title: Investigation of lignin deposition on cellulose during hydrothermal pretreatment, its effect on cellulose hydrolysis, and underlying mechanisms.
abstract: In dilute acid pretreatment of lignocellulosic biomass, lignin has been shown to form droplets that deposit on the cellulose surface and retard enzymatic digestion of cellulose (Donohoe et al., 2008; Selig et al., 2007). However, studies of this nature are limited for hydrothermal pretreatment, with the result that the corresponding mechanisms that inhibit cellulosic enzymes are not well understood. In this study, scanning electron microscope (SEM) and wet chemical analysis of solids formed by hydrothermal pretreatment of a mixture of Avicel cellulose and poplar wood showed that lignin droplets from poplar wood relocated onto the Avicel surface. In addition, nuclear magnetic resonance (NMR) showed higher S/G ratios in deposited lignin than the initial lignin in poplar wood. Furthermore, the lignin droplets deposited on Avicel significantly impeded cellulose hydrolysis. A series of tests confirmed that blockage of the cellulose surface by lignin droplets was the main cause of cellulase inhibition. The results give new insights into the fate of lignin in hydrothermal pretreatment and its effects on enzymatic hydrolysis.
authors.affiliation: Department of Chemical and Environmental Engineering, Bourns College of Engineering, University of California, Riverside, California, 92507; Center for Environmental Research and Technology (CE-CERT), University of California, Riverside, California; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
authors.forename: Hongjia
authors.initials: H
authors.lastname: Li
authors.forename: Yunqiao
authors.initials: Y
authors.lastname: Pu
authors.forename: Rajeev
authors.initials: R
authors.lastname: Kumar
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Ragauskas
authors.forename: Charles E
authors.initials: CE
authors.lastname: Wyman
mesh_terms: D044602:Cellulases / Q000378:metabolism*; D002482:Cellulose / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects / Q000648:ultrastructure; D006358:Hot Temperature; D006868:Hydrolysis; D008031:Lignin / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects / Q000648:ultrastructure; D009682:Magnetic Resonance Spectroscopy; D008855:Microscopy, Electron, Scanning; D032107:Populus; D014934:Wood
chemical_list: D002482:Cellulose; D008031:Lignin; D044602:Cellulases
keywords: deposition; enzymatic hydrolysis; hydrothermal pretreatment; inhibition mechanisms; lignin droplets