Fractionation and characterization of water-solubleolysaccharides from Codonopsis pilosula ( Franch.) Nannf.

Dangshen, dried roots of Codonopsis pilosula ( Franch.) Nannf., is an important traditional Chinese medicine. Hot-water extractable polysaccharides of dangsen have been associated with its attributes of immunomodulatory activities. The main goal of this research was focusing on profiling and characterizing water-soluble polysaccharides of dangsen. Solubility and charge selective precipitation were employed to separate different polysaccharide fractions. Fructo-oligosacchride and fructan (or known as Inulin) and pectic polysaccharides have been selected as major targets because they are play important roles as active components in many herbal medicines. The fructan analysis was focused on linkage determination and molecular weight distribution. The study of pectic polysaccharides was focused on structural characteristics of rhamnogalacturonan I. The content of fructo-oligosaccharide and furctan of dangshen was found to be 26.65% and the weight-average molecular weight was 6.42 kDa (DP = 40) with degree of polymerization in the range of DP = 7 ~ 112. The fructo-oligosaccharides and fructans were hot-water extractable at 80C. Increasing ethanol concentration and decreasing extracting temperature decreased the extraction ratio. Yield of crude polysaccharides from sliced and dried dangsen, a common consuming form, was 12.86% by weight. Quaternary ammonium salt effectively separated high anionic polysaccharides through selective precipitation. The yield of polysaccharide precipitate and supernatant was 2.58% and 10.28%, repectively. The major sugar composition of the polysaccharide precipitate was galactouronic acid (69.91% molar ratio) with relative small amount of galactose, arabinose and rhamnose. It is a homogalacuronan (HG or pectic acid) component of pectic polysaccharide with weight-average molecular weight of 240.46 kDa. The fructan, remaining in the supernatant of quaternary ammonium reacted solution, was found to be the most abundant component in the crude polysaccharides with the ratio of 56.81％ and the weight-average molecular weight was 3.04 kDa (DP= 19). According to its susceptibility to inulinase and fructanase, the backbone of the fructan was found to be (2,1)-β-linkage. Other components found in the supernatant were two arabinogalactan enriched fractions, one neutral (DEAE-FractionI) and one low anionic charged, which could be further separated by using DEAE-anion exchange chromatography. The neutral arabinogalactan fraction was composed of galactose (62.95%), arabinose and rhamnose with molecular-weight of 369.5 kDa. The low anionic charged polysaccharide fraction was compose of galacturonic acid、arabinose、rhamnose and galactose and could reacted with artificial β-D-glucosyl Yariv antigen to form pink color indicating that it was a rhamnogalacturonan I carrying type II arabinogalactan ramified branches which was an bioactive polysaccharide found in many medical herbs.