Analysis and practical implementation of a model for combined growth and metabolite production of lactic acid...

Next to the traditional application of lactic acid bacteria (LAB) as starter cultures for food fermentations, the use of LAB as protective cultures against microbial pathogens and spoilage organisms in other food production processes gains more and more interest. The inhibitory effect of LAB is mainly accomplished through formation of antimicrobial metabolites. In this paper, the model of Nicolaï et al. [Food Microbiol. 10 (1993) 229.], describing cell growth and production of lactic acid, which is the major end-product of LAB metabolism, is investigated. In contrast to classical predictive models, the transition of the exponential growth phase to the stationary phase is obtained through the increasing concentrations of undissociated lactic acid [LaH] and decreasing pH in the environment. To describe the variation in time of [LaH] and pH, a novel, robust calculation method is introduced. The model of Nicolaï et al. in combination with the novel method of [LaH] and pH computation is then further applied to an experimental data set of Lactococcus lactis SL05 grown in a rich medium. An accurate description of the measured values of cell concentration, total lactic acid concentration and pH is obtained.