The Structural Characteristics Of Purple Sweet Potato Polysaccharide And Its Preventive Effect On Non-alcoholic Fatty Liver

Purple sweet potato is the characteristic variety of sweet potato,which has high edible and medicinal value.In recent years,domestic and foreign scholars mainly isolated and identified anthocyanins,flavonoids,total phenols and small molecular weight polysaccharides and other active substances in purple sweet potato.Studies on their activities also mainly focus on antioxidant and immunity enhancement.However,there are few reports on the isolation,purification,structure analysis,liver protection and the mechanism of high molecular weight polysaccharide of purple sweet potato.In this paper,the extraction,isolation and purification,the structural characteristics of polysaccharides from purple sweet potato,as well as its liver protective effect on non-alcoholic fatty liver disease(NAFLD)mice induced by high fat diet were studied.The research results are shown follows:Firstly,the extraction process of polysaccharides from purple sweet potato was further optimized through a one factor test and response test.The results show that extraction time is 2.5 h,extraction temperature 80℃,solid-liquid ratio 1:15,and the extraction yield was8.85%.The crude purple sweet potato polysaccharide(CPSPP)was obtained after deproteinization,decolorization and dialysis.CPSPP was purified by Sepharose 4B to obtain a single polysaccharide component PSPP-A with a molecular weight of 2.63×10~3KDa.The total sugar content,protein content and uronic acid content of PSPP-A were96.2%,0.8%and 23.47%respectively.The primary structure of PSPP-A was analyzed by FT-IR,monosaccharide composition,GC-MS,and NMR.The results showed that PSPP-A hadαandβglycoside bonds,and it was composed of Rha,Ara,Gal,Glc and Glc A and with the molar ratio of 1.89:8.45:1.95:1.13:1.The sugar residue were 1,3-α-L-Araf,T-α-L-Araf,1,2,4-α-L-Rhap,4-O-Me-β-D-Glc Ap,1,4-α-D-Glcp,4-β-D-Galp and1,6-β-D-Galp,and the structural formula of PSPP-A was speculated.Congo red experiment showed that PSPP-A has three helix conformation,scanning electron microscopy(SEM)and atomic force microscopy(AFM)observed that PSPP-A showed lamellar morphology and chain structure.In order to investigate the protective effect of PSPP-A on mice liver,a model of non-alcoholic fatty liver(NAFLD)was established by high-fat diet.The results showed that PSPP-A could alleviate the abnormal increase of body weight,liver index,serum and liver TG,TC,AST and ALT levels induced by high fat diet(P<0.05)compared with the model group.The histopathological observations of livers indicated that PSPP-A could attenuate irregular hepatocyte arrangement with excessive lipid vacuoles and accelerate lipid breakdown in mice.Western blotting showed that PSPP-A could up-regulate the expression of hepatocytes FFAR3 receptors and AMPK,inhibit the expression of TRIB3 and ETV5,reduce abnormal accumulation of liver lipids and improve fatty liver injury.As a result,PSPP-A could prevent and improve dyslipidemia due to high fat diet,and to some extent alleviate non-alcoholic fatty liver in mice.The results of the study gave ideas for the development and use of purple sweet potato,and lay a theoretical foundation for further elucidating the liver protective effect and mechanism of purple sweet potato.