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Open Access Review

Assessing the molecular structure basis for biomass recalcitrance during dilute acid and hydrothermal pretreatments

Yunqiao Pu14, Fan Hu24, Fang Huang24, Brian H Davison34 and Arthur J Ragauskas124*

Author Affiliations

1 Institute of Paper Science and Technology, Georgia Institute of Technology, Atlanta, GA, USA

2 BioEnergy Science Center, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, USA

3 Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA

4 BioEnergy Science Center, Oak Ridge, TN, USA

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Biotechnology for Biofuels 2013, 6:15  doi:10.1186/1754-6834-6-15

Published: 28 January 2013

Abstract

The production of cellulosic ethanol from biomass is considered a promising alternative to reliance on diminishing supplies of fossil fuels, providing a sustainable option for fuels production in an environmentally compatible manner. The conversion of lignocellulosic biomass to biofuels through a biological route usually suffers from the intrinsic recalcitrance of biomass owing to the complicated structure of plant cell walls. Currently, a pretreatment step that can effectively reduce biomass recalcitrance is generally required to make the polysaccharide fractions locked in the intricacy of plant cell walls to become more accessible and amenable to enzymatic hydrolysis. Dilute acid and hydrothermal pretreatments are attractive and among the most promising pretreatment technologies that enhance sugar release performance. This review highlights our recent understanding on molecular structure basis for recalcitrance, with emphasis on structural transformation of major biomass biopolymers (i.e., cellulose, hemicellulose, and lignin) related to the reduction of recalcitrance during dilute acid and hydrothermal pretreatments. The effects of these two pretreatments on biomass porosity as well as its contribution on reduced recalcitrance are also discussed.

Keywords:
Biomass recalcitrance; Dilute acid pretreatment; Hydrothermal pretreatment; Cellulose structure; Structural transformation