Response surface optimization of enzymatic hydrolysis of Cistus ladanifer and Cytisus striatus for bioethanol production

Current ethanol production processes using crops such as sugar cane and corn are well established; however, utilization of a cheaper substrate such as lignocellulose could make bioethanol more competitive with fossil fuel, without the ethical concerns associated with the use of potential food resources. The sequential configuration employed to obtain cellulosic ethanol implies that the solid fraction of pretreated lignocellulosic material undergoes hydrolysis. In this work, the enzymatic hydrolysis of pretreated Cistus ladanifer and Cytisus striatus was studied following an experimental design as a statistical problem solving approach. Plackett–Burman design was used in order to select the most important variables from the simultaneous study on influence of operating and reactional conditions, and central composite design to optimize the process of enzymatic hydrolysis.The optimization of enzymatic hydrolysis using the response surface methodology allowed a study on the influence of the variables (pH, temperature, cellulases concentration, polymer (PEG) concentration and incubation time) and variability due to the type of substrate (C. ladanifer and C. striatus) used. From the obtained results it can be concluded that the enzymatic hydrolysis was clearly enhanced by temperature, cellulase concentration, and incubation time. Model validation showed a good agreement between experimental results and the predicted responses.