Screening Of ?-aminobutyric Acid-producing Lactic Acid Bacteria And Optimization Of The Fermentation Conditions

In this study,a strain of lactic acid bacteria with high GABA yield was selected from a variety of different fermented foods,and the medium and culture conditions were optimized to further increase the GABA content in the fermentation broth.A soy milk rich in GABA was prepared by mixing lactic acid bacteria with high GABA yield and direct-injection starter to produce sour milk rich in GABA.The specific content and results are as follows:Firstly,68 strains of lactic acid bacteria were isolated from different fermented products and qualitatively analyzed by thin layer chromatography.The results showed that 9 strains had the ability to produce GABA.Quantitative analysis of these 9 strains by Berthelot colorimetric method gave a strain of L-SZ303(7.605 g/L)with high GABA content.The strain L-SZ303 was identified as a Lactobacillus plantarum strain by morphological identification test and 16 S rDNA gene sequence analysis.Secondly,the optimal composition of the TYG medium for the production of GABA by fermentation was determined by single factor and orthogonal test analysis.The results showed that the composition of the optimal medium was:glucose 15 g/L,tryptone 25 g/L,sodium succinate 2 g/L,yeast powder 6 g/L,rice bran 6 g/L,L-????5 g/L.On the basis of this,the culture conditions were optimized by Box-Behnken's central combination design and response surface analysis.The results showed that the optimal culture conditions were:The initial pH was 6.8,the fermentation temperature was 36°C,and the fermentation time was 3 d.The test results have good reproducibility.After optimization,the GABA content in the fermentation broth can reach 13.375 g/L.Thirdly,the lactic acid bacteria L-SZ303 was used as the starting strain,after UV mutagenesis treatment,and after 10 consecutive passages,Comparing the traits and genetic stability,a genetically stable GABA strain L-SZ303 UV was obtained,and the GABA content in the fermentation broth reached 14.646 g/L.The GABA production was increased by 1.271 g/L compared to the starting strain.Fourthly,the selected lactic acid bacteria L-SZ303 with high GABA and the direct-injection starter were mixed and fermented for the development of GABA-rich sour milk,and its quality was investigated.The results showed that the addition amount of L-????was 0.5%,the temperature was 45°C,the fermentation time was 8 h,and the ripening time was 18 h.At this time,the acidity of sour milk was 94.4°T,the pH was 4.39,the number of live bacteria of lactic acid bacteria was 5.1×109 CFU/mL,the content of GABA was 4.80 g/L,and the taste was good,and the sensory score was92 points.