Structure Characterization,Dipeptide Modification And Bioactivities Of Polysaccharides From Lachnum YM40

In this study,two novel polysaccharide fractions(LEP-1a,LEP-2a)were obtained through fermentation,extraction and purification from Lachnum YM40.The structural characteristics,physicochemical properties,antioxidant and hypolipidemic activities of polysaccharide fractions were investigated and compared.The digestion characteristics of LEP-2a were explored by using in vitro simulated digestion model.LEP-2a-dipeptide derivative(LAG)was prepared,and the protective effects of LEP-2a and LAG on the gastric mucosa of mice with ethanol-induced gastric ulcer were studied.The main results are as follows:Crude polysaccharides were extracted and separated from the fermentation broth of Lachnum YM40,and then purified by DEAE Cellulose-52 and Sephadex G-100chromatography to obtain water-washed polysaccharides(LEP-1a)and salt-washed polysaccharides(LEP-2a).HPGPC,GC-MS,FT-IR,methylation and NMR analysis showed that LEP-1a was a heteroglycan with a molecular weight of 22.50 k Da,which was composed of mannose,galactose and glucose with the molar ratio of48.98:43.59:7.43.The glycosidic linkages of LEP-1a were composed of(1→2)-β-D-Galp,(1→2,6)-ɑ-D-Manp,1→)-ɑ-D-Manp,(1→4)-β-D-Galp,(1→6)-ɑ-D-Manp,(1→2)-ɑ-D-Glcp,(1→4)-β-D-Glcp,(1→2)-ɑ-D-Manp,and(1→3,6)-β-D-Manp.While LEP-2a was composed of mannose,galactose,glucose and galacturonic acid in the molar ratio of66.91:30.75:1.6:0.74,with a molecular weight of 47.02 k Da,and a small amount of uronic acid was detected.The glycosidic linkages of LEP-2a mainly contained 1→)-ɑ-D-Manp,(1→2)-β-D-Galp,(1→2,6)-ɑ-D-Manp,(1→6)-ɑ-D-Manp,(1→2)-ɑ-D-Glcp.SEM,AFM,and rheological properties analysis showed that compared with LEP-1a,LEP-2a presented a denser porous dendritic winding structure and higher viscosity.Moreover,LEP-2a exhibited stronger free radicals scavenging activities,reducing power,bile acid-binding and cholesterol-binding capacity,and inhibitory activity on lipase.The changes of components and biological activities of LEP-2a during the in vitro digestion of saliva,simulated gastric and intestinal were investigated.The results showed that LEP-2a could not be digested by saliva.While the molecular weight decreased and the reducing sugar content increased after in vitro simulated gastric and intestinal digestion.Atomic force microscopy showed that the height and branching degree of LEP-2a decreased significantly after gastrointestinal digestion.The evaluation of antioxidant activities showed that LEP-2a had better scavenging activity against DPPH,ABTS~+free radicals and reducing power in the gastrointestinal digestive environment,and the activities increased with the extension of digestion time,but was less affected by saliva.Besides,the addition of polysaccharides in lipid emulsion could inhibit the decomposition of lipids during gastrointestinal digestion.LEP-2a was modified with Alanyl-Glutamine(Ala-Gln)and an ethanol-induced acute gastric ulcer model was constructed to investigate the protective effects of LEP-2a and its derivatives(LAG)on gastric mucosa in mice.The results showed that high-dose of LAG and LEP-2a could significantly inhibit the pathological damage of gastric mucosa,increased the activities of SOD and GSH-Px,and reduced the levels of MDA,MPO and pro-inflammatory factors level(TNF-α,IL-1βand IL-6)of gastric tissue.Western blot analysis showed that LAG and LEP-2a could inhibit the protein expression of p-JNK,p-ERK,p-IκBαand p-NF-κBp65.In addition,LAG could up-regulate the defense factor PGE2 and promote the formation of the mucus barrier.These results indicated that LAG and LEP-2a could protect the gastric mucosa of mice with gastric ulcer by reducing oxidative stress and blocking MAPK/NF-κB pathway.The protective effect of LAG on gastric mucosa was better than that of LEP-2a.