What Are the Major Components in Steam Pretreated Lignocellulosic Biomass That Inhibit the Efficacy of Cellulase Enzyme Mixtures?

Any pretreat process used on lignocellulosic substrates, such as steam pretreatment, although opening up and enhancing access to the cellulose, will typically generate inhibitory compounds (i.e., soluble mono/oligomeric sugars, phenolics, furans, extractives, etc.) that limit or restrict the efficiency of enzyme mediated cellulose hydrolysis. In the work reported here, the major groups of inhibitors derived from various, real-life steam pretreated lignocellulosic biomass were identified and their inhibitory effects on the rate and extent of enzymatic hydrolysis were assessed. It was apparent that monomeric sugars and phenolics inhibited the hydrolytic potential of the cellulases most severely, with sugar accounting for the majority of the decrease. The inhibitory effect of the monomeric sugars was consistent and concentration (but not composition) dependent throughout the time course of hydrolysis. In contrast, the influence of the phenolics was substrate dependent and more harmful at the later stage of hydrolysis. Surprisingly, the oligomeric sugars derived after steam pretreatment of woody biomass showed little influence on the hydrolytic potential of cellulase enzymes.