Optimisation de la production de l'acide lactique par voie fermentaire- description du processus à l'aide de modèles structurés et non structurés

Abstract

During lactic acid fermentation in batch and continuous culture using Lactobacillus helveticus, seed culture is usually carried out without pH control, while culture is carried out at pH controlled at the optimal value to overcome inhibitory effects. In this study, novel mathematical models are set up to describe lactic acid production in batch and continuous fermentation. The Luedeking-Piret expression was therefore previously modified by introducing additional terms involving the undissociated form of the lactic acid, the main inhibitory species, in case of batch cultures without pH control. To describe growth, the Verlhust model which proved to describe satisfactory growth kinetics was considered. The model was found to match both experimental growth and production data. Another model was also developed involving the residual lactose concentration to account for carbon substrate limitation, responsible for cessation of production during batch cultures of Lactobacillus helveticus at controlled pH. This model matched experimental data accurately. Two generalized models were then deduced from the above expressions. The results obtained show that the generalized models gave a satisfactory description of experimental data in various culture conditions, since they were validated during cultures at pH control and in absence of pH control, as well as for different nitrogen supplementation of culture media. Both models, as well as the Luedeking-Piret model, were developed to describe successfully continuous two-stage culture of L. helveticus