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Production of γ-Aminobutyric Acid by Immobilized Streptococcus Salivarius Subsp. Thermophilus Y-2

Author: JiaoYang
Tutor: LuZhaoXin
School: Nanjing Agricultural College
Course: Fermentation Engineering
Keywords: S.salivarius subsp. thermophilus Y-2 immobilized cells GABA packed bed reactor
CLC: Q814
Type: Master's thesis
Year: 2009
Downloads: 35
Quote: 0
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Abstract


Gamma-aminobutyric acid (GABA), serves as a major inhibitory neurotransmitter in mammalian nervous systems. GABA has several physiological functions such as hypotensive activity, treatment of epilepsy, tranquilizing and allaying excitement, enhancing memory, controlling asthma, promoting reproduction and activating liver and kidney function. Production of GABA by Streptococcus salivarius subsp. thermophilus, which generally recognized as safe food additive, has been among the most remarkable research focuses in the realm of biology. To extend the application of immobilization technique in this bioconversion, the calcium alginate encapsulated cells of Streptococcus salivarius subsp. thermophilusY-2 for dissimilating MSG to GABA was researched. The main research findings are as follows:1. The strain was adsorped on resins and embedded in carrageenan, gelatin and calcium alginate. By comparing with each other in the glutamate decarboxylase (GAD) enzyme activity, mechanical strength of the carriers and operation stability, the calcium alginate was selected as better carrier for immobilization.2. Firstly, the sodium alginate concentration, calcium chloride concentration, microbial concentration and immobilized beds diameter were studied by single factor test. Then, according to the result of single factor test, condition of immobilization was optimized by orthogonal experiment. The optimal immobilization condition forγ-aminobutyric acid production was immobilized beds diameter 1.64mm, sodium alginate concentration 2%, calcium chloride concentration 16% and microbial concentration 20%.3. The technology of GABA synthesis by treated MSG with immobilized S.salivarius subsp. thermophilus Y-2 cells was developed. The effects of pH, temperature, supernatants, the concentration of calcium chloride, and the concentrations of MSG on the biotransformation were systemically investigated. As a result, the optimal pH, temperature for the biotransformation was 3.8,40℃, and the optimal reaction system was composed as following:Triton X-100 0.1%(V/V), MSG 40mM and calcium chloride 1.25%. In the condition, the final concentration of GABA in the reaction system was 2.79g/L, transformation efficiency was 66.57%.4. Comparing the effect of H/D and substrate solution flow rate on continuous operation transformation efficiency, the packed bed reactor with 6.2 H/D ratio and substrate solution flow rate in 5mL/h were chosen. Under the optimized reaction conditions, the packed bed reactor was operated for 192 h, average productivity was 2.2g/L/h.

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