| The strain Bacillus licheniformis CGMCC3336 was used as the original strain in this article,a synthetic medium and a semi-synthetic medium were used in the fermentation process to obtain the fermentation broth that with high yield y-PGA,and the fermentation broth which obtained from these two ways were used to do the downstream extraction work on y-PGA.In the experiment,traditional methods were abandoned in the industries,such as degerming by adjusting the pH and conducting alcohol precipitation with ethanol and other organic solvents,modern membrane separation process and the activated carbon decoloring technology were considered,to extract y-PGA.Here are main conclusions of this article.Taking the y-PGA fermentation broth obtained from synthetic medium fermentation,diatomaceous earth was selected as the filter cake and two times of suction filtration were proceeded to conduct filtration sterilization,the bacteria removal rate was 98.25%;the macromolecular polysaccharide produced in the fermentation was hydrolyzed by glucoamylase,the treatment condition is enzyme 1 0.1 mL/L,pH 5.5,50? processing for an hour;after that fermentation liquor was quickly heated to 89.66?,holding the temperature for 32.19min,then the protein was removed by the method of thermal denaturation,protein removal rate could reach 90.51%,the yield of y-PGA was 86.29%;Decoloured by powdered activated carbon,and the decolorization conditions are that:adding 6#activated carbon after diluted until the supernatant initial OD440 value reached 0.344,the addition amount is 1.5%,conditions:30? pH 5.5,60 min,the decoloring rate is 81.38%,the yield of y-PGA is 90.37%;small molecular impurities such as salts,reducing sugars,pigments and other small molecules in the fermentation supernatant were removed by ultrafiltration,choosing 50 kDa membrane package and conducted 4 times of ultrafiltration to elute and remove the impurities,the inlet pressure when concentrated was set at 25 psi,40?,the inlet concentration of the final concentrate was 40 g/L,then the concentrated solution was collected.Taking the y-PGA fermentation broth obtained from semi-synthetic medium fermentation,selection plate and frame filter sterilization process,adjusting the pH value to 6.0,choosing 1100 mesh filter cloth,the dilution multiples of the fermentation liquid was 2 times(about 20 g/L),diatomite:clay=2:1,the total addition amount of filter aid is 1.5%(w/v),under these conditions,the bacteria removal rate was 97.11%,the yield of y-PGA was 89.26%,the protein removal rate was 16.31%;the powdered activated carbon was once used to bleach,selecting 5#of activated carbon,the addition amount was 1.95%(w/v),the decolorization conditions:26.3?,77min,pH 6.0,the decolorization rate was 58.73%,the yield of ?-PGA was 87.61%;the glucoamylase was used to hydrolyze miscellaneous polysaccharides,selecting enzyme 1,the volume of addition was 0.1 mL/L,the saccharification conditions:pH 6.0,55?,60 min;adjusting pH 5.85 and quickly warmed the fermentation broth to 90.08?,keeping the temperature for 21.79 min,the protein removal rate was 86.12%,the yield of ?-PGA was 85.53%;Selecting 6#activated carbon for decolorization,the volume of addition was 1.6%(w/v),the decolorization conditions:pH 5.85,48.61?,81.56 min,this time the decolorization rate was 83.41%,the yield of ?-PGA was 84.63%;selecting 10 kDa ultrafiltration membrane to proceed ultrafiltration and separate small molecular impurities,and the liquid was ultrafiltrated for 5 times,the inlet pressure when concentrated was set at 25 psi,40?,the inlet concentration of the final concentrate was 40 g/L,then the concentrated solution was collected.Compared with microwave drying,spray drying and freeze drying,the methods of freeze drying to dispose the samples at last were contracted and its molecular weight was determined,the molecular weight of ?-PGA that obtained from synthetic medium fermentation was 5.62×105 Da,and the molecular weight of ?-PGA from semisynthetic medium fermentation was 3.92×105 Da.Then some hydrogels with these ?-PGA samples were prepared,the water absorbent rate of the hydrogel is 1804.23%,which proved the ?-PGA was valuable. |
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