Study On The Preparation Of ?-aminobutyric Acid By Lactobacillus Brevis

Gamma-aminobutyric acid(GABA)is a natural non-protein amino acid that widely exists in plants,animals and microorganisms.GABA possesses several well-known physiological functions,such as antihypotensive effect,keeping sedation,treatment of epilepsy,boosting fertility,controlling asthma,hormonal regulation,activating liver and kidney function,and raising memory.Thus,GABA has broad application prospects in food and pharmaceutical industries as a bioactive compound.Lactobacillus brevis,which had highly efficient conversion ability from L-glutamate to GABA,was screened in the previous work.In this study,cultural conditions of seed and fermentation media and the efficient bioconversion process of L-glutamate to GABA by L.brevis were optimized.In view of this,the isolation and purification of GABA from the bioconversion solution were conducted as a preliminary inquiry.1.The optimum culture condition consisted of temperature 30?,Initial pH 6.5,shaking at 50 r/min,and seed age 10?12 h.2.The key factors were investigated through the single factor experiments,Plackett-Burman experimental design and Box-Behnken design.The optimal fermentation medium was composed of sucrose 35 g/L,yeast powder 30 g/L,monosodium glutamate(MSG)50 g/L,sodium acetate 2 g/L,K2HPO4 2 g/L,MgSO4 0.2 g/L,(NH4)2SO4 0.2 g/L,citric acid 8.69 g/L,NaCl 0.3 g/L,lysine 0.015 g/L,VB,6.14 mg/L,VB1 6.00 mg/L,VB6 5 mg/L,and Zn2+0.80 mmol/L.Under the optimal medium,the yield of GABA reached 67.42 g/L,which was 12%higher than that before optimization.On this basis,a 5 L fermentor enlarge fermentation experiment showed that the GABA production was 15.84%higher than the initial medium.3.A model system of bioconversion of L-Glu to GABA by L.brevis resting cells was established using L.brevis resting cells and the reaction ratio equation followed the classic Michael is-Menten equation at low substrate concentration(0<S<80 g/L).The optimal bioconversion system was consisted of 50 g/L wet resting cells from 48-h cultivation,1.5 mmol/L Mg2+,0.1%Tween-80,0.1 mmol/L pyridoxal 5'-phosphate(PLP)in 0.6 mol/L L-glutamate-containing citric acid-sodium citrate buffer(pH 4.5)at 45? and 180 r/min.By 12-h bioconversion at the ratio of 240 g/L MSG to 80 g/L L-glutamic acid,the final production of GABA reached 202.18 g/L at the molar bioconversion ratio of 99.43%.4.The decolorizing conditions such as temperature,time,pH and amount of active carbon were mainly evaluated and optimum absorb wavelength of pigment at 420 nm was also determined.As a result of single factor and orthogonal experiments,the optimum decolorzation conditions were determined as follows:activated carbon dosage 1.0%(w/v),decolorization temperature 70?,pH value 6.0 and decolorezation time 30 min.Under the optimal conditions,both the decolorization ratio and recovery ratio of bioconversion reached 97.75%and 97.36%,respectively.5.A preliminary inquiry was performed for the crystallization technology of GABA.A simple and effective method of separation and purification was brought forward.The recovery of GABA in the whole progress was about 83.33%,and the purity of the ultimate production reached 97.76%.