Isolation, Purification, Structural Analysis And Antioxidant Activity Of Polysaccharides From Dendrobium Officinale

Dendrobium officinale, is an entire grass with perennial epiphytic herb and belongs to Dendrobium Sw., orchidaceae. It mainly distributes in Guangxi, Anhui, Zhejiang, Yunnan, and other places. D. officinale is a precious traditional Chinese herbal medicine and has a distinguished effect of nourishing yin, clearing heat, benefiting the stomach, promoting saliva production, enhancing immunological competence, and delaying aging. Modern pharmacology research has shown that D. officinale have abundant dendrobium polysaccharides that are one of the main medicinal compositions and have strong biological activities.In this paper, polysaccharides from the stems of D. officinale were isolated and purified; then their structures were characterized and their antioxidant activities were evaluated in vitro. The results showed that the extraction rate of crude polysaccharides was 10.4% and sugar content was 60.88%. The crude polysaccharides were precipitated in water solution at different concentration ethanol to saperate into two farctions. Fraction CDOPB (85% ethanol precipitation) was isolated and purified by DEAE-cellulose and Sephadex G-100 gel filtration chromatography. Five new pure polysaccharides were obtained named DOPB1, DOPB2, DOPB3, DOPB4, and DOPB5, respectively.The structures of DOPB1, DOPB2, DOPB3, DOPB4 and DOPB5 were authenticated by GPC, UV, FT-IR, HPLC, GC-MS, NMR, periodate oxidation, and Smith degradation. The relative molecular weight of DOPB1, DOPB2, DOPB3, DOPB4, and DOPB5 were respectively estimated to be 8500,5302, 4699,5480, and 5408 Da. DOPB1 was composed of Man, Glc, Ara and Gal A in the molar ratio of 6.2:2.3:2.1:0.1. The structural analysis showed that DOPB1 was comprised of 2-Oacetylglucomannan residues, (1â†'4)-linked-β-D-Manp residues and (1â†'4)-linked-β-D-Glcp residues. DOPB2 was composed of Man, GlcA and Glc with a molar ratio of 3.42:0.11:1.08, Man and Glc were found in DOPB3 with a molar ratio of 8.56:1.12. DOP B4 was composed of Man and Glc in the molar ratio of 4.91:1.09, and DOPB5 was composed of Man and Glc with a molar ratio of 3.61:1.01. Except for DOPB2 contains β-configuration and a-configuration pyran acid heterosaccharide, other four polysaccharides containing β-configuration mannopyranose heterosaccharide.DPPH radicals, hydroxyl radicals, and metal chelating activities were used to evaluate the antioxidant activities of crute polysaccharides, CDOPA and CDOPB in vitro. Both CDOPA and CDOPB has strong metal chelating activities (CDOPA> CDOPB), obvious scavenging activities of hydroxyl radicals (CDOPA< CDOPB), and good scavenging activiairs of DPPH radicals (CDOPA< CDOPB).