5-13: Importance of xylanases and mannanases in the total hydrolysis of biomass

Biomass plays an increasingly important role for the production of renewable platform chemicals and energy carriers such as bioethanol. In order to obtain a feasible production of biofuels from biomass, an efficient total hydrolysis of biomass is required. The hydrolysis is, however, hampered by the recalcitrant structure of the raw material. To avoid limitations of hydrolysis by structural factors, various pretreatment methods are available to increase the accessibility of cellulose and to modify the lignin and hemicellulose content of the lignocelluloses. Lignin and hemicelluloses have been recognised to decrease the hydrolysability by forming a complex matrix around the cellulosic microfibrils.

 This study focused on revealing the structural impacts of the individual hemicellulose components on the hydrolysis of softwood substrates. The hydrolysis of different pretreated lignocellulosic materials with varying hemicellulose contents was studied using combinations of purified enzyme preparations, including Trichoderma reesei Cel7A, Cel6A, Cel5A, Cel7B, Xyn11, Man5A and Aspergillus niger Cel3A β-glucosidase. Complementation of a basic cellulase mixture with hemicellulases clearly enhanced the overall degree of hydrolysis, as well as the hydrolysis of cellulose. The hydrolysis of cellulose in substrates, rich in glucomannans, was clearly improved by addition of mannanases, and the simultaneous removal of mannans and xylans improved the overall conversion of lignocelluloses to sugars.