Liquefaction of hydrothermally pretreated wheat straw at high-solids content by purified Trichoderma enzymes

Enzymatic liquefaction was studied by measuring continuously the flowability change of high-solids lignocellulose substrates using a real time viscometric method. Hydrolysis experiments of hydrothermally pretreated wheat straw were carried out with purified enzymes from Trichoderma reesei; Cel7A, Cel6A, Cel7B, Cel5A, Cel12A and Xyn11A. Results obtained at 15% (w/w) solids revealed that endoglucanases, in particular Cel5A, are the key enzymes to rapidly reduce the viscosity of lignocellulose substrate. Cellobiohydrolases had only minor and the xylanase practically no effect on the viscosity. Efficient, fast liquefaction was obtained already at a dosage of 1.5 mg of Cel5A/g dry solids. Partial replacement or supplementation of Cel5A by the other major hydrolytic enzymes did not improve the liquefaction. The reduction of viscosity did not correlate with the saccharification obtained in the same reaction, suggesting that efficient liquefaction is rather dependent on the site than the frequency of enzymatic cleavages.