The Study On Screening And Mutation Breeding Of High-yield γ-aminobutyric Acid Yeast Strains And Optimization Of Its Fermentation Conditions

Gamma-aminobutyric acid is an important inhibitory neurotransmitter in mammalian nervous system,with many physiological functions.GABA main reaction came from L- glutamic acid decarboxylation, the reaction catalyzed by L- glutamic acid decarboxylase, some microbes have decarboxylase activity,such as lactic acid bacteria, mold, yeast, etc..This study successfully screened γ- aminobutyric acid fermentation strain of Candida strains, fermentation broth GABA levels measured by HPLC. First of its UV and NTG mutagenesis, mutant strains after the response surface optimization experiments to determine the optimum fermentation medium composition and fermentation conditions.Ultimately, the use of wheat bran as organic nitrogen high-yielding GABA strains which is providing a theoretical reference for future research γ-aminobutyric acid health products. The main results are as follows:1. A dragon into a strain isolated from white strains producing GABA, named C2, through the identification identified as Candida.sp.In order to increase GABA production strains C2 by UV Mutation Breeding. Mutagenesis conditions:using UV lamp at 20 W irradiation distance 20 cm 50s. Mutants screened UV28, which GABA production was 1.122 g / L.To use of NTG on mutant strain UV28 mutation, mutagenesis conditions: NTG concentration of 0.8mg / mL, NTG treatment time 15 min. Mutants screened NTG17, which GABA production was 1.574 g / L.To complex by UV and NTG mutant strain UV28, in accordance with the best UV and NTG mutagenesis mutation breeding conditions, yielding mutants screened Y6, GABA production up to 2.561 g / L.2.By optimizing the fermentation medium with response surface experiments to determine the optimum fermentation medium of Y6 which GABA production of composition: sucrose 23 g / L, bran 65 g / L, L- glutamic acid 6 g / L, pyridoxal phosphate 0.5 mmol / L, K2HPO4 1g / L, MgSO4·7H2O 0.5g / L, NaNO3 3g, KCl 0.5g / L, FeSO4 · 7H2 O 0.01 g / L. Under these conditions, GABA production was 3.450 g / L.3.By response surface test, using the best optimization of fermentation medium Y6 fermentation conditions, determine the optimum fermentation conditions Y6: initial pH 4.5, temperature 28 ℃, speed 200 r / min, fermentation time 3.5 d. Under these conditions, GABA production was 4.300 g / L.4. 5L fermentation tank with liquid volume 3L fermentation medium, fermentation tank test for Y6 stirring speed of 150 r / min, the amount of dissolved oxygen was 75.0% before 48 h, the amount of dissolved oxygen was 50.0% after 48 h,the amount of air 7.0L / M, incubation time is 3.5d, the pH value for the control of the 4.5. Finally, the fermentation broth measured GABA production of about 4.630 g / L.