Studies On Extraction,isolation,Purification And In Vitro Bioactivity Of Water-soluble Polysaccharides From Dendrobium Nobile Lindl. Leaves

In order to promote the full utilization of Dendrobium nobile Lindl.The investigation of Dendrobium nobile Lindl.leaves was carried out on drying technology,extraction,purification,in vitro biological activities of water-soluble polysaccharides of Dendrobium nobile Lindl leaves.In the meantime,the final purified polysaccharide(DNLP-W1)was obtained;the physicochemical properties and in vitro biological activity.of DNLP-W1 were studied was analyzed as well.The main contents and results are as follows:(1)The main components of Dendrobium nobile Lindl.leaves were analyzed including water,total sugar,crude protein,crude fat,ash,flavonoids and dendrobium.Their contents were,85.37%,12.09%,9.56%,7.89%,3.74%,1.35%,and 0.15%,respectively.(2)The effects of microwave,hot air,vacuum and freeze drying on the polysaccharide content of Dendrobium nobile Lindl.leaves were compared.The results showed that the content(dry base)of total polysaccharide in Dendrobium nobile Lindl.leaves was 3.11%,3.02%,2.81% and 2.74%,respectively,by vacuum freeze drying,vacuum drying,hot air drying and microwave drying.(3)The extraction of polysaccharides from Dendrobium nobile Lindl.Leaves was optimized by response surface method.The resultant optimal extraction condition was temperature of 82℃,the ratio of material to liquid of 1:30(g/mL)and the extraction time of 3.3h,yield was 10.27% and the polysaccharide content was 38.64%.(4)The optimal condition of decolorization was as follows,the ratio of resin(D301)to extract was 0.33 g/mL,the decolorization time was 3.4 h and the decolorization temperature was 47 ℃.Under above conditions,the decolorization rate of polysaccharides of Dendrobium nobile Lindl.leaves was 92.34 %,retention rate of polysaccharide and the polysaccharide content were 74.67% and 51.32%.(5)The decolorized polysaccharides was deproteinized by Sevag method,and purified by Cellulose DE-52 and Sephadex G-100 column.As a result,one homogeneous polysaccharide DNLP-W1 was obtained,its yield was 2.04% and the polysaccharide content was 93.74% with a relative molecular weight of 4.17×104 Da.Monosaccharidic constitutent present in DNLP-W1 included arabinose,galactose,glucose and xylose with the molar ratio of 1.00:1.33:1.27:14.05.Thermal analysis showed that DNLP-W1 had a characteristic decomposition temperature of 256.6℃ and good thermal stability.(6)The in vitro bioactivity of crude polysaccharides and its purified fraction DNLP-W1 of Dendrobium nobile Lindl.leaves was evaluated by the inhibitory activities of α-glucosidase,α-amylase and the scavenging ability of DPPH,ABTS+ free radicals.The results show that the inhibition rates of crude polysaccharides and DNLP-W1 to α-glucosidase and α-amylase were 45.63%,39.91% and 36.74%,31.06%,respectively,when the concentration of polysaccharide was 10 mg/m L.The scavenging rates of crude polysaccharides and DNLP-W1 to DPPH and ABTS+ free radicals were 68.24%,74.01 %and 56.74%,40.22%,respectively,when the concentration of polysaccharide was 2.5 mg/mL.