17H-24 |
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E. PATAZCA1, H. S. Ramaswamy2, and J. Dunn1. (1) National Center for Food Safety & Technology, Illinois Institute of Technology, IIT Moffett Campus, 6502 S. Archer Rd., Summit-Argo, IL 60501-1923, (2) Dept. of Food Science & Agricultural Chemistry, McGill Univ., Macdonald Campus, 21111 Lakeshore Rd., Sainte-Anne-de-Bellevue, QC H9X 3V9, Canada There is considerable interest for high pressure processing (HPP) of low-acid shelf stable foods. HPP of low acid foods can either be a pressure(P) assisted thermal process or temperature(T) assisted pressure process. Either way, data on inactivation kinetics of pathogenic and surrogate microorganisms are needed under appropriate P/T conditions. During the hold time, the pressure generally remains constant while the temperature could drop by a few degrees due to heat loss from the product to equipment structure. The objective of this paper was to describe a methodology for making come-up and hold time corrections to first order kinetic models for microbial destruction under HPP. The methodology is based on approaches followed in traditional non-isothermal destruction kinetics. As in conventional kinetics, a first estimate of D-value (negative reciprocal slope of log-residual survivor vs time) at each process pressure condition is made based on uncorrected time, from which a nominal z(T)-value is obtained (negative reciprocal slope of log-D value vs time). These initial D and z(T) values are then used to get a more accurate thermal time based on the actual pressure-time data, from which more accurate D and subsequently z(T)-value are obtained. These steps are repeated several time for the convergence of D and z(T) value to the real values. This will result in a set of D and z(T) value for each pressure. In the next step similar corrections are made for the temperature. Finally, from the computed values, a set of D and z(P) values are obtained complete the picture. Corrections for kinetic data on inactivation of B. stearothermophilus under HPP showed that there is a significant difference between the conventional values and those obtained with the correction proving that corrections need to be done to better approach real HPP sterilization values. Ignoring the come-up time will diminish the transient P/T contributions to process lethality, while ignoring the temperature drop during the process could result in under processing therefore kinetic data established for HPP without reference to these transient conditions may lack precision.
Session 17H, Food Engineering: Thermal processes
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