Structural characterization and immunological activities of the water-soluble oligosaccharides isolated from the Panax ginseng roots

Water-soluble ginseng oligosaccharides (designated as WGOS) with a degree of polymerization ranging from 2 to 10 were obtained from warm-water extract of Panax ginseng roots, and fractionated into five purified fractions (i.e., WGOS-0, WGOS-1, WGOS-2, WGOS-3, and WGOS-4) by gel-filtration chromatography. In order to ascertain the monosaccharide residues in the WGOS, a technique that combines acid hydrolysis and high-performance liquid chromatography was employed. It was found that only glucose residues were present in the WGOS. Fourier transform infrared spectroscopy and electrospray ionization tandem mass spectrometry provided the sequence, linkage, and configuration information. It is noteworthy that alpha-Glcp-(1 -> 6)-alpha-Glcp, alpha-Glcp-(1 -> 6)-alpha-Glcp-(1 -> 4)-alpha-Glcp, alpha-Glcp-(1 -> 6)-alpha-Glcp-(1 -> 6)-alpha-Glcp-(1 -> 4)-alpha-Glcp, and other six malto-oligosaccharides (i.e., maltopentaose, maltohexaose, maltoheptaose, maltooctaose, maltononaose, and maltodecaose) were detected in ginseng. Preliminary immunological tests in vitro indicated that WGOS were potent B and T-cell stimulators and WGOS-1 has the highest immunostimulating effect on lymphocyte proliferation among those purified fractions. It is hoped that the WGOS will be developed into functional food or medicine.