Feruloylated Wheat Bran Arabinoxylans: Isolation and Characterization of Acetylated and O-2-Monosubstituted Structures

Arabinoxylan structures vary based on the degree and pattern of substitution of the beta-(1 -> 4)-linked D-xylopyranose backbone with alpha-L-arabinofuranose units, acetyl groups, uronic acids, and feruloylated side chains. Substitution differences affect arabinoxylans' physicochemical and physiological characteristics. Wheat bran arabinoxylans were hydrolyzed with GH10 and GH11 endo-1,4-beta-xylanases, and feruloylated oligosaccharides were isolated and purified (Amberlite XAD-2 isolation, Sephadex LH-20 gel permeation chromatography, and preparative reversed-phase HPLC). The pure, isolated compounds were structurally characterized via liquid chromatography-electrospray ionization-mass spectrometry and one-dimensional and two-dimensional NMR analyses. In addition to the well-known products of endo-xylanase hydrolysis (xylotriose and xylobiose O-3-substituted with a 5-O-trans-feruloyl-alpha-arabinofuranosyl unit on the middle and nonreducing xylose residue, respectively), novel structural features, including O-2-monosubstitution of xylose adjacent to a xylose carrying feruloylated arabinose, were observed. Additionally, a simultaneously acetylated and feruloylated oligosaccharide has been isolated and tentatively characterized. Oligosaccharides esterified with caffeic acid were also isolated, but these were proven to result, at least in part, as artifacts of the enzymatic hydrolysis.