Studies On Fermentation And Kinetics For γ-Polyglutamic Acid

γ-Poly glutamic acid (γ-PGA) which can be produced by microbial, is a kind of biodegradable high molecular polymer.γ-Polyglutamic acid(γ-PGA) is a biopolymeric product exhibiting water solubility, biodegradation, edibility and non-toxicity to human and environment, making its wide application in many fields as food, cosmetics, medicine, agriculture and water treatment in the past decades.In this work, in order to improve production ofγ-polyglutamic acid, it was produced by Bacillus subtilis NOBEL-007, and the optimization of conditions of fermentation process were investigated. The production ofγ-PGA and biomass were greatly influenced by the composition of medium and culture conditions according to the results attained in flask liquid fermentation experiments, which were conducted to investigate the optimal process parameter forγ-PGA production. The highestγ-PGA yield was achieved in the conditions that describe as following: glucose 40g/L, yeast extract paste 5g/L, L-sodium glutamate 30g/L, NH₄Cl 3g/L, K₂HPO₄ 2g/L, MgSO₄ 0.25 g/L; inoculum level 2%, volume level 40mL (250mL flask), temperature 37℃, rotate speed 200r/min, nitial pH 7.0 and culture time 48 h, then the yield ofγ-PGA reached 20.15 g/L.The characterization ofγ-PGA from B.subtilis NOBEL-007 was investigated by the paper chromatography, FT-IR and NMR. The paper chromatograph obtained from hydrolysate of tested polymer was only one peak and was coincident with the chromatograph of glutamic acid. It indicated the polymer was composed of glutamic acid. The FT-IR chromatograph of the polymer showed no difference from that ofγ-PGA standard sample. It indicated the polymer was likely to beγ-PGA. NMR chromatograph further proved that the polymer consisted of glutamic acid.In order to further kown the character of Bacillus subtilis NOBEL-007 and improveγ-PGA production in batch fermentation, the effects of different fermenatation conditions, such as pH, temperature, rotate speed and aeration rate was investigated with regard to cell growth andγ-PGA production in 5L jar fermentor scale. The final optimal conditions were determined as followed: pH 7.0, cultivation at 37℃, strring rate 200r/min and aeration rate 1.0vvm. The highest productivity ofγ-PGA (22.16g/L) could be abtained under the above optimal conditions.On the basis of Logistic and Luedelting-Piret equation and the experimental data of batch fermentation in the 5L fermentation reactor, the mathematical models were proposed to describe the fermentation process with Bacillus subtilis NOBEL-007. The parameters of the models were established by using MATLAB software with experimental data and the models.The modes consist of: Cell growth model: Production formation model: Substrate depletion model:The above models could fit the profiles of cell growth, production formation and substrate depletion well. It might be helpful to understand and guide further optimization of PGA fermentation in the future.we synthesized the flocculation activity of ploy(γ-glutamic acid)(γ-PGA) produced by Bacillus subtilis NOBEL-007.γ-PGA showed high flocculation activities in kaolin, activated carbon suspensions, and the flocculation activity ofγ-PGA is steay to hot, but began to decrease upon heating at 70℃. In activated carbon suspension, theγ-PGA flocculating activity attained upon 90% at concentration of 10mg/L, and the flocculating activity synergistically increased by the addition of metal cations such as Mg²⁺, Ca²⁺, Na⁺ and Fe³⁺, Ca²⁺ was the optimum cation that remarkably promoted the flocculating activity; while adding Al³⁺, Fe²⁺ was disadvantageous to them. Using Ca²⁺ cloud lower the cost by dropping the dosage ofγ-PGA, but the excessive Ca²⁺ could obviously restrain the flocculating activity ofγ-PGA. The flocculating activity ofγ-PGA could be improved by adding 10mM Ca²⁺ to the suspensions and keeping the solution netural pH value. Futhermore, the distribution of bioflocculant ofγ-PGA was also researched, the flocculating activity was tested main in culture broth and supernatant, while the flocculating activity of cells was always low. Through synthesizing the correlation ofγ-PGA concentration and the flocculation activity of culture, we could conclude thatγ-PGA was the factor which caused the flocculation in the cluture.