Non-starch polysaccharides from American ginseng: physicochemical investigation and structural characterization

Non-starch polysaccharides (GSP) from roots of American ginseng were extracted and purified. The physicochemical properties and detailed structure of GSP was systematically studied using high performance size-exclusion chromatography (HPSEC), Fourier transform infrared spectroscopy (FTIR), methylation analysis and 1D & 2D NMR spectroscopy. Weight average molecular weight (Mw) and intrinsic viscosity of GSP was 85.4 kDa and 0.41 dL/g, respectively. Monosaccharide composition analysis indicated that GSP consisted of rhamnose, arabinose, galactose, glucose and uronic acid with a weight ratio of 1:4:8:8:50. The dominate component in GSP was galacturonic acid (up to 70% in molar ratio) based on methylation analysis. FTIR demonstrated that GSP had pectin based structure and the degree of esterification (DE) was calculated to be 38%. Based on 1D & 2D NMR spectroscopy, the major sugar residue of GSP molecule was 4-α-D-GalpA, other residues including 2-α-L-Rhap, 2,4-α-L-Rhap, α-L-Araf, β-D-Galp, 4-β-D-Galp were also evidenced in GSP. As a pectin molecule, GSP contained mainly homogalacturonans structure, while a small portion of rhamnogalacturonan I character was also identified.