Continuous Flow-culture Of Lactobacillus Brevis NCL912 For Producing Gamma-Aminobutyric Acid

Gamma-aminobutyric acid (GABA) is a nonprotein amino acid which is widely distributed in organisms. GABA has potential as a functional bioactive component in food and pharmaceuticals because of the well known physiological functions. In this thesis, the continuous flow culture of Lactobacillus brevis NCL912 for production of GABA was first carried out successfully with a self-assembly chemostat. The effect of dilution rate, kinetics of continuous flow culture and characteristics of cell growth and GABA production were investigated. The main contents were as below:1 Thin layer chromatography (TLC) is an analytical method in common use, usually includes five steps:spotting, separating, drying, spraying/immersing and color development. In this paper, TLC was modified with pre-staining method, which only consisted of 3 steps:spotting, separating and color development. The modified thin layer chromatography can be used for the analysis of amino acids. Compared to the classical thin layer chromatography, the improved method was more rapid and inexpensive, and the results obtained were more clean and reproducible. It is suitable for the qualitative testing of GABA2 A continuous culture method of Lactobacillus brevis NCL912 was developed for production of GABA. The effects of the dilution rate on the biomass, residual glucose and GABA yielding of the continuous culture were tested. The steady states could be reached when dilution rates were 0.08,0.10 and 0.12 h-1, and could not be in the dilution rates of 0.06 and 0.14 h-1. The results indicated that it is feasible to achieve the efficient production of GABA by continuous flow culture.3 The kinetic of continuous flow culture was investigated under dilution rates of 0.08,0.09,0.10,0.11 and 0.12 h-1. It was showed that the growth kinetic model of Lb. brevis NCL912 with glucose as the limiting substrate wasμ=0.1235Cs/0.9335+Cs and the kinetic model of continuous GABA production was QGABA=6.8625g/g-cell·h.4 The characteristics of cell growth and GABA production during the continuous flow culture were investigated. The results showed that the continuous culture method could improve the productivity of cell and GABA significantly in comparison with the fed-batch culture. The highest productivity of cell (83.5 mg/ L·h) was obtained at dilution rate of o.11 h-1 and the glucose/MSG consumption ratio maintained in a certain range while slumped dramatically at dilution rate of 0.12 h-1. The highest GABA concentration and productivity were 56.7423 g/L and 5.1068 g/L·h respectively that obtained at dilution rate of 0.09 h-1.