Optimal control strategies for simultaneous saccharification and fermentation of starch

Design and analysis of optimal control strategies for three types of inhibitory fed-batch bioprocesses have been discussed. These are simple saccharification (SS) of starch to glucose, simple fermentation (SF) of derived glucose to lactic acid (LA) and simultaneous saccharification and fermentation (SSF) of starch to LA. Various optimal feeding strategies have been investigated for the SSF process by manipulating starch addition rates. To avoid the complexity of solving a singular problem, the starch addition rates are expressed in terms of the broth volume, which is used as a control variable. The optimization strategy is thus solved in a nonsingular framework. Experimental studies carried out using the results of the optimization demonstrated the accuracy and utility of the approach. An increase of 20% in lactate productivity was obtained by operating the SSF process in a fed-batch mode. The focus of all the optimization studies has been to improve the performance of the SSF process. Optimal control of starch additions in the fed-batch process gave improved performance of the SSF process.