Modelling of diffusion-limited growth for food safety in simulated cheeses

Predicting microbial evolution in soft cheeses, which suffer the colonization of several pathogens, such as Listeria monocytogenes, is a main objective in the improvement of food safety conditions. In this work, a model that considers diffusional limitations during pathogen's growth in structured foods has been assayed. To test the feasibility of the model, Listeria innocua evolution with time and position was monitored in structured model cheeses prepared to mimic soft cheeses with different lactic acid contents. Prediction of biomass and substrate evolution requires to know the kinetics under different aeration conditions. L. innocua behaviour was also studied in broths prepared with similar composition to model cheeses, evaluating the effect of oxygen concentration on cell growth. The assayed model provided quite accurate results for low concentration of lactic acid, whereas for lactic acid concentrations higher than 3 g l−1 cell development in structured media was inhibited.