Cereal grain arabinoxylans contain a unique non-feruloylated disaccharide side-chain with alpha-xylose units: α-D-xylopyranosyl-(1 → 3)-L-arabinose

Feruloylated side-chain oligosaccharide substituents are a distinctive feature of cereal grains' arabinoxylans (AX), but less is known about non-feruloylated oligosaccharide side-chain substituents. In this study we explored non-feruloylated disaccharide side-chains from corn (Zea mays L.) AX that had not been exposed to alkaline conditions and successfully isolated and unequivocally characterized the structure, α-D-xylopyranosyl-(1 → 3)-L-arabinose. This structure is uniquely different from the oligosaccharide portion of the comparable feruloylated disaccharide compound. Qualitative screening showed that this non-feruloylated disaccharide is also present in wheat (Triticum aestivum L.), oats (Avena sativa L.), and popcorn (Zea mays L. var. everta). β-D-Xylopyranosyl-(1 → 2)-L-arabinose, the carbohydrate motif from feruloylated oligosaccharide side-chain substituents, was not found in a non-feruloylated form. Our data imply that non-feruloylated β-D-xylopyranosyl-(1 → 2)-L-arabinose side-chains may not be an authentic component of cereal AX, and that structural models of AX should be revised accordingly. Non-feruloylated oligosaccharide side-chains are indeed an authentic substituent of cereal AX, but their carbohydrate structures sharply diverge from their feruloylated counterparts.