Modelling of the alcohol dehydrogenase production in baker's yeast

A mathematical model was formulated to simulate cell growth and enzyme production during the aerobic and micro-aerobic culture of the yeast Saccharomyces cerevisiae. Model development was based on three simplified metabolic events in the yeast: glucose fermentation, glucose oxidation and ethanol oxidation. Cell growth was expressed as a composite of these metabolic events. Their contributions to the total specific growth rate depended on the activities of the pacemaker enzyme pools of the individual pathways. The effect of substrate concentrations on the specific growth rate was described by a Michaelis–Menten equation. It was assumed that enzyme formation is cell growth associated. The model successfully predicted the dynamics of cell growth, glucose consumption, ethanol metabolism and alcohol dehydrogenase (ADH) production. A good agreement between model simulations and experimental data was achieved. It was observed that ADH production depends on the available oxygen concentration in the medium. In general, the proposed model appears to be useful for the design, scale-up, control and optimization of alcohol dehydrogenase production.