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 environmen tal variables, such as temperature or pH. It has been demonstrated that suc h data can be used to predict bacterial growth in food products, both under conditions of constant and fluctuating temperatures. The purpose of the pr esent 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 we re attained for Escherichia coli W3110 immobilised in agar at fixed tempera tures. Growth data were then fitted using predictive microbial models to re present growth in lag, exponential and stationary phases. When compared to growth in liquid cultures, similar values were found for maximum exponentia l growth rate. Next, experiments were conducted whereby a 91 vessel was fil led 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 vesse l, and bacterial growth was consequently modelled as a function of temperat ure inside the vessel. Experimental results for bacterial growth showed goo d agreement with theory. The results show that it is feasible to combine en gineering and microbial models. (C) 2000 Elsevier Science Ltd. All rights r eserved.