Structural Characterization,Physicochemical Properties And Hypoglycemic Activity Of Polysaccharides From The Fruits Of Wax Apple

In the present study,wax apple(Syzygium samarangense Merr.& Perry)fruits produced from Sanya,Hainan province,were used as raw material,and the structure,physicochemical properties and hypoglycemic activity of wax apple fruits were investigated.Wax apple fruits were washed,peeled,mashed and homogenized.After hot water extraction,precipitation with alcohol at a concentration of 40%(v/v)and deproteinization,crude polysaccharides were isolated from the fruits of wax apple.After further purification of the crude polysaccharides by DEAE-52 cellulose ion-exchange chromatography and Sephacryl S-300 size-exclusion chromatography,a water-soluble polysaccharide fraction(WAFP)was obtained.The WAFP was identified as a homogeneous polysaccharide fraction with molecular weight of 49.9 k Da by high performance gel permeation chromatography(HPGPC).The content of total sugar in WAFP was 89.22% and uronic acid content was 31.38%.WAFP was mainly composed of rhamnose,arabinose,xylose,mannose,glucose,and galactose with a molar ratio of 1.88: 2.20: 6.37: 1.48: 5.47: 2.82.Combined with Fourier transform infrared spectroscopy(FT-IR),methylation and NMR analysis results,WAFP consisted of ?2)-?-L-Rhap-(1? and ?4)-?-D-Galp A-(1? as the backbone and ?4)-?-D-Glcp-(1? ? ?3,5)-?-D-Araf-(1? ? ?3)-?-D-Manp-(1? and ?3,4)-?-D-Xylp-(1? as side chains.The atomic force microscope(AFM)images showed that the height of the WAFP was about 12.8 nm and the polysaccharide chain presented the size of a uniform rule of flame-like aggregates and multiple strands arranged closely.The congo red test indicated that no triple-helix structure was occurred in the WAFP solution.The physicochemical properties of WAFP were studied in the present study.The general physicochemical properties of WAFP were analyzed firstly,and then other properties were also studied.Viscosity property measurement showed that WAFP solution presented typical non-Newtonian fluids.The zeta potential of WAFP was-19.4 m V,which indicated that the polysaccharide fraction exhibited a relatively unstable state in the solution.Thermal characteristic results suggested that the WAFP exhibited good thermal stability.Moreover,scanning electron micrograph(SEM)results showed that the WAFP presented loose and incompact structure and exhibited rough surface with many small irregular particles which existed in the state of aggregation.In the present study,the possible protective effect of wax apple fruit polysaccharide against oxidative damage in streptozotocin(STZ)-induced diabetic mice were also investigated.During the experiment,the diabetic mice were administered WAFP at three levels of 50 mg/kg,100 mg/kg and 200 mg/kg via oral gavage every day.In the positive control group,the diabetic mice were administered metformin hydrochloride of 100 mg/kg.The experimental period was 4 weeks.The body weight,organ index,fasting blood glucose level,oral glucose tolerance and superoxide dismutase(SOD),catalase(CAT)and glutathione peroxidase(GPx)activities and malondialdehyde(MDA)level in serum,liver and kidney of diabetic mice were determined.The results indicated that oral administration of WAFP significantly increased the body weight and reduced fasting blood glucose levels of diabetic mice,while improved oral glucose tolerance of diabetic mice.Wax apple fruit polysaccharides also significantly increased the activities of antioxidant enzymes SOD,CAT and GPx,and reduced the level of MDA in serum,liver and kidney in STZ-induced diabetic mice.These results indicated that the WAFP exhibited significant hypoglycemic effect.