Model based control of minimal overflow metabolite in technical scale fed-batch yeast fermentation

The specific growth rate should ideally be maintained at maximum oxidative growth rate in order to maximize biomass yield and productivity in fed-batch yeast fermentations. However, a more conservative approach is adopted in industry where specific growth rate is kept below the critical value to prevent the accumulation of overflow metabolite ethanol by using predetermined feeding profiles. In this work, biomass growth is maintained just above maximum oxidative growth rate by regulating ethanol concentration in the fermenter. The state feedback linearizing control strategy is developed and applied to the technical scale fed-batch yeast fermentations. The proposed control algorithm is constructed on the reliable state estimation algorithm developed previously and the biomass concentrations and ethanol measurements are then used in the control algorithm. The ethanol concentration is successfully controlled at fixed and time varying set values. By this approach the specific growth rate is controlled just over the critical value by regulating minimal ethanol concentration in order to maximize the biomass productivity.