A combined model to predict the functionality of the bacteriocin-producing Lactobacillus sakei strain CTC 494

The use of bacteriocin-producing lactic acid bacteria for improved food fermentation processes seems promising. However, lack of fundamental knowledge about the functionality of bacteriocin-producing strains under food fermentation conditions hampers their industrial use. Predictive microbiology or a mathematical estimation of microbial behavior in food ecosystems may help to overcome this problem. In this study, a combined model was developed that was able to estimate, from a given initial situation of temperature, pH, and nutrient availability, the growth and self-inhibition dynamics of a bacteriocin-producing Lactobacillus sakei CTC 494 culture in (modified) MRS broth. Moreover, the drop in pH induced by lactic acid production and the bacteriocin activity toward Listeria as an indicator organism were modeled. Self-inhibition was due to the depletion of nutrients as well as to the production of lactic acid. Lactic acid production resulted in a pH drop, an accumulation of toxic undissociated lactic acid molecules, and a shift in the dissociation degree of the growth-inhibiting buffer components. The model was validated experimentally.