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, 1 H NMR spectroscopy, and mass spectrometry were carried out, resulting in the characterisation of four novel oligosaccharides, namely, α- d-Glc pA-(1→2)- β- d-Xyl p-(1→4)- β- d-Xyl p-(1→4)- β- d-Xyl p, α- d-Glc pA-(1→2)- β- d-Xyl p-(1→4)[ α- l-Ara f-(1→3)]- β- d-Xyl p-(1→4)- β- d-Xyl p, α- d-Glc pA-(1→2)- β- d-Xyl p-(1→4)- β- d-Xyl p-(1→4)[ α- l-Ara f-(1→2)- α- l-Ara f-(1→3)]- β- d-Xyl p-(1→4)- β- d-Xyl p, and α- d-Glc pA-(1→2)- β- d-Xyl p-(1→4)[ α- l-Ara f-(1→3)]- β- d-Xyl p-(1→4)[ α- l-Ara f-(1→2)- α- l-Ara f-(1→3)]- β- d-Xyl p-(1→4)- β- d-Xyl p. 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.