The growth of Escherichia coli in a food simulant during conduction cooling:: combining engineering and microbiological modelling

Several studies have been conducted over the last decade to accumulate data on the growth of food-borne bacteria as a function of different environmental variables, such as temperature or pH. It has been demonstrated that such data can be used to predict bacterial growth in food products, both under conditions of constant and fluctuating temperatures. The purpose of the present study was to combine bacterial growth modelling with a heat transfer model describing the spatial temperature changes within a solid object, and to validate the model experimentally. Firstly, experimental growth data were attained for Escherichia coli W3110 immobilised in agar at fixed temperatures. Growth data were then fitted using predictive microbial models to represent growth in lag, exponential and stationary phases. When compared to growth in liquid cultures, similar values were found for maximum exponential growth rate. Next, experiments were conducted whereby a 91 vessel was filled with agar inoculated with E. coli and conduction cooled in a water bath. A finite difference scheme was used to model heat transfer from the vessel, and bacterial growth was consequently modelled as a function of temperature inside the vessel. Experimental results for bacterial growth showed good agreement with theory. The results show that it is feasible to combine engineering and microbial models. (C) 2000 Elsevier Science Ltd. All rights reserved.