Study On The Chemical Modification,Antioxidant Activity In Vitro And Prebiotic Activity Of Rapeseed Polysaccharides

In the present study,the polysaccharide（RPM1-a）from rapeseed was prepared through extraction and purification.The primary structure of RPM1-a was characterized by methylation analysis and nuclear magnetic resonance（NMR）,while its rheological properties were evaluated.Moreover,the sulfation,acetylation and carboxymethylation derivants of RPM1-a were prepared,and their antioxidant activities and effects on probiotics in vitro were also tested.The main contents and results are as follows:1.Extraction and purification of rapeseed polysaccharides.Crude polysaccharides were obtained after extraction with NaOH aqueous solution and operation of deproteinization,decolouration,precipitation,and lyophilization.The crude polysaccharides were loaded on DEAE Bestarose column.Deioned water and 0.10 mol/L NaCl solution were used as eluents in turn.The fraction eluted by deioned water was gathered and then futher purified by Chromdex 200.Finally one main fraction named as RPM1-a was obtained.2.The primary structures of RPM1-a was studied.FT-IR spectrum of RPM1-a indicated that it was a kind of polysaccharide.HPLC analysis showed that RPM1-a was homogeneous with the molecular weight of 15.96 kDa.The gas chromatography analysis showed that RPM1-a was composed of rhamose,arabinose,glucose and galactose as the molar ratios of 3.70: 47.00: 21.30: 27.90%.The backbone of RPM1-a was made up of 6)-β-Galp-（1→,→3,4）-α-Rhap-（1→ and →4）-α-Glcp-(1→.Among them,O-3 and O-4 position substituted by branched chain.The main branched chain was consisted of β-Araf-（1→（5-β-Araf-1）16→（3-β-Araf-1）13→3）-β-Galp-(1→,and the secondary branched chain was consisted of β-Galp-（1→4）-β-Galp-(1→.3.The rheological properties of RPM1-a was also studied.The viscosity of RPM1-a was significantly affected by its concentration.The solution viscosity was relatively lower at lower concentrations,which was approximately Newtonian fluid.Meanwhile,the solution was approximately pseudoplastic fluid at a higher concentration.Similar to other fluids,when the temperature rose,the viscosity of RPM1-a was subsequently reduced.The pH impacted the viscosity of RPM1 significantly.As the pH rose from 5 to 9,the viscosity of RPM1 solutions was increased accordingly.As the pH was higher than 9,the viscosity was decreased.Ca²⁺ also affected the viscosity of RPM1 significantly,and with the concentration increasing,the solution viscosity rose.4.Chemical modification of RPM1-a.After sulfation,acetylation and carboxymethylation of RPM1-a,the chemical modification derivants were named SRPM1-a、AcRPM1-a and CRPM1-a,respectively.Characteristic absorption peaks of S=O,C-O-S and O-S-O appeared at 1250 cm-1,830 cm-1 and 588cm-1,new characteristic absorption peaks of H-C=O and C-O at 1373 cm-1,1247 cm-1,new characteristic absorption peaks of C=O,C-O and COO-at 1596,1421 and 1324 cm-1 in the FT-IR spectrum of SRPM1-a,AcRPM1-a and CRPM1-a indicated that sulfation,acetylation and carboxymethylation modifications were successful.5.The antioxidant activities of RPM1-a,SRPM1-a,AcRPM1-a and CRPM1-a were studied.The results showed that the anti-oxidative activity of RPM1-a was improved after modifications and the total reducing power and superoxide anion scavenging capacity of SRPM1-a better than the others.6.The proliferative effect of RPM1-a and its chemical modification derivatives on probiotics was studied.The proliferative experiments of four selected probiotics（Lactobacillus acidophilus,Bifidobacterium infantis,Bifidobacterium adolescentis,and Bifidobacterium bifidum）were carried out in vitro,and the effects were estimated according to the changes of OD and pH value of the cultivated media.The results showed that RPM1-a,SRPM1-a,AcRPM1-a and CRPM1-a could stimulate the proliferation of the probiotics significantly.Among them,SRPM1-a exhibited better proliferation effect than the others.The appropriate concentration of RPM1-a,SRPM1-a,AcRPM1-a and CRPM1-a for probiotics was 1.5%².0%.Furthermore,the pH values of the media decreased during the cultivation,which indicated that the RPM1-a and its derivants（SRPM1-a,AcRPM1-a and CRPM1-a）could be utilized by probiotics and translated into SCFA.The results of growth rate test showed that the probiotics could reach plateau phase after cultivated for 32 h when supplemented with RPM1-a.However,the plateau phase was reduced to 24 h when supplemented with SRPM1-a and AcRPM1-a,indicating that the enzymatic derivatives had better proliferative effect on probiotics than rapeseed polysaccharides.