Author:

Keywords:

Listeria innocua, Lactococcus lactis, Predictive microbiology, Modelling, Gelatin, Buffering capacity, Lactic acid dissociation, Science & Technology, Life Sciences & Biomedicine, Food Science & Technology, Microbiology, predictive microbiology, modelling, gelatin, buffering capacity, lactic acid dissociation, SALMONELLA-TYPHIMURIUM, ESCHERICHIA-COLI, RUBBERY STATES, SURVIVAL, GLASSY, GEL, Coculture Techniques, Colony Count, Microbial, Food Microbiology, Hydrogen-Ion Concentration, Kinetics, Lactic Acid, Listeria, Mathematics, Models, Biological, Predictive Value of Tests, 0605 Microbiology, 0908 Food Sciences, 1003 Industrial Biotechnology, 3006 Food sciences, 3107 Microbiology

Abstract:

A new class of predictive model developed in a liquid system is extended in order to quantify gelatin gel matrix structure effects on the growth of Listeria innocua and Lactococcus lactis (both in mono- and coculture, and both producing mainly lactic acid). It was observed that gelatin does not only act as a structuring agent but also alters the buffering capacity of the medium. Model extension occurs in two stages, describing chemical and microbiological processes, respectively. Firstly, equations relating undissociated lactic acid concentration and total lactic acid concentration on the one hand, and undissociated lactic acid concentration and pH on the other hand, are extended to account for the effects of gelatin concentration. Secondly, these equations are incorporated into the growth model to describe the combined effect of gelatin concentration, (undissociated) lactic acid and pH on the growth of either microorganism. The description of the model is in good agreement with the experimental data acquired in monoculture conditions. In a subsequent model validation step, when gelatin concentration and total lactic acid profile of the coculture experiments are used as inputs, the developed growth model consisting of condensed knowledge extracted from the monoculture experiments, is able to predict accurately the interaction effect occurring in coculture. The study suggests that, on the one hand, the extent of the effects of undissociated lactic acid and pH on microbial growth in structured food systems can be modified by the increase in buffering capacity, which can protect microorganisms and eventually promote higher levels of cell growth in comparison with liquid culture conditions. On the other hand, food matrix structure, in casu the gelatin, reduces the rate of microbial multiplication. Both effects are incorporated in the growth model developed in this research.