Modelling of diffusion-limited growth to predict Listeria distribution in structured model foods

A major objective in the improvement of food safety is to predict the evolution of microorganisms in foods under defined conditions. In this work, a model has been developed that considers diffusional limitations during microbial growth in solid or paste foods, and it was applied to predict Listeria innocua growth in a solid medium under oxygen restrictions. The kinetics of L. innocua growing in a liquid broth under different oxygen concentrations were determined and results were incorporated to the model. Experiments to validate the model were conducted measuring the distribution and evolution of L. innocua growing in a solid κ-carrageenan model food. Preferential growth on the surface was measured in the solid food, being changes inside the medium much more limited. A good concordance was obtained between the model simulations and the experimental results in the solid food. Some slight differences were nevertheless observed on the surface due to the effect of the different environment surrounding the cells.