When the milk flow in a holding tube is turbulent, the fastest flowing particle travels 1.1 times faster than the average particle. The Re indicates whether flow in a pipe is laminar (Re 3,000) ( 15). This parameter can be derived from the flow velocity, tube diameter, fluid viscosity, and fluid density. The Reynolds number (Re) describes the type of flow. paratuberculosis have discussed turbulent flow as an important feature of commercial pasteurization (see references 7, 12, and 26). Some of the groups studying the heat inactivation of M. The likely raw milk contamination level is not known with any certainty, with estimates ranging from 6 log 10 ( 26). Some asymptomatic animals can also shed M. Up to 8 CFU/50 ml have been reported, but only a proportion of the milk from clinically affected cows yielded positive cultures ( 27, 29, 30). Aseptically removed milk from clinically affected cows may have low levels of M. Direct excretion in the milk is likely to be less significant than fecal contamination. Levels as high as 10 8 CFU/g have been reported ( 3). paratuberculosis at varying levels in their feces. Animals with clinical Johne's disease excrete M. A major source is from fecal contamination of the udder. Under normal milking conditions, bulk raw milk from an infected herd will probably be contaminated with M. It has been suggested that this bacterium may also play a role in the etiology of Crohn's disease in humans (for a review, see reference 1). paratuberculosis is the cause of Johne's disease, a chronic bowel disease of dairy cows and other ruminants that has a worldwide distribution. An additional safeguard is the widespread commercial practice of pasteurizing 1.5 to 2° above 72☌. paratuberculosis in retail milk and other pasteurized dairy products. Properly maintained and operated equipment should ensure the absence of viable M. After heating at 72☌ for 15 s, the minimum M. Milk was inoculated with fresh fecal material from a high-level fecal shedder with clinical Johne's disease. These five strains showed similar survival whether recovery was on Herrold's egg yolk medium containing mycobactin or by a radiometric culture method (BACTEC). The mean Z value (degrees required for the decimal reduction time to traverse one log cycle) was 8.6☌. The mean extrapolated D 72☌ was 7 log 10 kill at 72☌ for 15 s (95% confidence interval). Means of pooled D values (decimal reduction times) at 63 and 66☌ were 15.0 ± 2.8 s (95% confidence interval) and 5.9 ± 0.7 s (95% confidence interval), respectively. No strains survived at 72☌ for 15 s and only one strain survived at 69☌. The ATCC 19698 type strain, ATCC 43015 (Linda, human isolate), and three bovine isolates were heated in raw whole milk for 15 s at 63, 66, 69, and 72☌ in duplicate trials. A pilot-scale pasteurizer operating under validated turbulent flow (Reynolds number, 11,050) was used to study the heat sensitivity of Mycobacterium avium subsp.
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