title: The fate of lignin during hydrothermal pretreatment.
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.
authors.affiliation: 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.|Current address: Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, British Columbia V6T 1Z3, Canada.|BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
authors.forename: Heather L
authors.initials: HL
authors.lastname: Trajano
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.|BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Engle
authors.affiliation: School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th Street N.W., Atlanta, GA 30332, USA.|Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, 1 Brookings Drive, Saint Louis, MO 63130, USA.|BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
authors.forename: Marcus
authors.initials: M
authors.lastname: Foston
authors.affiliation: School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th Street N.W., Atlanta, GA 30332, USA.|BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Ragauskas
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.|BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Tschaplinski
authors.affiliation: 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.|BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Wyman
references.citation: Biotechnol Bioeng. 2008 Dec 1;101(5):913-25
references.pmid: 18781690
references.citation: J Am Chem Soc. 2011 Dec 21;133(50):20277-87
references.pmid: 22035184
references.citation: Planta. 2007 Jun;226(1):267-81
references.pmid: 17333255
references.citation: Bioresour Technol. 2008 Jun;99(9):3424-30
references.pmid: 17881227
references.citation: Science. 2009 Apr 3;324(5923):89-91
references.pmid: 19342588
references.citation: Biotechnol Prog. 2007 Nov-Dec;23(6):1333-9
references.pmid: 17973399
references.citation: Appl Biochem Biotechnol. 2010 Sep;162(1):62-74
references.pmid: 19701727
references.citation: Biomacromolecules. 2010 Sep 13;11(9):2329-35
references.pmid: 20726544
references.citation: Bioresour Technol. 2007 Nov;98(16):3061-8
references.pmid: 17141499
references.citation: Int J Biol Macromol. 2001 Jul 19;29(1):45-51
references.pmid: 11429188
references.citation: Bioresour Technol. 2005 Apr;96(6):673-86
references.pmid: 15588770
references.citation: Phytochemistry. 2007 Aug;68(15):2118-25
references.pmid: 17582447
references.citation: Biotechnol Biofuels. 2012 Jan 04;5(1):2
references.pmid: 22214220
references.citation: Biotechnol Biofuels. 2008 Apr 16;1(1):5
references.pmid: 18471316
references.citation: Magn Reson Chem. 2007 Jan;45(1):37-45
references.pmid: 17080511