Presence of 1→3-linked 2-O-β-d-xylopyranosyl-α-l-arabinofuranosyl side chains in cereal arabinoxylans

The presence of a fairly uncommon side chain 2-O-β-d-xylopyranosyl-α-l-arabinofuranosyl in arabinoxylans (AX) from eight different cereal by-products was investigated, using 1H NMR spectroscopy and high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) after Shearzyme® (GH10 endo-1,4-β-d-xylanase) hydrolysis. This disaccharide side group was present in significant amounts in AX extracted from corn cobs and barley husks. For the first time, it was also detected in AX from oat spelts and rice husks, and in lesser amounts in wheat straw AX. Arabinoxylo-oligosaccharide (AXOS) containing the 2-O-β-d-Xylp-α-l-Araf side chain was purified from the oat spelt AX hydrolysate and the structure was fully analyzed using 1D and 2D NMR spectroscopy. The AXOS was identified as β-d-Xylp-(1→2)-α-l-Araf-(1→3)-β-d-Xylp-(1→4)-d-Xyl. To our knowledge, such a structure with 2-O-β-d-Xylp-α-l-Araf attached to the O-3 of the nonreducing end of xylobiose has not been described previously. New information on substitution of AX from various cereal by-products was obtained by combining NMR and enzyme-assisted HPAEC-PAD analysis.