The effect of soluble phenolic compounds from hydrothermally pretreated wheat straw on Trichoderma reesei cellulases and commercial enzyme cocktails

Hydrothermal methods are commonly applied in pretreatment of lignocellulose for conversion to biofuels and chemicals. This pretreatment partially disassembles and solubilizes hemicelluloses and lignin, releasing sugars and phenolic compounds, which are potential inhibitors for the subsequent enzymatic saccharification step. In this work, the inhibitory effect of soluble phenolics in hydrothermal pretreatment liquor on canonical Trichoderma reesei enzymes was investigated, using purified cellobiohydrolases, endoglucanases, a xylanase, and a lytic polysaccharide monooxygenase, as well as commercial enzyme cocktails Cellic Ctec2 and Celluclast. The pretreatment liquor was fractionated to enrich the phenolics, and thoroughly analyzed. The most sensitive to phenolics inhibition were cellobiohydrolases, the major enzymes in crystalline cellulose degradation and the primary component in cellulolytic mixtures. These were inhibited by the oligophenolics and phenol-carbohydrate complexes (lignin-carbohydrate complex type of compounds), the latter of which could be mitigated by other enzymes, i.e., xylanases and endoglucanases. Addition of lytic polysaccharide monooxygenase to the hydrolysis reactions was found to relieve the negative effect of phenolics. Similarly, hydrolytic activity of a commercial enzyme cocktail Cellic Ctec2 was enhanced in the presence of low concentrations of phenolics.