The influence of transport phenomena during high-pressure processing of packed food on the uniformity of enzyme inactivation

Here we deal with the influence of heat-transport effects on a high-pressure-induced enzyme inactivation in packed substances. Special attention is given to the influence of the geometrical scale and to the heat-transfer characteristics of the packaging material. The investigation is based on mathematical modeling and numerical simulation. The method accounts both for compression phase and holding phase. The model includes convective and conductive heat transfer, fluid motion as well as an enzyme transport equation with a first-order kinetic source term accounting for the inactivation. Three configurations with a total volume of 0.8 L, 6.3 L, and 50.3 L are considered. The pressure medium is water. The enzyme solution is B. subtilis a-amylase dissolved in a TRIS-HCl-buffer. The packaging material is polypropylene. The heat-transfer coefficient for conduction through the packaging material is varied to simulate both changes in the material properties as well as modifications of the packaging material thickness. It is found that the efficiency of the inactivation increases with increasing chamber volume as long as the kinetic inactivation constant is increasing with temperature. In the considered case the activity retention obtained in a 0.8 L volume is about 2.4 times larger than the one obtained for the same process carried out in a 50.3 L volume. Furthermore, it was found that the properties of the packaging material could induce a significant degree of nonuniformity (worst case = 69%). An appropriate choice of the material can lead to maximum inactivation and maximum process uniformity since advantage is taken from the slow heat exchange after the compression phase. (C) 2003 Wiley Periodicals, Inc.