Selection Of γ-aminobutyric Acid-producing Lactic Acid Bacteria And The Development Of Functional Yoghurt

In this thesis, lactic acid bacteria which had the ability of synthesis of γ-aminobutyric(GABA) were isolated from traditional fermentative food products. The abilities of thestrains for producing γ-aminobutyric acid (GABA) were analyzed qualitatively andquantitively by using Thin Layer Chromatography (TLC) and High Performance LiquidChromatography (HPLC). The lactic acid bacteria with the high GABA productive abilitywere identified based on morphological characteristics, physiology biochemistryexperiment and16S rDNA sequence analysis. Finally, aiming to develop a new kind ofhigh GABA functional yoghurt, we utilised the high-GABA–productive lactic acidbacteria and the traditional yoghurt starter to produce yoghurt and examined its quality.The results were as follows:(1) the γ-aminobutyric acid content in lactic acid bacteria fermented liquid weredetermined by using improved HPLC method with o-phthaldialdelhyde pre-colomnderivatizatio-electrochemical detection.After centrifugation and pre-colomn derivatizationof fermentation liquid, the separation and detection of GABA in the liquid was carriedout on Luna-C18column (250×4.6mm,5μm)with the mobile phase consisted of15mmol/sodium acetate (pH5.8) and methanol (55:45), and the flow velocity was0.8ml/min,the column temperature was30℃, the detection wavelength was334nm. The resultsshowed that the content of γ-aminobutyric acid between50μg/mL~800μg/mL appearsgood linear relationship, and the linear equation was y=5465.9x–5411(R2=0.9996), and itsdetection limit was2.6714μg/mL.The average rate of recovery that had been added thespecimen is98.31%, RSD=2.27%. This technique was sample，convenient and highsensitive, showed good separation degree and high accuracy, and it was satisfied with thedemand of trace analysis.(2)22strains of lactic acid bacteria were isolated from traditional fermented products,The ability of these strains to produce γ-aminobutyric acid (GABA) were analyzed byusing Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography(HPLC). The results of TLC showed that14strains of LAB had the ability to synthesizedGABA, When these strains were cultured in MRS medium containing1%Glutamic Acidat37℃for48h; Through the quantitative analysis by HPLC, the strain QL-14（0.39g/L）and QL-20（0.584g/L）showed higher GABA-producing ability. Based on morphologicalcharacteristics, physiology biochemistry experiment and16S rDNA sequence analysis,the strain of QL-14was identified as Lactobacillus plantarum, and the strain of QL-20was identified as Lactobacillus casei.(3)Utilizing high-GABA–productive lactic acid bacteria and traditional yoghurtstarter to produce yoghurt and determining its quality. The results showed that theseyoghurt were cultured in skim milk containing0.5%sodium glutamate at37℃for6h, afteradding Lactobacillus casei.QL-20and Lactobacillus bulgaricus, Streptococcusthermophilus(1:2:1, inoculation amount was5%), it’s acidity was98.3°T，pH was4.38,lactic acid bacteria number was3.5×107CFU/mL, and GABA contents was0.2242g/L,tasted good and according with the national standard.