Screening,Fermentation Condition Optimization And Application Of GABA-producing Lactic Acid Bacteria

γ-aminobutyric acid(GABA)has a variety of physiological functions,and plays a beneficial role in the prevention and treatment of depression,anxiety and other diseases.Synthesis of GABA by lactic acid bacteria is a hot research topic at present.In this study,lactic acid bacteria strains with GABA-production capacity were screened from traditional Chinese pickles and mutated by gas-liquid plasma.After optimizing the fermentation conditions of GABA,the pilot fermentation was carried out and the GABA was isolated and extracted from the fermentation liquid.Finally,the lactic acid bacteria strains were used to develop functional fermented drinks.The main research contents and results of this study are as follows:(1)Screening,identification and mutagenesis of GABA-producing lactic acid bacteria.Fifty lactic acid bacteria strains were isolated from traditional Chinese pickles,and three strains LBG-29,LBG-24 and LBD-14 with GABA-production capacity were screened by HPLC,among which LBG-29 had the highest GABA content,5.64±0.04 g/L.The three strains were identified as Levilactobacillus brevis by 16S rRNA.Their safety evaluation was high in vitro and they had the characteristics of acid and bile salt resistance and anaerobic environment tolerance.At the same time,the gas-liquid plasma mutagenesis was performed on L.brevis LBG-29,which has not been reported in any paper.After 10 minutes mutagenesis of L.brevis LBG-29,the mutant strain LBG-29-166 with an 4.37%(The yield increased by 18.81%under 5 L fermentation tank.)increase in GABA production was obtained.(2)Optimization of fermentation conditions for GABA production and its separation and extraction.The growth curve of L.brevis LBG-29 was drawn to determine that the 18 h bacterial culture solution was the fermentation seed solution.The optimal fermentation conditions for the strain were determined as follows:initial pH 4.7,fermentation temperature 33.5℃,sodium amino acid concentration 120 g/L,and inoculation amount 5%,and the yield of GABA was 57.95 g/L by batch fermentation in 5 L fermentation tank under pH control.Based on the optimal fermentation conditions,the GABA yield of LBG-29-166 was 68.85 g/L by batch fermentation in 5 L fermentation tank with pH control and the yield of fed-batch feeding fermentation was 86.31 g/L.The yield of GABA was 82.01 g/L in 100 L fermentation tank,then GABA was separated and extracted,and the total product yield was 50.65%,the product purity was 98.20%.(3)Study on the application of fermented fruit drink by GABA-producing lactic acid bacteria.Litchi was chosen as the fruit material,and the physicochemical properties of litchi juice fermented by the three GABA-producing lactic acid bacteria at 37 ℃ for 48 h were analyzed.The results showed that the number of viable bacteria increased significantly during the fermentation process and reached 8.7 log10 CFU/mL after fermentation.The radical scavenging ability of 2,2-diphenyl-1-picrylhydrazyl(DPPH)was increased by 53.31-59.05%and the ferric ion-reducing antioxidant power(FRAP)was increased by 49.19-67.48%.In addition,the content of total polyphenol was increased by 4.42%-6.80%and the content of acetic acid was not less than 0.49 g/L after fermentation.The fermentation of L.brevis LBG-29 and L.brevis LBG-24 also significantly increased the GABA content of fermented litchi juice,which reached 3.07 ± 0.10 g/L and 2.29±0.10 g/L,respectively.