Stochastic model for a biological complex system: analysis of the bacterial growth in food products

The Physics of Complex Systems has recently taken a more and more important role in the description of natural systems because of the interactions, both deterministic and noisy, between such systems and the environment. In particular the noise plays a relevant role in biological systems, whose dynamics is strongly influenced by environmental variables subject to random fluctuations. In this work a stochastic model is exploited to reproduce the growth of bacteria in food of animal origin. Specifically the dynamics of a bacterial species, Listeria monocytogenes, is analyzed in the presence of lactic acid bacteria (LAB) during the period of the fermentation of meat products. The model, based on a generalization of the Lotka-Volterra equations in the presence of noise sources, takes into account the random fluctuations of physical and chemical variables such as temperature, pH and activity water, which are treated as stochastic variables. The presence in the model of appropriate levels of noise allows to obtain theoretical results in a good agreement with experimental data.