Chemical characterisation of polysaccharides from Lilium davidii

Abstract

Lilium davidii var. unicolor Salisb is known for its esculent and exceptionally sweet bulbs. This article reports the isolation and purification of a non-starch polysaccharide from the bulb tissues. The polysaccharide was fractionated by Sephadex G-100 column chromatography, giving two polysaccharide fractions. We collected the main peak polysaccharide, termed Lilium davidii polysaccharide (LDP). The molecular appearance of LDP at different concentrations was observed with atomic force microscopy (AFM) imaging, and the chemical characterisation of LDP was studied by physical, chemical and spectroscopic techniques: for example, differential scanning calorimetry (DSC) analysis, methylation analysis, GC, GC-MS, and NMR. The results demonstrate that the LDP is an amorphous powder, containing three monosaccharide molecules: D-mannose (D-Man), D-glucose (D-Glc) and D-galactose (D-Gal), with approximate molar ratios of 10 : 19 : 1. The morphology of LDP was arranged as irregular crumb-like or island forms (3-D images) when the concentration of the solution was low, and more molecules were entangled as a rugged sugar layer at high concentration. The LDP has a molecular weight of 5.17 × 10⁴ g mol⁻¹. On the basis of methylation and GC-MS analysis, IR, NMR, the likely linkages of sugar components of LDP was described as follows: the main chain of the LDP is primarily made up of a 1,4-linked form for β-Glc and a 1,3-linked form for α-Man with molar ratios of 2 : 1. On average, there is one 1,6-linked form for α-Gal or one 1,3-linked form for α-Man residues which can be substituted at 6-O from among 30 sugar residues. The reduction terminal is β-Glc.

Keywords:

• Lilium davidii polysaccharide
• AFM image
• structural analysis
• NMR spectroscopy