Prediction of the adherence, growth and release of microorganisms in production chains

The aim of this study was to develop a mathematical model that describes the bacterial contamination of food as a result of adherence, growth and release of bacteria in process equipment. The model developed can be applied to control the bacterial quality of food products produced in process chains in which the final contamination of the product is governed by growth and heat-induced destruction of bacteria. To set up the model, experiments were carried out with a plate heat exchanger using milk inoculated with Streptococcus thermophilus. The growth rate of S. thermophilus in milk could be described accurately by the modified expanded model of Ratkowsky. The observed increase in the concentration of S. thermophilus in milk at the outlet of the plate heat exchanger could be described quantitatively by the model. To predict the contamination of the product, the model was integrated into NIZO-PCS (Process Chain Simulator). The results of computer simulations were validated by a number of measurements in a cheese factory. It turned out that the agreement between the measured and calculated concentrations of S. thermophilus was sufficient for the model to be used for predictions in industrial production chains. (C) 2002 Elsevier Science B.V. All rights reserved.