Submitted to: Metabolites
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2012
Publication Date: 11/19/2012
Citation: Bowman, M.J., Dien, B.S., O'Bryan, P.J., Sarath, G., Cotta, M.A. 2012. Comparative analysis of end point enzymatic digests of arabino-xylan isolated from switchgrass (Panicum virgatum L) of varying maturities using LC-MS(n). Metabolites. 2(4):959-982.
Interpretive Summary: Switchgrass is a perennial grass presently used as forage and being developed as a bioenergy crop for conversion to biofuels. Up to 50% of the switchgrass cell wall and associated carbohydrates are xylan. Switchgrass was analyzed for xylan structural features at variable harvest maturities where differences in conversion were observed. It was found that the structural features of xylan do not change during maturity, rather the proportions of xylan change. This indicates that enzymatic combinations capable of hydrolyzing xylan will be effective regardless of maturity. Furthermore, the analytical methods developed will allow for screening of enzymes for beneficial selectivities for bioconversion.
Technical Abstract: Switchgrass (Panicum virgatum L., SG) is a perennial grass presently used for forage and being developed as a bioenergy crop for conversion of cell wall carbohydrates to biofuels. Up to 50% of the cell wall associated carbohydrates are xylan. SG was analyzed for xylan structural features at variable harvest maturities. Xylan from each of 3 maturities was isolated using classical alkaline extraction to yield fractions (Xyl A and B) with varying compositional ratios. The Xyl B fraction was observed to decrease with plant age. Xylan samples were subsequently prepared for structure analysis by digesting with pure endo-xylanase, which preserved side-groups, or a commercial carbohydrase preparation favored for biomass conversion work. Enzymatic digestion products were successfully permethylated and analyzed by reverse-phase liquid chromatography with mass spectrometric detection (RP-HPLC-MSn). This method is advantageous compared to prior work on plant biomass because it avoids isolation of individual arabinoxylan oligomers. The use of RP-HPLC-MSn differentiated 14 structural oligosaccharides (d.p. 3-9) from the monocomponent enzyme digestion and 9 oligosaccharide structures (d.p. 3-9) from hydrolysis with a cellulase enzyme cocktail. The distribution of arabinoxylan oligomers varied depending upon the enzyme(s) applied but did not vary with harvest maturity.