Determination of the xylan backbone distribution of arabinoxylan-oligosaccharides

Arabinoxylan-oligosaccharide samples (AXOS) present themselves as mixtures of different molecular entities with xylan backbones of different length and with different levels of arabinose substitution. Their prebiotic properties depend on their degree of polymerisation (DP) and degree of arabinose substitution (DAS). Therefore, structural characterisation of AXOS samples is important. Gas chromatography (GC) is most frequently used for quantification of AXOS levels and for determination of the average DP (avDP) and average DAS (avDAS), yet it does not provide information on the molecular mass distribution of the xylan backbones of the different AXOS entities present in the mixture. This manuscript evaluates a method based on high performance anion exchange chromatography (HPAEC) involving quantification of xylo-oligosaccharides (XOS) after either acidic or enzymic removal of arabinose substituents for its ability to determine such distribution. Results show that despite the fact that a small fraction of the arabinoses could not be removed, representative DP distributions of xylan backbones in complex AXOS samples were obtained. The similarity of the avDP determined with GC or determined with the new HPAEC method using enzymic removal of arabinose substituents confirmed this. It can be concluded that the HPAEC method involving enzymic removal of arabinoses provides useful insight in the DP distribution of the xylan backbones in complex AXOS samples.

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