Structures of enzymically derived oligosaccharides from sorghum glucuronoarabinoxylan

Oligosaccharides derived from alkali-extracted sorghum glucuronoarabinoxylan by digestion with a combination of (1→4)-β-d-arabinoxylan arabinofuranohydrolase (AXH) and endo-(1→4)-β-d-xylanase (Xyl I), both from Aspergillus awamori, were purified by size-exclusion chromatography followed by preparative high-performance anion-exchange chromatography. Structural studies including monosaccharide analysis, methylation analysis, 1H NMR spectroscopy, and mass spectrometry were carried out, resulting in the characterisation of four novel oligosaccharides, namely, α-d-GlcpA-(1→2)-β-d-Xylp-(1→4)-β-d-Xylp-(1→4)-β-d-Xylp, α-d-GlcpA-(1→2)-β-d-Xylp-(1→4)[α-l-Araf-(1→3)]-β-d-Xylp-(1→4)-β-d-Xylp, α-d-GlcpA-(1→2)-β-d-Xylp-(1→4)-β-d-Xylp-(1→4)[α-l-Araf-(1→2)-α-l-Araf-(1→3)]-β-d-Xylp-(1→4)-β-d-Xylp, and α-d-GlcpA-(1→2)-β-d-Xylp-(1→4)[α-l-Araf-(1→3)]-β-d-Xylp-(1→4)[α-l-Araf-(1→2)-α-l-Araf-(1→3)]-β-d-Xylp-(1→4)-β-d-Xylp. The various oligosaccharides identified provide additional insight into the structure of sorghum glucuronoarabinoxylan. Furthermore, novel data were generated with respect to the substrate specificity of AXH and Xyl I towards glucuronoarabinoxylans in general.