The Screening And Identification Of LAB Strains Isolated From Traditional Dairy Products With γ-aminobutyric Acid Producing And Optimizing Their Fermentation Conditions

9 LAB strains with relative high production ofγ-aminobutyric acid were screened from 180 strains isolated from traditional fermented dairy products using Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC). They were WH11-1(2.477g/L), M10-4-3(1.405g/L), WZ20-2(1.132g/L),WZ1-2(1.115 g/L), M11-3(1.006g/L),S1-1(0.581g/L), M5-1-1(0.310 g/L), M11-2-1(0.225 g/L)and M11-1(0.211 g/L).According to the traditional morphological characters, physiological and biochemical properties, as well as chemical characteristics, WH11-1,M10-4-3,M1-2,M11-3 and WZ20-2 was identificated as L. lactis subsp. Lactis, S1-1, M5-1-1 and M11-2-1 as L. plantarum,M11-1 as L. salivarius.Based on traditional identification, the genes of 16S rDNA were amplified in vitro and sequenced. Then a phylogenetic dendrogram was constructed by comparing the two sequences with other 16S rRNA/DNA sequences of Lactococcus. The results indicated that the homology of WH11-1 with L. lactis subsp Lactis NCDO604 was 99.1%, and the similarity of M10-4-3 with L. lactis subsp Lactis NCDO604 was 100%. Combined with analysis of the phyolgenetic tree and partial sequences of 16S rDNA , WH11-1 and M10-4-3 belonged to L. lactis subsp Lactis.In order to optimize the fermentation condition of L.lactis subsp Lactis WH11-1, different factors which had effect on production ofγ-amino butyric acid, such as the inoculating amount, initiational pH, culture temperature, culture time, ingredients of medium and the consistency of monosodium glutama,were studied. By single factor analysis,Response surface analysis(RSA) and orthogonal design experiment,the optimal cultivation conditions and optimal medium components were determined. The results showed that the content of GABA was 10.78 g/L in the optimum cultivation conditions, which were inoculation volume 4.5%, the initiation pH at 6.0 ,for 96h at 32℃;and the optimum culture medium , which were constituted by 2% total carbon,the ratio of glucose and alsace gum 3:1, soy peptone and yeast extract 1:3, total carbon and nitrogen 1:2, 0.15% pyridoxal phosphate, and 30g/L L-monosodium glutamate. The content of GABA was increased ahout 4 times than before.