Optimized Production And Purification Of γ-Aminobutyric Acid Produced By Lactobacillus

Gama-aminobutyric acid (GABA) is a natural functional amino acid. It regulates over40% inhibitory synaptic activity in neural system and has positive functions to human healthlike anti-hypertension, enhancement of long-term memory, improvement of brain activity andhepaticprotective, nephriticprotective effects. Therefore, it can be widely used in healthyfoods as a new functional factor.By using Lactococcus lactis SK005, fermentation conditions for GABA production wasoptimized in flasks and a small scale bioreactor;then pilot scale was carried out in 20Lbioreactor to demonstrate the results of optimization of fermentation conditions;pretreatmentof GABA fermentation broth was conducted by using chitosan and active carbon;thetechnology of ion exchange for recovery GABA was studied;and pilot scale was carried outin 300L bioreactor to produce GABA. The main research content and results were as follows:1. This study established the optimal experiment scheme for GABA fermentation fromlactobacillus SK 005. By using the Orthogonal Design and the Analysis of Variance, theoptimal fermentation temperature, time and initial pH of culture medium were optimized. Theeffects of 6 major culture components, defatted soybean flour (DSF), L-monosodiumglutamate (L-MSG), corn steep liquor powder (CSLP), glucose, K2PHO4 and yeast extract,were analyzed by Orthogonal Design and Stepwise Regression. The dominant factors of finalresults were DSF, CSLP and L-MSG, respectively. Under the Central Composite Design andResponse Surface Analysis of these 3 major factors, the optimal medium components weredetermined. The result showed that the content of GABA was 5.4 g/L in the optimum culturemedium, which contained 5 g/L DSF, 21.8 g/L CSLP and 9.5 g/L L-MSG after fermentationfor 3 days at 30 ℃ and with the initial culture medium pH at 6.8.2. Pilot scale was carried out in 20L bioreactor to demonstrate the result of optimizationof fermentation conditions. The optimization of fermentation conditions can be amplified andthe main content of GABA fermentation broth was GABA 3.5~4.0 g/L,glutamic acid 2.5~3.0g/L,lactic acid 5.5~6.0 g/L,glucose ~0.3 g/L,protein 10g/L。3. Pretreatment of GABA fermentation broth was conducted by using chitosan and activecarbon. A series of experiments were carried out to optimize the parameters such as pH ,flocculant dosage and temperature, and the optimum flocculation condition were: pH 5.0,flocculant dosage 250 mg/L and temperature 40℃. Under the optimum flocculation condition,the flocculation ratio was 80%. The optimum conditions of active carbon decolor methodwere: the dosage of active carbon 1%, temperature 80℃, time 30min, pH 5.0. Under theoptimum condition, the decolor ratio were 92% and the losing ratio of GABA was 5%.4. The technology of ion exchange for recovery GABA was studied. Effects of factorssuch as pH and concent ration of GABA on absorption capacity were investigated by staticstate absorption experiment. The optimal operation conditions of exracting GABA were asfollowing: fermentation broth of pH 5, sample flow-rate of 1 BV/ h . Then the elution methodof two steps by using H2O and 2mol/ L NH3?H2O was determined.5. By adopting the whole technology to produce GABA in a pilotscale 300L bioreactor,the total recovery ratio is 64.2% and the final purity of GABA was 57%.