Total fractionation and characterization of the water-soluble polysaccharides isolated from Panax ginseng C. A. Meyer

Abstract

Water-soluble polysaccharides isolated from the roots of Panax ginseng C. A. Meyer were completely fractionated into two neutral fractions (WGPN and WGPA-N) and six acidic fractions (WGPA-1-RG, WGPA-2-RG, WGPA-1-HG, WGPA-2-HG, WGPA-3-HG and WGPA-4-HG) by a combination of ethanol precipitation, ion-exchange and gel permeation chromatographies. The analytical results showed that WGPN was a starch-like glucan; WGPA-N was a mixture of starch-like glucan and arabinogalactan; WGPA-1-RG and WGPA-2-RG were composed of major neutral sugars and minor acidic sugars that belong to the type-I rhamnogalacturonan (RG-I)-rich pectins, while fractions WGPA-1-HG to WGPA-4-HG were mainly composed of galacturonic acid (GalA, 62.4–92.1%) and have been identified to be homogalacturonan (HG)-rich pectins with different degrees of methyl-esterification, ranging from 0% to 30%. High performance gel permeation chromatography (HPGPC) showed that the six acidic fractions were homogenous, with molecular weights approximately ranging from 3.5 × 10³ to 1.1 × 10⁵. Lymphocyte proliferation assays showed that both the neutral polysaccharides and acidic polysaccharides were potent B and T cell stimulators.

Introduction

Panax ginseng C. A. Meyer (P. ginseng) has been used in China as a traditional medicine for over 2000 years. It is believed to be a panacea and to promote longevity. P. ginseng contains many active components, including ginsenosides, ginseng peptides and ginseng polysaccharides. It has been reported that P. ginseng polysaccharides have immunomodulation, anti-tumor, anti-adhesive, anti-oxidant and hypoglycemic activities (Song et al., 2002, Lee et al., 2006, Fu et al., 1994, Shin et al., 2004, Luo and Fang, 2008, Suzuki and Hikino, 1989).

Since the first report from Ovodov and Solov’eva (1966), many studies have been conducted on P. ginseng polysaccharides regarding purification, structural analysis and bioactivities. It has been reported that P. ginseng polysaccharides contain starch-like polysaccharide and pectin (Ovodov & Solov’eva, 1966). The ginseng starch-like polysaccharide consists of 3-branched α-d-(1,6)-glucans (Luo and Fang, 2008, Tomoda et al., 1984, Oshima et al., 1985, Tomoda et al., 1985) and 6-branched α-d-(1,4)-glucans (Fu et al., 1994). The ginseng pectin mainly consists of galactouronic acid (GalA), galactose (Gal) and arabinose (Ara). In addition, it also contains minor amounts of glucose (Glc), rhamnose (Rha), mannose (Man) and glucouronic acid (GlcA). Structural analyses have revealed that P. ginseng pectin contains α-(1,4)-linked galacturonopyranosyl residues, β-(1,3)-, β-(1,4)- and β-(1,6)-linked galactopyranosyl residues and α-(1,3)- and (1,5)-linked arabinofuranosyl residues (Solov’eva et al., 1969, Tomoda et al., 1994, Tomoda et al., 1993a, Tomoda et al., 1993b).

The Changbai Mountain region of China is one of the main regions for commercial P. ginseng harvesting. The relatively large supply of ginseng makes it possible to produce P. ginseng on an industrial scale. During ginseng processing, the valuable water-soluble polysaccharides are usually discarded, despite the fact that they may be widely used in the food industry and medicine. Use of these polysaccharides is restricted for various reasons, where one of the main reasons is that studies on ginseng polysaccharides are not sufficient to support the applications. Although there have been quite a few studies on P. ginseng polysaccharides, there is a lack of understanding of all of the ginseng polysaccharides. Up until now, it has been unclear how many polysaccharide fractions are present in the water-soluble ginseng polysaccharides and what their structure-activity relationships are. Thus, there is a real need to develop a practical procedure based on which ginseng polysaccharides could be completely fractionated into well-defined polysaccharide fractions in sufficient amounts to obtain further insights into their biological activities.

To exploit ginseng polysaccharides for food and medicinal applications, we recently designed a research program to completely fractionate P. ginseng polysaccharides and then systematically study the bioactivities of each fraction. We now report the first part of the results of the research program, the total fractionation of the water-soluble ginseng polysaccharides by a combination of anion-exchange and gel permeation chromatographies. Furthermore, we also show the macromolecular features and initial immunological activities of these fractions.