Structural characterization of (1→2)-β-xylose-(1→3)-α-arabinose-containing oligosaccharide products of extracted switchgrass (Panicum virgatum, L.) xylan after exhaustive enzymatic treatment with α-arabinofuranosidase and β-endo-xylanase.

Switchgrass (Panicum virgatum, L.) is a potential dedicated biomass crop for use in biocatalytic conversion systems to biofuels. Nearly 30% of switchgrass cell wall material is xylan. The complete depolymerization of xylan is desirable both as an additional carbon source for microbial fermentation and to reduce inhibitory effects xylooligomers may have on cellulolytic glycoside hydrolase enzymes. To identify structural features of switchgrass xylan that are not distinguishable by mass spectrometry alone, a α-arabinofuranosidase enzyme was used to remove the arabinose side chains from alkali-extracted switchgrass xylan from three cultivars with simultaneous hydrolysis by β-endo-xylanase to enrich for oligosaccharide products with extended branching. The two most abundant enzymatic digestion products were separated and characterized by LC-MS(n), linkage analysis, and NMR. These two oligosaccharides were present in all three switchgrass cultivars and found to contain (1→2)-β-xylose-(1→3)-α-arabinose side chains, a linkage not previously reported in switchgrass.