Study On The Extraction Of Polysaccharides From Corn Bran By Subcritical Water Method With Extrusion-expansion Pretreatment

Corn bran is an agro-industrial byproduct that results from the wet milling step in corn starch production,it is usually confined within the fields of animal feeding,anaerobic fermentation,and sometimes treated as a waste that causes disposal problems.Corn bran contains complex carbohydrate polymers,such as cellulose,hemicelluloses,so it has received attention as a potential commercial source of polysaccharides.It is important for development of functional food and medicine to research Corn Bran Polysaccharides.In this present study,The main objective was to investigate the effect of the extrusion-expansion pretreatment on the polysaccharide products.Thus,corn barn was firstly treated by twin-screw extrusion-expansion and then extracted by hot-compressed water in a confined environment under various conditions.After separation and purification,the chemical properties and antioxidant activities of the corn bran polysaccharides were comparatively investigated.Corn bran was pretreated by the twin-screw extrusion-expansion at 110°C and 180°C.In addition,the characteristics of the untreated and pretreated corn bran samples were analyzed via X-ray diffraction(XRD),thermogravimetric analysis(TG),scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FT-IR).The results showed that the extrusion-expansion pretreatment undoubtedly changed the surface structures of the corn bran samples,improved the accessibility to solvents,improved the thermal stability and caused degradation of hemicellulose and cellulose of non-crystalline zone.On the whole,the twin-screw extrusion-expansion pretreatment mainly changed the physical structure and thermochemical properties of corn bran.corn barn was extracted by subcritical water in a confined environment under various extraction temperature and time.The main polysaccharides products were also analyzed by sugar analysis and FT-IR.The results found that the polysaccharide yield of un-pretreated sample reached a maximum at 180? and 40 min,while the polysaccharide yield of pretreated sample reached a maximum at 170? and 20 min.The crude corn bran polysaccharides were composed of arabinose,galactose,glucose,xylose,mannose and uronic acid,the predominant sugar constituent was glucose,which contained 39.37 % ~57.67 %.Comparatively,aextrusion-expansion pretreatment was developed to enhance the polysaccharide yield and decrease the optimum temperature and time during the hydrothermal treatment of corn bran.And the variation of monosaccharide composition indicated the pretreatment and the higher treatment temperature favored the degradation of hemicelluloses.FT-IR results indicated the pretreatment had no substantial effect on the structure of the polysaccharide fractions.The crude corn bran polysaccharides were respectively deproteinized by Sevag method,decoloried by D101 macroporous resin and removed small molecular impurities by dialysis method,then crude polysaccharide solution became clear and transparent,the quality was improved.The two components were obtained by DEAE-52 cellulose column chromatography and Sephadex G-50 column chromatography from crude polysaccharises obtained from un-pretreated and pretreated sample,named CBP-1,CBP-2,110P-CBP-1,110P-CBP-2,180P-CBP-1,180P-CBP-2,respectively.Each component only showed a elution peak in the elution cruve of Sephadex G-50 column chromatography,indicating that they were a single component.The molecular weight and sugar analysis were determined by high performance liquid chromatography(HPLC)and high performance anion exchange chromatography(HPAEC).The results showed that the molecular weights of CBP-1,CBP-2,110P-CBP-1,110P-CBP-2,180P-CBP-1,180P-CBP-2 are 39305 Da,6653Da,27008 Da,6035Da,13240 Da,6058Da,respectively.CBP-1,110P-CBP-1 and 180P-CBP-1,contained only glucose,were homopolysaccharide and neutral polysaccharide.CBP-2,110P-CBP-2 and180P-CBP-2 were heteropolysaccharide and acidic polysaccharide,which contained8.62%~10.87% arabinose,14.17%~18.00% galactose,11.13%~16.58% glucose,42.46%~47.73% xylose and 12.41%~18.20% uronic acid.The above data showed that the molecular weight of neutral polysaccharides was decreased and the content of xylose and uronic acid in acidic polysaccharides was increased after the pretreatment,.FT-IR and TG showed that the pretreatment had no significant effect on the basic structure of the polysaccharide,but it will reduce the thermal stability of neutral polysaccharides and improve the thermal stability of acidic polysaccharides.NMR and other results showed that the neutral polysaccharide may be the dextran with ?-1,4 and ?-1,4 glycosidic linkage.Acidic polysaccharide may be a hyperbranched polysaccharide with ?-xylose residue as thebackbone.The corn bran polysaccharide had a certain scavenging effect on hydroxyl radical,DPPH radical and superoxide anion free radicals,and the removal rate increased with the increase of concentration.The maximum removal rates were 32.56±0.79%(110P-CBP,1mg/mL)?48.68±0.86%(180P-CBP,1mg/mL)and 16.63±0.47%(110P-CBP,1mg/mL)respectively.The antioxidation ability of crude polysaccharide from pretreated corn bran was increased,while the antioxidant capacity of purified polysaccharide was decreased.