The Research On The Pretreatment And Extraction Of ?-polyglutamic Acid From Fermentation Broth

Poly-?-glutamic acid(?-PGA),a special polymer that consisits of D-and L-glutamic acid,is different from the traditional oilrelated polymer.Given its merit of water-absorption and biodegradation,y-PGA is widely used in many fields including medicine,environment,agriculture,industry and food.Bacillus amyloliquefaciens YP-11 was chosen to ferment the y-PGA and the property of fermentation broth was measured.In fermentation broth,the amount of y-PGA,other amino acids,reducing sugar,total sugar,polysaccharide,residual glycerol were tested as 24.37 g/L,22.94g/L(73.01%dialysis removal rates),3.40 g/L,9.78 g/L,6.38 g/L,and 19.71 g/L respectively,under the original tested pH(7.04);the viscosity was 14.04 pa/s with the cell dry weight measured as 9.64 g/L.Stability of fermentation broth was studied under bacteria and storage temperature.The results showed that with storage time extended,the fermentation broth with bacteria suffered a y-PGA production lost(3.70 g/L),with a 15.18%lost rates and reduced PH to 6.The most obvious change was viscosity,which was tested to be only 3.68 pa/s,with a 73.79%lost rates.In contrast,the fermentation broth after sterilization was stable and suitable for y-PGA storage at a low temperature.The fermentation broth was sterilized by acidation and flocculation,and the conditions were optimizied by orthogonal test.The results showed that the obtained optimal sterilization conditions were 3%NaCl,6000 rpm,20 minutes centrifugation time,45 ? flocculation temperature,20 minutes flocculation time and pH figure as 3.Under the optimum extraction conditions,the rate of sterilization was measured to be 91.17%.Non-single organic solvent,methanol-ethanol fractional steps precipitation method,was first applied to extract y-PGA from the fermentation broth,while the extraction conditions-were optimized by response surface method.Also the effects of organic solvent precipitation multiple,pH and time on the y-PGA purity were observed by using Box-Behnken design(BBD)on the premise of preliminary consideration of single factor.The results under Design-Expert v8.0.6.1 software showed that the obtained optimal extraction conditions were the combination of organic solvent precipitation multiple 3.48,pH 8.13,and 7.30 hours.Under the optimum extraction conditions,the corresponding value of purity and extraction ratio of ?-PGA was 75.16%and 88.73%,and the predictive accuracy was 99.02%.In consideration of the loss rate of y-PGA,drying time and the color,the best drying method was freeze drying.The y-PGA purity of final extract was 75.16%.At the same time,the extraction contains 8.91%other amino acids and 0.11%polysaccharide.The molecular weight was 101.86-235.55 kDa.