ISSN 1330-9862 review (FTB-2353) Unstructured Models for Lactic Acid Fermentation – A Review Abdallah Bouguettoucha 1 , Béatrice Balannec 2,3 and Abdeltif Amrane 2,3 * 1 Laboratory of Chemical Engineering Process, Faculty of Technology, Ferhat Abbas University, DZ-19000 Setif, Algeria 2 National School of Chemistry of Rennes, University of Rennes 1, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, FR-35708 Rennes Cedex 7, France 3 European University of Brittany, 5 Boulevard Laënnec, FR-35000 Rennes, France Received: September 28, 2009 Accepted: December 22, 2009 Summary To describe a microbial process, two kinds of models can be developed, structured and unstructured models. Contrary to structured models, which take into account some basic aspects of cell structure, their function and composition, no physiological characteri- zation of cells is considered in unstructured models, which only consider total cellular concentration. However, in spite of their simplicity, unstructured models have proven to accurately describe lactic acid fermentation in a wide range of experimental conditions and media. A partial link between cell growth and production, namely the Luedeking and Piret model, is mostly considered by the authors. Culture pH is the main parameter to be considered for model development. Acidic pH leads to inhibitory concentrations of undis- sociated lactic acid, the main inhibitory component, which causes cessation of growth and then production. On the other hand, pH control at optimal value for LAB growth allows to overcome product inhibition (by the total lactic acid produced or its undissociated part); hence nutritional limitations have to be considered for model development. Nitrogen is mainly involved in cessation of growth, owing to the fastidious nutritional requirements of LAB, while lactic acid production ceased when carbon was exhausted from the me- dium. The lack of substrate inhibition when usual concentrations of carbon substrate are used should be noted. Key words: lactic acid bacteria, growth inhibition, unstructured models, nutritional limita- tions Introduction Kinetic models enable bioengineers to design and con- trol microbial processes. Mathematical models, together with carefully designed experiments, allow the improve- ment of the evaluation and knowledge concerning sys- tem behaviour (1). To describe a microbial process, two kinds of models can be developed, structured and un- structured models. Structured models take into account some basic aspects of cell structure, their function and composition, and have been reported to accurately de- scribe lactic acid fermentation (1,2), but they can seem complex. Only total cellular concentration is considered in unstructured models, and hence they do not involve any physiological characterization of the cells. However, they have proven to accurately describe lactic acid fer- mentation in a wide range of experimental conditions and media (3–8). An exhaustive review of the available 3 A. BOUGUETTOUCHA et al.: Models for Lactic Acid Fermentation, Food Technol. Biotechnol. 49 (1) 3–12 (2011) *Corresponding author; Phone: ++33 2 2323 8155; Fax: ++33 2 2323 8120; E-mail: abdeltif.amrane@univ-rennes1.fr