Role of lignin in the enzymatic hydrolysis of lignocellulose

Characterization, understanding and overcoming barriers of enzymatic hydrolysis of different raw materials is essential for the development of economically competitive processes based on enzymatic treatments. This work focused on factors relevant for the improvement of enzymatic hydrolysis of lignocellulose raw materials derived from softwood. The major interest of the work was in lignin. Specific areas addressed were the role of lignin in the unproductive binding of cellulases, which restricts the hydrolysis of cellulose, and enzymatic modification of lignin in order to improve cellulose hydrolysis. In addition, suitability a new pretreatment method, wet oxidation, was evaluated for softwood. The binding of Trichoderma reesei CBH I and CBH II enzymes on bacterial microcrystalline cellulose (BMCC) was shown to be determined by a cooperative effect of the two domains, the cellulose binding domain (CBD) and the catalytic domain (CD). Binding of the intact CBH I on bacterial microcrystalline cellulose (BMCC) was fully reversible, while the binding of CBH II was only partly reversible. The cellulases CBH I and EG II were adsorbed on steam pretreated softwood (SPS) and lignin. The observation that the presence of CBD clearly enhanced the binding of the enzymes on SPS and especially on lignin, suggests that unspecific adsorption is dominated by the affinity of the CBD. The wet oxidation pretreatment studies gave information on the importance of substrate structure in the enzymatic hydrolysis. This pretreatment method was applied to softwood for the first time. In the wet oxidation pretreatment studies, the total recovery of carbohydrates was high and the recovery of cellulose even higher than what has been reported for steam pretreated softwood. Lignin fraction of the substrate remained mainly undissolved. No clear correlation between the hydrolysis yield and lignin content could be observed. It was