Anne Richelle

Macroscopic modelling of baker's yeast production in fed-batch cultures and its link with trehalose production

Abstract A macroscopic model describing the influence of nitrogen on a fed-batch bakers yeast production process is proposed. First, on the basis of a set of biological reactions, inspired by the model of Sonnleitner and Kappeli (1986) , a model in which the nitrogen and glucose consumption are coordinated is proposed. Second, an attempt of estimating trehalose concentration in yeast cells through an extension of this model is presented. The model parameters are obtained via a non-linear least squares identification. It is validated with experimental data and successfully predicts the dynamics of growth, substrate consumption (nitrogen and carbon sources) and metabolite production (ethanol and trehalose). This model allows, on the one hand, quantitatively describing the link between nitrogen and glucose consumption in yeast cultures and, on the other hand, will be valuable for the determination of culture conditions aiming at maximizing yeast productivity while guaranteeing the accumulation of a required amount of trehalose.

Macroscopic modelling of bioethanol production from potato peel wastes in batch cultures supplemented with inorganic nitrogen

Inorganic nitrogen supplementation is commonly used to boost fermentation metabolism in yeast cultures. However, an excessive addition can induce an opposite effect. Hence, it is important to ensure that the ammonia supplemented to the culture leads to an improvement of the ethanol production while avoiding undesirable inhibition effects. To this end, a macroscopic model describing the influence of ammonia addition on Saccharomyces cerevisiae metabolism during bioethanol production from potato peel wastes has been developed. The model parameters are obtained by a simplified identification methodology in five steps. It is validated with experimental data and successfully predicts the dynamics of growth, substrate consumption (ammonia and fermentable sugar sources) and bioethanol production, even in cross validation. The model is used to determine the optimal quantity of supplemented ammonia required for maximizing bioethanol production from potato peel wastes in batch cultures.