Binary additives for in-situ mitigating the inhibitory effect of lignin-derived phenolics on enzymatic hydrolysis of lignocellulose: Enhanced performance and synergistic mechanism

Separation-free sugar-platform biorefinery from lignocellulose has drawn increasing attention due to its feasibility. However, the presence of lignin-derived phenolics within the whole slurry after pretreatment, is highly inhibitory toward enzymatic hydrolysis of lignocellulose especially at high solid loadings. Developing effective methods to mitigate the phenolics-caused enzyme inhibition in-situ can further improve the cellulose hydrolysis, while the relevant studies are limited. In this study, the effects of different kinds of additives on mitigating the phenolic-caused inhibition was determined and the synergy among the additives were systematically evaluated. Based on the analysis, we developed novel binary additives to alleviate the phenolic-caused inhibition of cellulose hydrolysis in-situ. In addition to surfactants, a reducing agent (l-cysteine) was introduced to enhance the enzymatic hydrolysis of cellulose and the strong synergism between the reducing agent and the surfactant was firstly demonstrated. Further, the mechanism study indicated that these additives could prevent the strong interactions between phenolics and cellulase and improve the major cellulase activities. Finally, with the addition of the binary additives, the cellulose hydrolysis for acid/alkaline pretreated corn stover were significantly improved with low enzyme loading without detoxification. This study provides directions for designing novel additives to improve the enzymatic hydrolysis of pretreated lignocellulosic biomass.