk have been identified in quantitative risk analysis as the most critical factors influencing the potential presence of viable Mycobacterium paratuberculosis in dairy products. A quantitative assessment of the lethality of pasteurization was undertaken using an industrial pasteurizer designed for research purposes with a validated Reynolds number of 62,112 and flow rates of 3,000 liters/h. M. paratuberculosis was artificially added to raw whole milk, which was then homogenized, pasteurized, and cultured, using a sensitive technique capable of detecting one organism per 10 ml of milk. Twenty batches of milk containing 103 to 104 organisms/ml were processed with combinations of three temperatures of 72, 75, and 78°C and three time intervals of 15, 20, and 25 s. Thirty 50-ml milk samples from each processed batch were cultured, and the logarithmic reduction in M. paratuberculosis organisms was determined. In 17 of the 20 runs, no viable M. paratuberculosis organisms were detected, which represented >6-log10 reductions during pasteurization. These experiments were conducted with very heavily artificially contaminated milk to facilitate the measurement of the logarithmic reduction. In three of the 20 runs of milk, pasteurized at 72°C for 15 s, 75°C for 25 s, and 78°C for 15 s, a few viable organisms (0.002 to 0.004 CFU/ml) were detected. Pasteurization at all temperatures and holding times was found to be very effective in killing M. paratuberculosis, resulting in a reduction of >6 log10 in 85% of runs and >4 log10 in 14% of runs.

* Corresponding author. Present address: Dairy Australia, Locked Bag 104, Flinders Ln., Victoria 8009, Australia. Phone: 0011 61 3 9694 3831. Fax: 0011 61 3 96943833. E-mail: RCondron{at}dairyaustralia.com.au.

Applied and Environmental Microbiology, April 2005, p. 1785-1789, Vol. 71, No. 4
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.4.1785-1789.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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  • Bendall, J. G., Pearce, L. E. (2008). Letter to the Editor: Pasteurization Temperature of Milk: A Comment on Gandy et al. (2008). J DAIRY SCI 91: 4113-4114 [Full Text]  
  • Gandy, A. L., Schilling, M. W., Coggins, P. C., White, C. H., Yoon, Y., Kamadia, V. V. (2008). The Effect of Pasteurization Temperature on Consumer Acceptability, Sensory Characteristics, Volatile Compound Composition, and Shelf-Life of Fluid Milk. J DAIRY SCI 91: 1769-1777 [Abstract] [Full Text]  
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