Study On The Extraction, Purification And Characterization Of Oat β-glucan

Oat β-glucan is a kind of non-starch polysaccharide which is usually concentrated in theinner aleurone cell walls and subaleurone endosperm cell walls covering the ranges of 3-7% on adry basis. During milling, fractions enriched in β-glucan are transferred into oat bran. Naked oat isthe speciality cereal in China. This paper studied on the extraction ,fractionation, purificationand physicochemical properties and diverse functional properties of β-glucan from naked oatbran. In addition, the intestinal flora and physiological response in intestinal tract were alsoinvestigated.The suitable extraction technique for water-solubleβ-glucan from ShanXi naked oat branwas obtained by comparing the traditional extracted methods(hot water extraction) andmicrowave assisted extraction(MAE), and the corresponding extraction parameters were alsooptimized. Under optimum conditions, the yield ,the rate of extraction and the purity of the crudeoat β-glucan were compared of the two methods. All these results showed the method of MAEwas a effective method of extracting oat branβ-glucan. This method could save time and improveyield , the rate of extraction as well as purity.Composition analysis showed that the crudeβ-glucan extraction contained other impurities(protein , arabinose etc.). It was purified by adding (NH4)2SO4 and using DEAE Sepharose CL-6Bion-exchange as well as Sepharose CL-4B gel-filtration column chromatography. The purity ofPOG-1A was 98.6% by HPLC and fluorescence detection after consecutive ion-exchangechromatography and gel-filtration chromatography. Sugar component was mainly composed ofglucose by gas chromatography (GC). POG-1A molecular weight was 2.62×106 by HPLCanalysis.We used the method of Sepharose CL-4B gel-filtration column chromatography determiningthe relative molecular weight(Mr) distribution of the naked oat bran β-glucan extraction indifferent extracting conditions and analyzed the reasons. The results showed extraction conditionscould affect of the relative molecular weight of the extracted β-glucans. The distribution of Mr ofβ-glucans was 3.4×105-2.6×106 in the extracting conditions.A series of modern analysis methods, such as UV, IR, NMR and AFM(atomic forcemicroscope) as well as specific (1→3)(1→4)-β-D-glucan-4-glucanohydrolase combining withHPLC were used to analyze the structure features of POG-1A. The result showed that POG-1A wasa linear, unbranched polysaccharide containing a single type ofβ-D-glucose. Theβ-D-glucoselinked with (1→4)-O-linked β-glucopyranosyl unit and (1→3)-O-linked β-glucopyranosylunit. The ratio of β-(1→3)linkage and β-(1→4)linkage was 1:2.4. The relative amounts ofoilgosaccharides produced byβ-glucanohydrolase mainly were tri-(DP3) and tetrasaccharide(DP4). The total amount of tri-and tetrasaccharide was 90.91%. We observed the association ofPOG-1A directly using AFM. The result showed POG-1A was composed of cross-linked networkstructure and the structure afterβ-D-glucan-4-glucanohydrolase hydrolysis was polymerized .The solutions rheological behaviors and gelling properties of oat branβ-glucan wereinvestigated. Compared the apparent viscosity of β-glucan with guar,xanthan and CMC and thesynergism of interactions of oat β-glucan in binary with other gum(xanthan, guar and CMC) indifferent ratio at 0.5%. Oatβ-glucan was able to form gel. The gelling forming properties of oat β-glucan were investigated. All this result showed oatβ-glucan could use as thicken and gellingagent in food industry.Stability of foams and emulsions of oatβ-glucan were assessed . The concentration ofβ-glucan, temperature and pH had some effects on foam and emulsion stability. Compared of theemulsification properties of 5 hydrocolloid gums ( arabic, carrageenan, guar, xanthan and CMC )and measured the surface tension of water-air and interfacial tension of water-oil. The mainmechanism of foam and emulsion stabilization of oat β-glucan gum was mainly due to increasingviscosity and lowering interfacial tension. All these properties of oatβ-glucan shows potentialutilization value in food industry.Studied the effect of oatβ-glucan with different relative molecular weight on intestinal floraand its function in mice. A significantly increase of the numbers Bifidobacterium , lactobacilli anddecrease of Enterobacillus strains in groups containingβ-glucan(OG2600, OG340 and OG5)compared with the control. Results of this study demonstrated that oat β-glucan had the functionof regulating intestinal flora and the effect were related to molecular weight and dosage, the lowerof Mr and the higher dosage, the effects were better. It suggested that oatβ-glucan had prebioticeffects . In the large bowel, oatβ-glucan increased the fermentation activity, the productions oftotal short chain fatty acid(T-SCFA) were higher in the groups in three higher dosages comparedwith the control. Oatβ-glucan led to increase the production of propionate and butyrate(especiallyproduction of butyric acid) and decrease the acetate in colon. The production of SCFA enhancedgrowth and colonization of some probiotic bacterial strains, increases production of microbial mass .The pH in the intestinal contents and bodyweights were reduced in experimental groups, especiallyin group 2,this suggested oatβ-glucan of higher Mr have some effect of antinutrition. Oatglucan(OG2600) increased the viscosity of the small intestine , increased the number of goblet celland shorten the villus. Short-chain fatty acids formed enhance cell proliferation of the colonicmucosa epithelium.To evaluate the fermentability of oatβ-glucan in vitro, mice faeces were incubated in oatβ-glucan medium that contained 50 mg OG2600 or OG5 and fermented for 24 h. The amounts oftotal-SCFA in control and oatβ-glucan medium groups were 0.33,9.20 and 10.80mmol/g . In vitrostudies showed that oatβ-glucan was easily fermentation. The result was no more related tomolecular weight of oat β-glucan.Oat β-glucans and its hydrolyzate were as selective substrates for Bifidobacterium andLactobacillus strains. The main reasons were the fermentation , depolymerization and decreasingof pH in large bowel.