ARS | Publication request: Chemical depolymerization of switchgrass xylan with oligosaccharide product analysis by HPAEC-PAD and mass spectrometry

Submitted to: Biotechnology for Fuels and Chemicals Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 22, 2010
Publication Date: April 22, 2010
Citation: Bowman, M.J., Dien, B.S., O Bryan, P.J., Sarath, G., Cotta, M.A. 2010. Chemical depolymerization of switchgrass xylan with oligosaccharide product analysis by HPAEC-PAD and mass spectrometry [abstract]. Biotechnology for Fuels and Chemicals. p. 73.

Technical Abstract: Xylan is a barrier to enzymatic hydrolysis of plant cell walls. It is well accepted that the xylan layer needs to be removed to efficiently hydrolyze cellulose and consequently pretreatment conditions are in part optimized for maximal xylan depolymerization or displacement. Xylan consists of a long chain of beta(1,4) linked xylose units substituted with arabinose (usually alpha(1,3) in grasses) and glucuronic acid (alpha(1,2)). Arabinose units can be further substituted with acids (acetic, uronic, and phenolic acids) and galactose. It has been proposed that the substitutions are not random along the xylan chains but rather occur as domain structures; such domains have been postulated for xylans isolated from wheat, barley, and rye pericarps. It is hypothesized that these domains occur in specific patterns suggesting they have a structural function and therefore may play a role in determining reactivity of xylan to pretreatment. Analysis of intact xylan is problematic because of its chain length and heterogeneous side groups; therefore, we explored conditions to partially hydrolyze the xylan and separate the resultant multimeric fragments by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) to determine conditions producing a distribution of arabinoxylooligomers. In order to minimize the disruption to domain structures, various conditions were investigated to maximize the number of informative oligosaccharides (i.e., with branches intact) generated. Mass spectrometric analysis was employed to determine the structures of the resultant oligosaccharides via their fragmentation patterns. Traditional alkaline extracted switchgrass xylan samples were used in this study.