Partial acid-hydrolysis of TEMPO-oxidized arabinoxylans generates arabinoxylan-structure resembling oligosaccharides

Carolina O Pandeirada,Sofia Speranza,Edwin Bakx,Yvonne Westphal,Hans-Gerd Janssen,Henk A Schols

doi:10.1016/j.carbpol.2021.118795

Carolina O Pandeirada, Sofia Speranza + Show 4 more

Open Access

https://doi.org/10.1016/j.carbpol.2021.118795

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Abstract

Arabinoxylans (AXs) display biological activities that depend on their chemical structures. To structurally characterize and distinguish AXs using a non-enzymatic approach, various TEMPO-oxidized AXs were partially acid-hydrolysed to obtain diagnostic oligosaccharides (OS). Arabinurono-xylo-oligomer alditols (AUXOS-A) with degree of polymerization 2–5, comprising one and two arabinuronic acid (AraA) substituents were identified in the UHPLC-PGC–MS profiles of three TEMPO-oxidized AXs, namely wheat (ox-WAX), partially-debranched WAX (ox-pD-WAX), and rye (ox-RAX). Characterization of these AUXOS-A highlighted that single-substitution of the Xyl unit preferably occurs at position O-3 for these samples, and that ox-WAX has both more single substituted and more double-substituted xylose residues in its backbone than the other AXs. Characteristic UHPLC-PGC–MS OS profiles, differing in OS abundance and composition, were obtained for each AX. Thus, partial acid-hydrolysis of TEMPO-oxidized AXs with analysis of the released OS by UHPLC-PGC-MS is a promising novel non-enzymatic approach to distinguish AXs and obtain insights into their structures.

Highlights

There is a high interest in dietary fibres due to their associated health benefits (Stephen et al, 2017)
Pericarp AXs from wheat are reported to have the highest degree of double-substituted Xyl units (Maes & Delcour, 2002), and water extractable AXs (WEAX) from rye have a higher degree of singlesubstituted Xyl units than the corresponding WEAX from wheat (Buksa, Praznik, Loeppert, & Nowotna, 2016; Migliori & Gabriele, 2010)
Having an identical Ara:Xyl ratio, rye AX (RAX) displayed a higher degree of branching (DB) than wheat flour AX (WAX) (47% and 39%, respectively, Table 1), which is due to different levels of single- and double-substitution of the Xyl units between samples

Summary

Introduction

There is a high interest in dietary fibres due to their associated health benefits (Stephen et al, 2017). Among the various chromatographic methods used to characterize OS, such as high performance anion-exchange chromatography (HPAEC) and hydrophilic interaction liquid chromatography (HILIC) (Leijdekkers, Sanders, Schols, & Gruppen, 2011; Van Gool et al, 2011; Westphal, Schols, Voragen, & Gruppen, 2010a), porous graphitic carbon (PGC) chromatography has shown the ability to successfully separate neutral and acidic oligosaccharide isomers (Borewicz et al, 2019; Gu, Wang, Beijers, de Weerth, & Schols, 2021; Logtenberg et al, 2020; Veillon et al, 2017). A non-enzymatic approach consisting of partial acidhydrolysis of various TEMPO-oxidized (ox-)AXs followed by analysis of the released fragments using UHPLC-PGC-MS is proposed to obtain characteristic chromatographic OS profiles for ox-AX structure investi gation. Structural character ization of the released OS is used to obtain an insight into the structure of the native AX

Materials

Sugar composition analysis by HPAEC-PAD

Glycosidic linkage analysis

Molecular weight distribution by HPSEC-RI

Oligosaccharides profile and characterization by UHPLC-PGC-MS

Results and discussion