Structural elucidation of hemicelluloses from Vetiver grass

Structure of the hemicelluloses extracted from Vetiver grass (Vetiveria zizanioides Nash) leaves was studied. The monosaccharide compositions and the position of the linkages between monosaccharides in the hemicelluloses were defined by TFA hydrolysis and methylation analysis, respectively. 13C NMR and FT-IR spectroscopic methods gave details of the anomeric linkage configuration and confirmed the structure of the hemicelluloses. The proposed structure of the hemicelluloses from the Vetiver grass is an arabinoxylan mainly consisting of (1→4)-β-d-xylan backbone substituted in O-2 and/or O-3 by single α-l-arabinose residue, single α-d-glucuronic acid residue and/or short chains of sugar residues containing arabinose, xylose and galactose. In addition, the (1→4)-linked β-d-xylopyranosyl residues in the backbone may contain substituted phenolic acids (e.g. ferulic acid and p-coumaric acid). The substituted phenolic acids are esterified via their carboxyl groups to the C-5 hydroxyl of the α-l arabinofuranosyl residues in side chain.