Visualization and modelling of the thermal inactivation of bacteria in a model food

A large number of incidents of food poisoning have been linked to undercook ed meat products. The use of mathematical modelling to describe heat transf er within foods, combined with data describing bacterial thermal inactivati on, may prove useful in developing safer food products while minimizing the rmal overprocessing. To examine this approach, cylindrical agar blocks cont aining immobilized bacteria (Salmonella typhimurium and Brochothrix thermos phacta) were used as a model system in this study. The agar cylinders were subjected to external conduction heating by immersion in a water bath. They were then incubated, sliced open, and examined by image analysis technique s for regions of no bacterial growth. A finite-difference scheme was used t o model thermal conduction and the consequent bacterial inactivation. Bacte rial inactivation rates were modelled with values for the time required to reduce bacterial number by 90% (D) and the temperature increase required to reduce D by 90% taken from the literature. Model simulation results agreed well with experimental results for both bacteria, demonstrating the utilit y of the technique.