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Title
Structural characterization of hemicelluloses from bamboo culms (Neosinocalamus Affinis)
Authors
S.N. SUN T.Q. YUAN M.F. LI X.F. CAO F. XU and Q.Y. LIU
Received
November 21, 2011
Published
Volume 46, Issue 3-4 March-April
Keywords
bamboo culms, hemicelluloses, structural characterization, xylan, NMR
Abstract
Dewaxed bamboo culms (Neosinocalamus affinis) were sequentially extracted with distilled water and 70% ethanol at 80 ºC for 3 h, 0.2 and 0.5 M NaOH, 70% ethanol containing 0.6 M NaOH, and 1.0 and 2.0 M NaOH at 50 ºC for 3 h using a solid to liquid ratio of 1:25 (g/mL). The hemicellulosic fractions obtained were characterized by high performance anion exchange chromatography (HPAEC), gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, 1H and 13C nuclear magnetic resonance (NMR), and 2D heteronuclear single quantum coherence (HSQC) NMR spectroscopies. Compared to the water-soluble fraction, the alkali-soluble hemicelluloses primarily consisted of xylose (73.5-92.7%), and had a more linear structure and larger macromolecules, evidenced by Xyl/Ara ratios (11.0-22.9) and higher average molecular weights (? = 41200-68770 g/mol). Increasing the alkaline w concentrations from 0.2 to 2.0 M NaOH decreased the molecular weights from 68770 to 42790 g/mol, but increased the Xyl/Ara ratios from 11.0 to 22.9 in the hemicellulosic fractions. The fractions isolated with 0.5 and 1.0 M NaOH were found to be composed of a linear (1?4)-?-D-xylopyranosyl main chain substituted by a small amount of L-arabinofuranosyl at C-2 and/or C-3 together with a minor quantity of 4-O-methylglucuronic acid at C-2, representing typical polysaccharide structure in bamboo.
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