Chemical structure and rheological studies of arabinoglucuronoxylans from the Cercidium praecox exudate brea gum.

The structure of the arabinoglucuronoxylans from brea gum was elucidated through an chemical and NMR spectroscopical analysis. They are composed of xylose, arabinose, glucuronic acid and 4-O-methylglucuronic acid in a molar ratio 1:0.44:0.16:0.22. The structure consists of a central chain of (1→4)-β-d-xylopyranose of which ca.70% are susbstituted in C2 with single stubs of others sugars (β-d-Xylp, α-d-GlcpA and 4-O-Me-α-d-GlcpA), with disaccharides (α-l-Arap-(1→2)-4-O-Me-α-d-GlcpA-(1→, α-l-Arap-(1→2)-α-d-GlcpA-(1→, β-l-Araf-(1→3)-α-l-Araf-(1→ and α-l-Araf-(1→3)-α-l-Araf-(1→5), and possibly with trisaccharides of xylose. The determination of the location of the acetyl groups and their quantification in these arabinoglucuronoxylans has been achieved for the first time. Brea gum presents a higher thickening effect than gum arabic in 5% aqueous solution, demonstrating its potential usefulness for food and pharmaceutical applications.