Unstructured Models for Lactic Acid Fermentation – A Review

Abdallah Bouguettoucha¹, Béatrice Balannec^2,3 and Abdeltif Amrane<sup>2,3*

1</sup>Laboratory of Chemical Engineering Process, Faculty of Technology, Ferhat Abbas University, DZ-19000 Setif, Algeria
²National School of Chemistry of Rennes, University of Rennes 1, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, FR-35708 Rennes Cedex 7, France
³European University of Brittany, 5 Boulevard Laënnec, FR-35000 Rennes, France

Article history:
Received September 28, 2009
Accepted December 22, 2009

Key words:
lactic acid bacteria, growth inhibition, unstructured models, nutritional limitations

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 characterization 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 undissociated 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 medium. The lack of substrate inhibition when usual concentrations of carbon substrate are used should be noted.

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