Structural elucidation of a water-soluble polysaccharide isolated from Balangu shirazi (Lallemantia royleana) seeds

Abstract

A novel water-soluble polysaccharide was isolated from the seeds of Balangu shirazi (BSG) by warm-water extraction and then purified. The BGG contained 8.2% moisture, 13.1% ash, 1.6% protein and 77.1% carbohydrate. However, no lipid content was observed. Elemental analysis of the gum indicated BSG had a carbon, hydrogen, oxygen and nitrogen content of 33.39%, 4.05%, 35.45% and 0.31%, respectively. The FT-IR spectroscopy revealed the major functional groups consisted of (OH), (C-H) and (-COO-), and BSG was comprised of pyranose-form sugars with both α-and β-configurations. Monosaccharide composition analysis by GC-MS showed the BSG contained sugar constituents of arabinose, rhamnose, mannose, fructose, galactose, α-and β-d-glucose, glucuronic acid, galacturonic acid, and glucosamine although mainly composed of rhamnose, galactose, arabinose and galacturonic acid. 1H, 13C and COSY NMR spectroscopy demonstrated the presence of (1 → 4)-linked-α-D-GalpA, (1 → 3)-linked-β-D-Galp, (1 → 6)-linked-β-D-Galp, (1 →)-β-L-Arap, (1 → 2)-linked-α-L-Rhap and (1 → 3)-linked-β-L-Arap in the polysaccharide sequence.