Screening And Application Of Microorganisms With High Production Of ?-aminobutyric Acid In Fish Sauce

Yu jiang suan is an unique traditional fermented condiment in Qian dong nan,Guizhou Province,China,which is fermented under natural conditions by using microorganisms carried by itself or in the environment,has high nutritional value,unique flavor and bright colors.However,the natural fermentation and the growth of harmful microorganisms during fermentation will cause a long fermentation period and reduce the safety of the product.On the other hand,the traditional fermentation methods do not have specific standards,making the quality of Yu jiang saun unstable and fermentation conditions uncontrollable,and difficult to complete product development and achieve industrial production.To solve the problems in the fermentation process and improve the quality of the product,screening out?-aminobutyric acid(GABA)-producing microorganisms from naturally fermented Yu jiang suan for its fermentation,through the separation of LAB in different fermentation stages of Yu jiang suan,thin-layer chromatography(TLC)and Berthelot colorimetric method were used to select target bacteria,and analyze the fermentation characteristics such as acid tolerance,bile salt tolerance,amino acid decarboxylase activity,antibacterial activity,growth curve,pH value,and the producing of acid.Inoculating and fermenting Yu jiang suan to observe the changes of quality during fermentation.GC-TOF-MS is used to determine the metabolites during fermentation of Yu jiang suan.Specific research results are as follows:(1)There were 15 typical GABA-producing strains obtained from 387 lactic acid bacteria(LAB)isolated and purified from different fermentation period of Yu jiang suan,including 2 strains of Weissella cibaria,1 strain of Weissella bombi,11 strains of Lactobacillus plantarum and 1 strain of Lactobacillus pentosus.Among them,the GABA production of Y113 was 0.239 mg/mL,which is higher than other strains.And the GABA production and fermentation characteristics of 15 LAB were significantly different in the principal component analysis chart.Y279 and Y64 were good at acid tolerance,bile salt tolerance,no amino acid decarboxylase activity,antibacterial activity,growth rate and the producing of acid.Due to its excellent fermentation characteristics,probiotic characteristics and GABA production ability,strain Y279 can be used as a potential excellent strain for industrial and standardized production of Yu jiang suan.(2)The screened Weissella cibaria Y113 and Lactobacillus plantarum Y279 were inoculated for fermentation.The strains dominate from the early period of fermentation,grow and multiply rapidly,producing organic acids and other beneficial metabolites.Compared with the natural fermented Yu jiang suan,the inoculated fermented one has higher content of LAB,amino acid nitrogen,TCA-soluble peptide,which can effectively promote the degradation of fish protein to produce small molecules of peptides,amino acids,organic acids and other nutrients for human absorption and utilization,while significantly inhibiting the production of nitrite,volatile salt nitrogen(TVB-N)and thiobarbituric acid(TBA),which improves the nutritional value and safety of the products and gives them better flavor and sensory quality.(3)GC-TOF-MS was used to investigate the types of differential metabolites and metabolic pathways during the fermentation of Yu jiang suan.A total of 26 differential metabolites were obtained for organic acids,sugars and their derivatives,amino acids and their derivatives,and alcohols and others according to the VIP values presented by the OPLS-DA model and the P values of the t-test to screen for differential metabolites between groups(VIP>1 and P<0.05).Among them,myo-inositol is with the highest variance multiplier,which would largely influence the quality of inoculated fermented Yu jiang suan.Differential metabolite species were enriched at the period of 4 to 12 days of fermentation,when Yu jiang suan fermented rapidly and accumulated large amounts of metabolites.Significantly related metabolic pathways were screened according to P<0.05 and Pathway impact>0.1.The fermentation process of Yu jiang suan mainly involved tricarboxylic acid cycle(TCA),pyruvate metabolic,glycolytic/glycoisomeric pathway and alanine,aspartate and glutamate metabolic.