Isolation, PuriHcation And Structural Analysis Of Starch-like Polysaccharides From Dioscorea Bulbifera L.

Rhizoma Dioscoreae bulbiferae is dried tuber of Dioscorea bulbifera L. It hasbeen reported that Rhizoma Dioscoreae bulbiferae contains many active componentsincluding terpenoids, saponins, flavonoids and polysaccharides. The activities ofantitumor and treatment of thyroid diseases have been researched and applicated inclinically. Polysaccharides play an essential role on the activity of RhizomaDioscoreae bulbiferae, but there is little study on it. In this paper, we made the studieson purification and structural analysis of the starch-like polysaccharides in order tofurther understand the structure and composition of Rhizoma Dioscoreae bulbiferaepolysaccharides.The water-soluble total polysaccharides of dry pieces of Rhizoma Dioscoreaebulbiferae (DBP) was extracted with hot water, precipitated by80%ethanol. Themonosaccharide of composition of DBP is1.4%Man,1.0%Rha,1.6%GalA,18.0%GlcA,44.4%Glc,32.9%Gal and0.7%Ara.DBP was divided into DBPN and DBPA by DEAE-Cellulose column.Monosaccharide composition analysis indicated that DBPN was mainly composed ofGlc (56.2%) and Gal (41.5%). The molecular weight distribution of DBP was wideand heterogeneous. DBPN was divided into good solubility fraction(DBPNS) andpoor solubility fraction(DBPNI) according to the different solubility in water.DBPNI was mainly composed of Glc (97%) and a small amount of Gal (3%).DBPNI does not dissolve in cold water, but it can completely dissolve in hot water,and it can make the potassium iodide reagent turns blue.13C NMR and methylationanalysis indicated that DBPNI was a starch-like glucan with the glycosidic link ofα-(1â†'4) with branch of α-(1â†'6), which degree of branch was5%.DBPNS was fractionated by freeze-thawing process to give two fractions,DBPNS-P (precipitate,10.7%) and DBPNS-S (supernatant,77%). DBPNS-Pcontained93%of glucose and7%of Gal. DBPNS-S has high solubility, and it wasmainly composed of Glc (37.5%) and Gal (57.4%).DBPNS-S was hydrolyzed by endo-β-(1,4)-galactanase to remove the galactan，then the hydrolysate was separated by size-exclusion chromatography to get twofractions, DBPNS-S-UD (10.1%) and DBPNS-S-D (55.0%). DBPNS-S-UD wasmainly composed of Glc (95.2%) and a trace amount of Gal (3.2%) and Man (1.6%),its molecular weight was about3,500Da.13C NMR and methylation analysis indicated that DBPNI was a starch-like glucan with the glycosidic link of α-(1â†'4)with branch of α-(1â†'6), which degree of branch was8.3%.