Carbohydrate structural analysis of wheat flour arabinogalactan protein

Abstract

The water-extractable arabinogalactan protein (AGP) was isolated from bread wheat flour ( Triticum aestivum L. variety Cadenza) and the structure of the arabinogalactan (AG) carbohydrate component was studied. Oligosaccharides, released by hydrolysis of the AG with a range of AGP-specific enzymes, were characterised by Matrix Assisted Laser Desorption Ionisation (MALDI)-Time of Flight (ToF)-Mass Spectrometry (MS), MALDI-ToF/ToF high energy collision induced dissociation (CID) and Polysaccharide Analysis by Carbohydrate gel Electrophoresis (PACE). The AG is composed of a β-(1→3)- d-galactan backbone with β-(1→6)- d-galactan side chains. These side chains are highly variable in length, from one to at least 20 Gal residues and are highly substituted with α- l-Ara f. Single GlcA residues are also present at the non-reducing termini of some short β-(1→6)-galactan side chains. In addition, the β-(1→6)-galactan side chains are also substituted with β- l-Ara p. We propose a polysaccharide structure of the wheat flour AGP that is substantially revised from earlier models.