Biological Preparation Of γ-aminobutyric Acid By Lactococcus Lactis SYFS1.009

Gamma-Aminobutyric acid (GABA) is a non-protein amino acid and acts as an important inhibitory neurotransmitter in mammal brain. It regulates over 40% inhibitory synaptic activity in neural system and has bioactivities like brain function-enhancing effects, hypotensive, calming, liver and kidney function-benefit. GABA can be widely used in healthy foods.Fed-batch fermentation was studied and pilot scale was carried out in 200L bioreactor. Then enzymetic conversion for GABA by Lactococcus lactis subsp. lactis SYFS1.009 was researched, the effects of PLP and buffer salt on conversion was investigated.Under the intermissive fed-batch process, the intital L-MSG concentration was 5g/L, and the feeding substrate was added in 3 times at 24h, 48h, 80h, respectively. During cultivation pH was controlled by 6mol/L NaOH. Compared with batch fermentation the final content of GABA was 5.41g/L, L-MSG was 0.68g/L. After 110h the conversion rate of L-MSG was 94.5% and the yield of GABA was 29.6%. Fed-batch fermentation method could accumulate GABA as well as increase utilization of L-MSG.Investigation on the production of GABA by fed-batch fermentation in 200L bioreactor, the reslut showed that this method was feasible and reliable. The purity of GABA was 53%, moisture content was 8.6%, ash content was 1.8%. This technich has successfully been applied to guide production.GABA was prepared by L-glutamate decarboxylase from Lc. lactis SYFS 1.009. The influence of cell age, cell concentration, substrate concentration, buffer system, temperature and pH were studied. The optimum reaction system was 0.2mol/L HAc-NaAc buffer pH4.2, containing 10g/L lactic acid bacteria, 10g/L L-MSG and 0.1mmol/L pyridoxal phosphate (PLP), temperature 45oC, reaction time 15h. The cell could be reused four times under optimum condition.The effect of external coenzyme on kinetic constants at 45oC, pH 4.2 and the enflucence of buffer system were investigated. The results indicated that external PLP exerted a significantly high effect on Km, which decreased from 22.95mmol/L to 4.65mmol/L. However, there was no significant difference in Vmax. The buffer system could steady structure of enzyme as well as maintain system pH during reaction. The kinetic model obtained by computer aided simulation was: P=[6×10-4(E02S0)+2.204][1-exp(-0.282t)]. The simulated model expected results closely approximated observed data and could guide practice.