Study On The Extraction, Purification And Structure Of Polysaccharide From Rice Bran

The microwave-assisted technology for extracting polysaccharide from defatted rice bran was studied. The main parameters, such as the ration of material to liquid, microwave power and microwave extraction time were studied by single-factor experiment. The optimum conditions of microwave-assisted extraction were obtained by orthogonal experiment. Results are as follows: extracted for 2 min, the ration of material to liquid is l:10, and microwave power is 400 W. The yield of polysaccharide extracted by traditional hot water technology is 2.02%. The yield of polysaccharide extracted by microwave technology is 2.76%. Compared with the traditional hot water technology, the yield and the purity of rice bran polysaccharide extracted by microwave-assisted technology has increased by 36.6% and 5.7%.Microwave-assisted technology has the advantage of improving the extraction rate, while it has no influence on the physical and chemical characters of rice bran polysaccharide. Sevag, Trichloroaceticacid and enzymatic hydrolysis were used to remove protein from rice bran. The result showed methods of enzymatic hydrolysis are better than others. The removal of protein is 51.24%, the yield loss of RBP is 9.39%.RBP was purified by anion-exchange chromatography. Stepwise elution was done with a discontinuous gradient of water, 0.3 and 0.5 M NaCl at pH 8.0 and the flow rate was 1.5 ml/min. Four fractions, RBPⅠ, RBPⅡ, RBPⅢand RBPⅣwere collected.The anti-oxidation of four fraction polysaccharide RBPⅠ, RBPⅡ, RBPⅢand RBPⅣwas studied for the first time. RBPⅠand RBPⅡhave better scavenging effects of free radical, especially RBPⅡ. The DPPH·scavenging rate of RBPⅡis 77.59%, the O2.- scavenging rate is 65.33% and the·OH scavenging rate is 75.12%.RBPⅡwith anti-oxidation activity was purified by gel chromatography after anion-exchange chromatography. Two fraction of polysaccharide RBPⅡ-a and RBPⅡ-b were obtained. The major fraction RBPⅡ-a was eluted as a single symmetrical narrow peak on high-performance liquid chromatography (HPLC) and the average molecular weight was 120,645 Da.The Fourier-transform infrared spectra (FT-IR) and 1H, 13C NMR spectroscopy analysis revealed that RBPⅡ-a had a backbone consisting ofβ-(1→3)-linked D-galacopyranosyl residues substituted at O-2 with glycosyl residues composed ofα-D-xylose-(1→4)-α-D-arabinose-(1→andα-D-glucose-(1→4)-α-D-arabinose-(1→linked residues.