(535g) Quantification of Wheat Straw Lignin by Comprehensive NMR Techniques

Quantification of wheat straw lignin by comprehensive
NMR techniques

Jijiao
Zeng¹, Greg Helms² and Shulin Chen^1*

1. Department of Biological Systems
Engineering, Washington State University, Pullman, Washington 99164-6120, USA

2. Department of Chemistry, center
for NMR spectroscopy, Washington State University, Pullman, Washington 99164-6120,
USA

^*Corresponding
author. Tel: +1 509 335 3743; fax: +1 509 335 2722.

E-mail address: chens@wsu.edu

Abstract:

Lignin
is secondary natural organic compositions of plant cell wall besides cellulose
and hemicelluse. Structurally lignin is linked with hemicelluloses and
cellulose to form recalcitrant complex that resist the environmental stress. Aiming
to increase efficiency of carbohydrate saccharification, many efforts have been
made to remove and/or modify lignin moieties. However, due to limitation of our
knowledge on detection and quantification of lignin unit at structural level, the
relationship between structural changes and influence on cellulase after these
processes is still unclear. In order to provide complete structural information
of lignin units, a quantitative method was developed to characterize wheat
straw lignin subunits by combination of quantitative ¹³C NMR and
HSQC 2D NMR techniques. Milled wood lignin (MWL) and cellulolytic enzyme-treated
lignin (CEL) was isolated from wheat straw and characterized by 500 MHz NMR
spectrometer. In addition to common syringyl, guaiacyl and p-hydroxyphenol
units, various units and side chains including b-O-4, dibenzodioxocin,
phenylcoumaran, pinoresinol, spirodienone ferrulate, coumarate and p-benzonate
were identified and quantified. The results also showed that CEL contained more
lignin-carbohydrate linkages (LCC) and polysaccharide anomeric compared to MWL.
Moreover, the increased amount of ferrulate in CEL illustrated that wheat straw
lignin was cross-linked with polysaccharides by ferrulate unit which may limit
polysaccharide digestibility in non-woody biomass. p-benzonate and p-coumarate
are both identified as acetylated group in ¦Ã-position of lignin side chains.
The approach taken and the information obtained in the study will provide
useful information for elucidating mechanisms of pretreatment technologies in
terms of changes caused to lignin units.