Extraction, Purification, Structural Idenfication And Immunoregulating Activity Of Polysaccharides From Dendrobium Chrysotorum Lindl.

Dendrobium chrysotorum Lindl., which belongs to Dendrobium Sw ofOrchidaceae, is an edible medicinal plant which has the functions of nourishingbody, clearing within fire, moistening lung, maintaining stomach tonicity and so on.The polysaccharide is one of the main and important active substance. In this paper,firstly, the nutritional compositions of Dendrobium chrysotorum stems wereanalyzed; then, the removing protein methods of the water souble polysaccharidesfrom Dendrobium chrysotorum (DCP) was optimized; at last, the isolation,purification, structural identification and immunoregulating activity of DCP werestudied. The results can be lised as follows:(1) The results showed that the content of total carbohydrate, reducingpolysaccharides, crude fats, total proteins and ashes of D. chrysotorum were33.68,0.57,6.63,1.40and2.60g/100g dried weight, respectively.(2) The yields of water souble polysaccharides (DCP-W), alkali soublepolysaccharides (DCP-B) and acid souble polysaccharides (DCP-A) from the stemsof D. chrysotorum were5.28%,0.71%and0.29%, respectively. Theimmunoregulating activity of DCP-W was higher than that of DCP-B and DCP-A.(3) The deproteining method of papain associated with Sevag was found to bethe best one for protein romval among the tested four deproteining methodsincluding Sevag, TCA, Papain and papain associated with Sevag. The deproteiningrate of70.68%was obtained and the loss rate of polysaccharides was only6.28%when the method of papain associated with Sevag was used.(4) DCP-W was fractionated by ion-exchange chromatography ofDEAE-Cellulose and further purified by gel permeation chromatography ofSephadex G100and Sephacryl S400giving three homogeneous polysaccharides ofDCP-W1, DCP-W2and DCP-W3with the average molecular weights of0.92×10~4Da,1.83×10~6Da and1.96×10~6Da, respectively. The structures of DCP-W1,DCP-W2and DCP-W3were analyzed by perhydrolysis, methylation, HPGPC,FT-IR, GC, GC-MS, NMR and so on. DCP-W1was composed of Man and Glc inthe molar ratio of2.9:6.9. DCP-W2was composed of Ara, Man, Glc and Gal in themolar ratio of0.9:6.1:9.0:1.0. DCP-W3was composed of Rha, Ara, Xyl, Man,Glc and Gal in the molar ratio of3.4:17.9:5.1:12.2:24.6:36.8. The polysaccharide structures of DCP-W1, DCP-W2and DCP-W3were inferred by theabove analysis and were shown as follows.The repeating unit of DCP-W1was established:The repeating unit of DCP-W2was established:DCP-W3was pectin heteropolysaccharide which had a backbone of1,4-linkedGalAp and1,2-linked Rhap resides in the molar ratio of1:1, with occasionallybranches at O-4and O-3. The branches were mainly composed of galactose, glucose,mannose, xylose...