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Flow Characteristics of a Pilot-Scale High Temperature, Short Time Pasteurizer^*

Dairy Processing and Products Research Unit, US Department of Agriculture, Eastern Regional Research Center, Agricultural Research Service, Wyndmoor, PA 19038

Corresponding author: P. M. Tomasula; e-mail: ptomasula{at}errc.ars.usda.gov.

In this study, we present a method for determining the fastest moving particle (FMP) and residence time distribution (RTD) in a pilot-scale high temperature, short time (HTST) pasteurizer to ensure that laboratory or pilot-scale HTST apparatus meets the Pasteurized Milk Ordinance standards for pasteurization of milk and can be used for obtaining thermal inactivation data. The overall dimensions of the plate in the pasteurizer were 75 x 115 mm, with a thickness of 0.5 mm and effective diameter of 3.0 mm. The pasteurizer was equipped with nominal 21.5- and 52.2-s hold tubes, and flow capacity was variable from 0 to 20 L/h.

Tracer studies were used to determine FMP times and RTD data to establish flow characteristics. Using brine milk as tracer, the FMP time for the short holding section was 18.6 s and for the long holding section was 36 s at 72°C, compared with the nominal times of 21.5 and 52.2 s, respectively. The RTD study indicates that the short hold section was 45% back mixed and 55% plug flow for whole milk at 72°C. The long hold section was 91% plug and 9% back mixed for whole milk at 72°C. This study demonstrates that continuous laboratory and pilot-scale pasteurizers may be used to study inactivation of microorganisms only if the flow conditions in the holding tube are established for comparison with commercial HTST systems.

Key Words: pasteurization • milk • Foot-and-Mouth Disease • Mycobacterium paratuberculosis

Abbreviation key: FMD = Foot-and-Mouth Disease, FMP = fastest moving particle, Mptb = Mycobacterium paratuberculosis, RTD = residence time distribution

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