Investigation of the distribution of arabinose residues on the xylan backbone of water-soluble arabinoxylans from wheat flour

Homogeneous water-soluble non-feruloylated arabinoxylan fractions from wheat flour (cv. Soissons) have been studied for their fine structure. Arabinosyl residue distribution on arabinoxylan chains was investigated through periodate oxidation and enzymic hydrolysis methods. A double oxidation and reduction sequence was used to effect complete oxidation of arabinoxylans and an hydrolysis time of 180 min was used for Smith degradation with HCl 0.02 M at 100 °C. Periodate oxidation, reduction and mild acid hydrolysis produced xylosides containing up to six residues. Analysis by HPAEC of the xylosides liberated by mild acid hydrolysis revealed that an increase in arabinose to xylose ratio is expressed on the polymer by an increase in length of substituted regions and greater proportions of them. Enzymic hydrolysis with a xylanase from Aspergillus aculeatus of lowly and highly substituted fractions revealed great differences in degradation extent. Random distribution of arabinose residues along the xylan backbone was computed and compared to experimental results.