Study On The Extraction, Isolation, Structure And Antihyperglycemic Activity Of Polysaccharides From Mulberry Leaves

Mulberry leaf is a traditional Chinese herb.Mulberry leaves are widely planted in China,but most of them are discarded because it is mostly used to feed silkworm(Bombyx mori L.) in China.Polysaccharide is one of the major chemical components of mulberry leaf. Polysaccharides from plants have multiple bioactivities,such as antihyperglycemic activity,antineoplasmic activity and anti-oxidation activity.Therefore,it is meaningful to do research on polysaccharides from mulberry leaves.Mulberry leaves were obtained from a commercial orchard in Huzhou,Zhejiang Province,and then employed to extract polysaccharides.Extraction,isolation,structure identification and bioactivity of polysaccharides from mulberry leaves were further studied. The major results obtained in this study were as follows.Response surface method(RSM) was applied to optimize extractions of polysaccharides from mulberry leaves,including conventional solvent extraction(CSE),microwave-assisted extraction(MAE) and ultrasound-assisted extraction(UAE).The optimum conditions of CSE were obtained as follows:extraction temperature 80℃,the dry/water weight ratio 1:17,extraction time 85 min,and the yield of polysaccharides could be up to 4.67%with two-times extraction.The optimum conditions of MAE were obtained as follows:dry/water weight ratio 1:25,extraction time 11min,microwave power was 436W,and the yield of polysaccharides was 9.53%.The optimum extraction conditions of UAE were obtained as follows:extraction temperature 80℃,dry/water weight ratio 1:15,power of ultrasound 60W,extraction time 20min,and the yield of polysaccharides was 10.88%.Compared with CSE,the yield of polysacchrides increased 104%and 131%for MAE and UAE,respectively.Therefore,MAE and UAE were good methods for extracting polysaccharides from mulberry leaves.Three different macroporous resins(AB-8,D101 and D3520) were used to decolor and deproteinize crude polysaccharides from mulberry leaves.Macroporous resins D3520 had the best effect.The obtained polysaccharides were further isolated with DEAE Sepharose Fast Flow ion exchange column and Sephadex G-100 column,and got two components(MPS-1 and MPS-2).They were pure determined by HP GPC and CAME.The structure of MPS-1 and MPS-2 was analyzed with chemical methods.From FT-IR,MPS-1 and MPS-2 were polysaccharides.MPS-1 had more functional groups than MPS-2.From HP GPC analysis, molecular weight of MPS-1 and MPS-2 were 24898 D and 61131D, respectively.From GC analysis,MPS-1 was composed of Sor,Ara,Xyl and Glc with molar ratio of 3:2:17:110.MPS-2 was composed of Rha, Ara,Xyl,Glc,Gal and Man with molar ratio of 13.8:9.7:14.4:9.6:9.3: 13.5.The hypoglycemic activity of polysaccharides from mulberry leaves in alloxan-induced mice was investigated.It was found that polysaccharides from mulberry leaves had hypoglycemic activity.It could improve the weight,lower blood sugar level,enhance antioxidant activities,promote the conversion of blood glucose into liver glycogen, and relieve the lesion of pancreas induced by alloxan.The hypoglycemic effect may be due to the improving activity of antioxidases in mice by eliminating oxygen free radical to promote the renovation of liver andβ-cell.Further studies are necessary to do on the mechanism and identification the component which plays the hypoglycemic effect.