Ethanol regulation in yeast fed-batch cultures by stabilizing extremum seeking

In this study, an original model-free stabilizing extremum seeking (STAB-ESC) strategy is applied to optimize yeast fed-batch culture productivity. To this end, the ethanol concentration is tracked at a low level, to approach the yeast growth optimal conditions. Overflow metabolism effects, resulting from the cell's limited respiratory capacity, are considered using a macroscopic model with discontinuous kinetics. The detrimental impact of input saturation on the proposed STAB-ESC stability is overcome using a state-dependent switching control strategy. The resulting methodology is illustrated with numerical results where the robustness of the controller to measurement noise is also highlighted.