Modelling the influence of metabolite diffusion on non-starter lactic acid bacteria growth in ripening Cheddar cheese

The influence of metabolite diffusion within the cheese matrix on growth of non-starter lactic acid bacteria (NSLAB) during Cheddar cheese ripening was mathematically modelled. The model was calibrated at a realistic range of diffusion of metabolites and the decay and growth parameters of immobilised starter LAB (SLAB) and NSLAB colonies, respectively. Metabolite diffusion is the limiting factor for NSLAB growth only if essential metabolite molecules are extremely large or otherwise immobilised in the matrix. For relatively small molecules diffusion cannot be a limiting factor; the diffusive replenishment of small molecule nutrients around the NSLAB colonies consuming them is generally faster than the release rate from all possible sources within the curd. Assuming that the only nutrient source limiting NSLAB growth is the release of metabolites from lysed SLAB colonies, the decay rate of SLAB, rather than metabolite diffusion, most probably determines the rate of NSLAB growth during Cheddar cheese ripening.