Selection Of Lactic Acid Bacteria For Producing γ-Amino Butyric Acid And Study On Fermentation Technology

The study mainly investigated the method for detection ofγ-aminobutyric acid (GABA), the breeding of GABA-producer 35# and the optimization of medium contents and fermentation conditions for 35#. Its contents and results are as follows:The method for detection of GABA was investigated in the beginning of this study. The paper chromatography accompanying colorimetry was used to measure the concentration of GABA. Then the composition of exhibition layer system and color system included in paper chromatography was determined. The best ratio of the exhibition layer agent was butanol: acetate:water (V/V) =2:1:1, and the proper concentration of coloring agent ninhydrin was 8g/L. It was found that the there was evident difference between Glu and GABA on Rf, which signified the condition for isolation was the best. And then we determined the best analytic conditions: the wavelength at 513nm, chromogenic temperature at 80℃, chromogenic time 30min, preserving time of eluent 30min. The relation curve of GABA content and OD513 was made out, which was also called standard curve of GABA and provided reliable experimental data for detecting the GABA content in samples. Furthermore, the repeated test and value add recovery rate of the sample was carried out. It turned on that using paper chromatography and colorimetry to quantitatively analyse GABA had a better repeatability, and the relative standard deviation was only 0.27%, meanwhile, the average value add recovery rate was 98.1%. These results signified that this method had higher reliability, which provided favorable base for the further study.In this study, a wilding bacterium (lactobacillus 35#) was isolated from pickled vegetable, which could transform L-MSG to GABA, and the GABA content of the culture reached 1.85g/L. Then the morphological characteristic and physiological characteristic of lactobacillus 35# was studied. After 2 days cultivation on MRS medium at 30℃, the germ was small, round, ivory-white and opaque, it was swelled up in the center, the edge was tidy, the periphery contained small crease, the surface was moist and smooth. It was found by its classification that the strain was a G+, facultative anaerobes, making the litmus red, glutin test negative, H2S test negative, V-P test positive, catalase test negative, indole test negative, M-R test positive, it produced acids but no gas by glucose zymolysis; sucrose, fructose, lactose, mannose test positive; the optimum growth temperature at 28~34℃, the optimum growth pH at 6.5~7.5. Basing on the Bergey's Manual of Systematic Bacteriology, this strain was preliminarily identified as Streptococcus lactis.The experiment optimized the culture medium and conditions for lactobacillus 35#. Based on the results, a piece of better medium constitution as follows(g/L): sucrose 10, sodium succinate 10,tryptone 5, yeast extract 5; L-MSG 10; and the better fermentation conditions as follows: initial pH6.5, temperature 32℃, seed volume 8%, fermentation time 48h, which is less than other internal study for 24h. The content of GABA was over 4.57g/L in the optimum culture conditions, there was prominent improvement on the yield.