Molecular dimensions and structural features of neutral polysaccharides from the seed mucilage of Hyptis suaveolens L

Abstract

The seed mucilage of Hyptis suaveolens L. includes acid - and neutral heteropolysaccharides in a ratio of about 1:1. The anionic charged fraction responsible for swelling and viscous behaviour possesses an average molar mass of Mw=350kg/mol, Mn=255kg/mol. The neutral polysaccharide fraction shows an average molar mass of Mw=47kg/mol and Mn=28kg/mol and is composed of d-Galp-, d-Glcp- and d-Manp residues in a molar ratio of about 3:2:1. The structural features present galactoglucan (30%) and galactoglucomannan (70%) with a high level of terminal β-linked d-Galp residues (18%). Structural details of galactoglucomannan are derived by combined enzymatic and chemical methods as well as NMR spectroscopy. Sequences of octa/nonasaccharide β-d-Glcp-(1→4)[β-d-Galp-(1→2)-α-d-Galp-(1→6)]-β-d-Manp-(1→4)-β-d-Glcp-(1→4)-β-d-Glcp-(1→4)[β-d-Galp-(1→2)-α-d-Galp-(1→6)]-β-d-Manp and lower mass tetrasaccharide repeating units β-d-Glcp-(1→4)[β-d-Galp-(1→2)-α-d-Galp-(1→6)]-β-d-Manp were found. The level of the prebiotic activity is related to the availability of β-linked d-Galp residues in the side chains of the molecules.

Keywords: Galactoglucan; Galactoglucomannan; Hyptis suaveolens L.; Methylation analysis; Mucilage; NMR spectroscopy; Polysaccharide.