Structure Characterization,physicochemical Properties And Antioxidant Activities Of Polysaccharide From The Fruit Of Opuntia Dillenii Haw

In this paper,wild cactus fruit(Opuntia dillenii Haw.)purchased from Sanya,Hainan province,was used as raw material,and the structure,physical and solution conformation properties and antioxidant activity of cactus fruit polysaccharides were investigated.An acidic polysaccharide fraction named as OFPP(O.dillenii Haw.fruit pectic polysaccharide,OFPP)was isolated and purified from O.dillenii haw fruits by hot water extraction,alcohol precipitation,decoloration,deproteinization,DEAE cellulose 52 and Sephacryl S-400 column chromatography.The physicochemical properties of OFPP were investigated by HPGPC,UV,SEM,Raman,XRD,Zetasizer,and TG-DSC.The results revealed that OFPP was a homogeneous heteropolysaccharide with an average molecular weight of 1.98×103 KDa.Uronic acid content of OFPP was 34.29%,and it contained neither protein nor nucleic acids.The zeta potential of OFPP was-24 mV,and it presented non-Newtonian fluids and belonged to pseudoplastic fluids.Moreover,the results indicated the OFPP exhibited good thermal stability and loose flaky morphology with semi-crystalline structure.In addition,the primary structure and solution conformation characterization of OFPP were investigated by GC,GC-MS,FT-IR,NMR,Helix-coil transition assay,Circular dichroism spectroscopy,TEM and AFM.The results revealed that OFPP consisted of rhamnose(40.8%),galactose(34.5%),arabinose(14.4%),glucose(5.9%),fucose(1.8%),xylose(1.6%),and mannose(1%).OFPP may be a kind of pectic polysaccharide.The OFPP was composed of repeating disaccharidic fragments units of →2)-α-L-Rhap-(1→4)-α-D-GalpA-(1→ as the backbone and partly substitution by neutral sugars including α-L-Araf,α-D-Galp and α-D-Glcp(mainly at O-4 position of certain α-L-Rhap)as side chains.Moreover,OFPP lacked triple-helix conformation and exhibited sphere-like conformation in the solution.In addition,the AFM images further confirmed that OFPP exhibited a spherical conformation in aqueous solution with the molecular diameter of 26 nm and the height of 5.9 nm.Furthermore,antioxidant activities of OFPP were investigated using various in vitro assay systems.The results indicated that OFPP exhibited scavenging activity of hydroxyl radical,chelating activity of ferrous ion and reducing power in a dose-dependent manner,but in vitro antioxidant activities were relatively weak.