Study On Fermentation Production And Separationand Purification Of γ-poly (glutamic Acid)

As a kind of biological macromolecules,γ-Poly(glutamic acid)(γ-PGA) is watersoluble, biodegradable, edible and non-toxic toward humans and the environment. Therefore,γ-Poly(glutamic acid) and its derivatives have been of interest in a broad range of industrial fields such as environment, medicine, food and cosmetics. The Production ofγ-Poly(glutamic acid) has been attracted more and more attention. In this study, a high- yield starin was separated and selected from foodstuff. The recovery ofγ-Poly(glutamic acid) from highly viscous culture broth was also investigated to increase the yield and purity ofγ-Poly(glutamic acid).Firstly, the best starin ofγ-Poly(glutamic acid) production named bai-10^-1-3-1 was gotten during the strain screening. And The effects of medium composition on yield ofγ-Poly(glutamic acid) were also examined. The optimum fermentation medium was obtained as follows: the suitable carbon source was 1% citric acid and 9% glycero; 20g/L L-gluatmine; 30 mg/L Mn²⁺. Under the conditions, the viscosity of culture broth was the highest. It could reach 576 MPa·s. In addition, a block of brown product was separated from fermentation liquor, and the productivity ofγ-Poly(glutamic acid) reached 19.2 g/L. Its molecular weight was about 460 000. UV, FT-IR and NMR were used to characterize the structure of product, and the results showed it wasγ-Poly(glutamic acid). However, it also indicated that the product contained impurities, because two more absorption peaks in the 1H-NMR spectra compared with references.Secondly, the methods of ultrafiltration and gel filtration chromatography were evaluated by comparing the yield and purity of products to solve the difficulties in extraction ofγ-Poly(glutamic acid). When it was room temperature and the pH of fermentation liquor was 3, the optimum ultrafiltration conditions were as follows: dilution ratio (v/v) between fermentation liquor and water l:5, pressure 0.2MPa. Under this condition, fermentation liquor could keep highly permeation flux and low viscosity. The rate of eluate reached 49.7 L·m^-2·h^-1. Compared with traditional dialysis method, the productivity ofγ-Poly(glutamic acid) was higher, which was 24.5 g/L. Meanwhile, the volume of ethanol in post-processing could be reduced 90%. The produce was characterized by UV and FT-IR, which indicated the purity ofγ-Poly(glutamic acid) was better. But it was dark and could not be tested by NMR, which indicated that the product contained impurities and needed further purification. When eluent was deionized water and the pH of fermentation liquor was 3, gel filtration chromatography conditions were optimized and the results were as follows: the gel was fine grain, the flow rate of eluent was 1mL/min, the sample load was 4mL. Under these conditions,γ-Poly(glutamic acid) was well separated from fermentation liquor. Retention time was only 19 min. The maximal concentration ofγ-Poly(glutamic acid) in eluent was 5.7g/L. Compared with traditional dialysis and ultrafiltration, the productivity ofγ-Poly(glutamic acid) was higher. The produce was ivory with good toughness. And the results of UV, FT-IR and NMR indicatedγ-Poly(glutamic acid) was purer. It proved the separation method of gel filtration chromatography was more outstanding.