Abstract: To provide the theoretical foundation for further development and utilization of Polygonatum cyrtonema Hua,the sequential extraction and structural composition of P.cyrtonema polysaccharides (PCP) were studied.After removal of resin under petroleum ether reflux,crude polysaccharides were extracted from P.cyrtonema by water and different concentrations of alkaline solution extraction,and alcohol precipitation.Five samples (PCP1,PCP2,PCP3,PCP4 and PCP5) were successfully obtained.Their chemical structures and physical properties were characterized by monosaccharide analysis,Fourier-transform infrared spectroscopy (FT-IR), molecular weight determination,NMR spectroscopy and thermal analysis.Monosaccharide analysis indicated that the five polysaccharides basically all contained arabinose,galactose,glucose,mannose,xylose,glucuronic acid and galacturonic acid,but the relative amount of each monosaccharide were different.The FT-IR spectra revealed that the structure of PCP had the typical characteristics of carbohydrate polymer with pyranoid rings.The average molecular weights (Mw) of the five polysaccharides were 2090 Da,38600 Da,42600 Da,34300 Da and 24100 Da,respectively.Six types of residues of PCP1 were connected by β and α-glucoside bond.But residues of PCP3 and PCP5 were only connected by α-glucoside bond.Compared with water extraction sample,further alkaline solution extraction samples had higher dispersion degree,non-uniform molecular chain distribution and less thermal stability.In addition,it was found that when the concentration of alkaline was higher,the thermal stability was worse. ¹³C-NMR spectra showed PCP1 anomeric carbon configuration was mainly β- type with a small amount of α-type,contained six sugar residues.PCP3 and PCP5 anomeric carbon configurations were α type.PCP3 contained four sugar residues and PCP5 contained two sugar residues.

Key words: Polygonatum cyrtonema Hua, polysaccharides, monosaccharide composition, thermal stability, structural analysis