Mycobacterium Paratuberculosis and the Commercial Pasteurization of Milk

Abstract

This paper considers the heat resistance of Mycobacterium paratuberculosis in milk from an engineering perspective. The aim is to assess some of the experimental heating techniques used in the determination of heat resistance and to identify whether the microbiological results obtained can be influenced by the technique used. The major experimental techniques are analysed on the basis of theoretical heat transfer mechanisms, and the flow regimes in the holding tubes, as well as being compared with commercial continuous pasteurization practice. The paper concludes that the thermal process delivered during milk pasteurization is relatively unaffected by particle diameter. Thus, in practical terms, clumping of cells of Mycobacterium paratuberculosis, previously suggested as a mechanism by which the organism survives pasteurization, is unlikely to reduce the effectiveness of the normal pasteurization process. The experimental methods used to determine heat resistance must be adequately characterized and understood, such that the thermal process delivered can be consistently quantified. Failure to achieve this may lead to inappropriate conclusions being drawn and the possibility of inherent errors and variability in the experimental data. The incorporation of engineering skills into such microbiological studies, would provide a much improved understanding of the true conditions imposed on the target micro-organisms. It would highlight how the experimental conditions relate to industrial practice and enable the impact of errors on the kinetic data to be quantified. In addition it may offer the opportunity in the future for the development of improved experimental and analytical techniques for such work.