Structure And Antioxidant Activity Study Of Polysaccharides By Ultrasound Assited Extraction From Okra Flowers

The okra plant,Abelmoschus esculentus(L.)Moench,is a native plant from Africa.Okra flower is rich in carbohydrates protein,amino acids,unsaturated fatty acids and potassium,deserving further investigation due to its high nutrition.Various functions and physicochemical properties have been reported for polysaccharides from okra pods.It is suggested that okra polysaccharides can be used as diverse food ingredients.However,there are few reports on okra flower which is good resource of polysaccharides too.In this study,we optimized the ultrasound-assisted extraction condition of polysaccharides.The purification,chain conformation in aqueous solution and structural features of the polysaccharide were also investigated.1.The impacts of four extraction methods(hot water,acid,enzyme assistance,ultrasonic assistance)on the extraction yields,preliminary structure and antioxidant activities of the okra flower polysaccharides were systematically investigated.Four kinds of polysaccharides had the same monosaccharide composition,but mere difference in the content;they all had typical FT-IR spectra characteristic of polysaccharides.Their obvious difference was in yield,molecular weight distributions and intrinsic viscosity,as well as different surface morphology.Through the measurements of antioxidant activities in vitro,UOFP exhibited the most significant scavenging capacities and antioxidant activities.These data showed that ultrasonic assistance was more beneficial to obtain higher bioactive polysaccharides.2.Response surface methodology was employed to optimize the ultrasound-assisted extraction process of polysaccharide from okra flowers.On the basis of single factor experiment,the optimal conditions were obtained at the extraction temperature of 55 ℃,extraction time for 30min,ultrasonic power of 85.5 W and raw material to water at the ratio of 1:40.Under such conditions,the experimental yield of polysaccharide was 12.62%,which well matched with the value predicted by the model.3.A homogenous polysaccharide,named as UOFP-2,was obtained by ultrasonic assistance extraction and purified by DEAE-Q Sepharose Fast Flow column chromatography.Periodic acid oxidation and Smith degradation,HPLC,FT-IR,1D and 2D NMR spectroscopy analysis of the UOFP-2 revealed a backbone repeating units of→2)-α-Rha-(1-4)-a-GalA-(1→dimers and homorhamnan,side chains may consist of galactosyl groups.The weight average(Mw)molecular weight and intrinsic viscosity of UOFP-2 were 217 kDa and 1.78 dL/g,respectively.Intrinsic viscosity is related to molecular weight as the Mark-Houwink-Sakurada equation([η]-KMα).The a value(a=0.31)near to 0.33 indicated also a spherical conformation in water,confirmed by AFM.4.Furthermore,in vitro tests on antioxidant activity revealed that UOFP-2 exhibited significant antioxidant activity in a dose-dependent manner.The oxygen radical absorbance capacity(ORAC)and CAA value of UOFP-2 were 30.38 μmol Trolox/g and 342.98 μmol QE/100g,respectively.IC50 value was 5.89 mg/mL against hydroxyl radicals.