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.
| Original language | English |
|---|---|
| Article number | 110 |
| Journal | Biotechnology for Biofuels |
| Volume | 6 |
| Issue number | 1 |
| DOIs | |
| State | Published - 2013 |
Funding
We thank the Office of Biological and Environmental Research in the DOE Office of Science for supporting this work through the BioEnergy Science Center (BESC). BESC is a U.S. Department of Energy Bioenergy Reseach Center supported by the Office of Biological and Environmental Research in the DOE Office of Science. This manuscript has been co-authored by a contractor of the U.S. Government under contract DE-AC05-00OR22725. We also wish to thank Dr. Shilin Cao, previously at the School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology and now at the College of Material Engineering at Fujian Agriculture and Forestry University, for preparing the cellulolytic enzyme lignin for this study. We acknowledge support by the Ford Motor Company for the Chair in Environmental Engineering at the University of California Riverside (UCR) that augments our ability to perform such research.
| Funders | Funder number |
|---|---|
| BioEnergy Science Center | |
| U.S. Department of Energy Bioenergy Reseach Center | |
| Office of Science | |
| Biological and Environmental Research |
Keywords
- Condensation
- Depolymerization
- Flowthrough pretreatment
- Hydrothermal pretreatment
- Lignin-carbohydrate complex
- Phase transition
