Delignified Arundo donax was sequentially extracted with DMSO, saturated barium hydroxide, and 1.0 M aqueous
NaOH solution. The yields of the soluble fractions were 10.2, 6.7, and 10.0% (w/w), respectively, of the dry Arundo donax
materials. The DMSO-, Ba(OH)2
- and NaOH-soluble hemicellulosic fractions were further fractionated into two subfractions by
gradient 50% and 80% saturation ammonium sulfate precipitation, respectively. Monosaccharide, molecular weight, FT-IR, and
1D (
1
H and
13
C) and 2D (HSQC) NMR analysis revealed the differences in structural characteristics and physicochemical
properties among the subfractions. The subfractions precipitated with 50% saturation ammonium sulfate had lower arabinose/
xylose and glucuronic acid/xylose ratios but had higher molecular weight than those of the subfractions precipitated by 80%
saturation ammonium sulfate. FT-IR and NMR analysis revealed that the highly acetylated DMSO-soluble hemicellulosic
subfraction (HD50
) could be precipitated with a relatively lower concentration of 50% saturated ammonium sulfate, and thus the
gradient ammonium sulfate precipitation technique could discriminate acetyl and non-acetyl hemicelluloses. It was found that the
DMSO-soluble subfraction HD50
precipitated by 50% saturated ammonium sulfate mainly consisted of poorly substituted Oacetyl arabino-4-O-methylglucurono xylan with terminal units of arabinose linked on position 3 of xylose, 4-O-methylglucuronic
acid residues linked on position 2 of the xylan bone, and the acetyl groups (degree of acetylation, 37%) linked on position 2 or 3.
The DMSO-soluble subfraction HD80
precipitated by 80% saturated ammonium sulfate was mainly composed of highly
substituted arabino-4-O-methylglucurono xylan and β-D-glucan