Modelling, optimization and control of yeast fermentation processes in food industry

A macroscopic model describing the main physiological phenomena observed during the fed-batch baker’s yeast production process and including the influence of nitrogen on the key bio-mechanisms is proposed. First, on the basis of a set of biological reactions, inspired by the model of Sonnleitner and Käppeli, a model in which the nitrogen and glucose consumption are coordinated is proposed. Second, an attempt of estimating storage carbohydrate contents in yeast cells through an extension of this model is presented. The model is identified and validated with experimental data of fed-batch yeast cultures and successfully predicts the dynamics of cell growth, substrate consumption (nitrogen and carbon sources) and metabolite production (ethanol and storage carbohydrates). The developed model was used for the determination of optimal operating conditions, in the sense of a production criterion. To this end, two different approaches were used: a control vector parameterization approach and a semi-analytical formulation of the optimal operating policy. The two approaches were compared with numerical and experimental data. The results of the two approaches lead to the determination of similar optimal operation conditions, which have been implemented for a new experimental phase. Moreover, these optimal conditions are in agreement with the profiles obtained by industrial manufacturers through an empirical optimization of the process.Doctorat en Sciences de l'ingénieur