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Biotechnol Biofuels. 2013 Aug 1;6(1):110. doi: 10.1186/1754-6834-6-110.

The fate of lignin during hydrothermal pretreatment.

Author information

1
Department of Chemical and Environmental Engineering and Center for Environmental Research and Technology, Bourns College of Engineering, University of California Riverside, 1084 Columbia Ave, Riverside, CA 92507, USA.
2
Current address: Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, British Columbia V6T 1Z3, Canada.
3
BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
4
Biosciences Division, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
5
School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th Street N.W., Atlanta, GA 30332, USA.
6
Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, Saint Louis, MO 63130, USA.
#
Contributed equally

Abstract

BACKGROUND:

Effective enzymatic hydrolysis of lignocellulosic biomass benefits from lignin removal, relocation, and/or modification during hydrothermal pretreatment. Phase transition, depolymerization/repolymerization, and solubility effects may all influence these lignin changes. To better understand how lignin is altered, Populus trichocarpa x P. deltoides wood samples and cellulolytic enzyme lignin (CEL) isolated from P. trichocarpa x P. deltoides were subjected to batch and flowthrough pretreatments. The residual solids and liquid hydrolysate were characterized by gel permeation chromatography, heteronuclear single quantum coherence NMR, compositional analysis, and gas chromatography-mass spectrometry.

RESULTS:

Changes in the structure of the solids recovered after the pretreatment of CEL and the production of aromatic monomers point strongly to depolymerization and condensation being primary mechanisms for lignin extraction and redeposition. The differences in lignin removal and phenolic compound production from native P. trichocarpa x P. deltoides and CEL suggested that lignin-carbohydrate interactions increased lignin extraction and the extractability of syringyl groups relative to guaiacyl groups.

CONCLUSIONS:

These insights into delignification during hydrothermal pretreatment point to desirable pretreatment strategies and plant modifications. Because depolymerization followed by repolymerization appears to be the dominant mode of lignin modification, limiting the residence time of depolymerized lignin moieties in the bulk liquid phase should reduce lignin content in pretreated biomass. In addition, the increase in lignin removal in the presence of polysaccharides suggests that increasing lignin-carbohydrate cross-links in biomass would increase delignification during pretreatment.

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