Study On The Fermentation And Extraction Technology Of Poly-γ-guluamic Acid

Poly-γ-glutamic acid was a compound of equal poly amino acid that consist of L- and D-glutamic acids throughγ-glutamyl bonds. Owing to its excellent characters including biocompatibility, biodegradability, non-toxicity and non-pollution,γ-PGA has been used in many areas such as environment, food, cosmetics and pharmaceutical.γ-PGA and its derivatives had a widely applications including being used as heavy metal absorber, bioflocculant, super absorbent polymers, food additive, drug carrier, sustained-release material and so on. The paper concentrated on the optimization of the strain L536's culture medium and conditions, the separation and purification ofγ-PGA and the initial application ofγ-PGA. Main results were as follows:By single-factor experiments and response surface methodology, the culture medium and conditions of the strain L536 outputingγ-PGA were optimized. The optimum culture conditions were as follows (g/L): NaCl 15, soybean flour 53, sodium citrate 16, sodium glutamate 40, NH4Cl 4.6, K2HPO4 0.625, MgSO4·7H2O 1.25, MnSO4·H2O 0.35, CaC12·2H2O 0.2, inoculation amount 3%(V/V), temperature 37℃, initial pH 7.0, broth's volume in shake flask 35mL/250mL, rotation speed of rocking bed 200r/min and culture time 48h. Under these condition, the yield ofγ-PGA was 25.81g/L, increased for about 1.5 times more than before.Compared the different methods of hydrolysis ofγ-PGA, the hydrochloric acid hydrolysis was adoptes and the optimum hydrolysis time was 24h. The optimum ethanol concentration was 2 times than the volume of fermentation broth. The effect of pH on the viscosity of fermentation broth and extraction ofγ-PGA was studied. Ultimately, the best route of extraction ofγ-PGA was determined.The concentration of pureγ-PGA was 88.6% by amino acid analyzers. By paper chromatography, UV and IR, the characterization of'γ-PGA was analyzed. The results showed that the polymer was only composed of glutamic acid. There was an absorption peak at 215nm by the UV scanning. The purifiedγ-PGA basically coincidented with that of the standardγ-PGA prepared by Meiji Pharmaceutical Co., Ltd through the IR chromatograph. It indicated the polymer wasγ-PGA.Flocculating conditions ofγ-PGA produced by Bacillus amyloliquefaciens L536 were investigated. The flocculating activity got highest at theγ-PGA concentration of 1.2g/ L and in the neutral pH. The flocculating activity was synergistically simulated by the addition of cations, Ca2+ was the optimum cation that remarkably promoted the flocculating activity. The results showed that the optimum flocculation conditions were CaCl2 of 0.09mol/L.γ-PGA had a high flocculating activity to some organic and inorganic suspension. In addition,γ-PGA can be used to keeping the fruits and vegetables fresh and increased the soil moisture.