Screening Of ?-aminobutyric Acid-producing Lactic Acid Bacteria From 'Douchi' And Its Mixed Ferment-ation With Monascus

Douchi is well known and popular in China since ancient time. It's not only a kindof traditional fermented condiment, but also used as a kind of medicine. Huangyao lies inthe subtropical region where its climate belongs to subtropical monsoon climate. Itsunique geographical and cultural environments provide a good condition for HuangyaoDouchi manufacturing technique. These traditional fermented Douchi contains richmicrobial resources, especially it has a large number of lactic acid bacteria in thesecondary fermented process. In this study, the lactic acid bacteria with the ability ofproducing ?-aminobutyric acid(GABA) were isolated from Huangyao Douchi by thecombination of traditional pure culture methods and molecular biological methods.Firstly,16strains were isolated from Huangyao Douchi. By using HPLC method,GABA contents in the fermented broth were analysizd quantiviely. It was found that thestrain of HY15had the highest GABA-producing ability (the yield of GABA is161.25?g/mL). Based on morphological characteristics, physiological and biochemicaltests, and16S rDNA sequence analysis, the strain was identified as Pediococcus pento-saceus.Secondly, one-way analysis and orthogonal design were used to optimize the strainPediococcus pentosaceus HY15fermentation conditions to produce GABA. The effectsof the medium initial pH, fermentation time, cultivation temperature, monosodiumglutamate (MSG) concentration and pyridoxal phosphate (PLP) concen-tration on theGABA yield were studied. The optimum conditions were as follow: MSG concentration1%(W/V), initial pH6.0, fermentation time84h, concentration of PLP0.20mg/mL,fermentation temperature32?. Compared with161.25?g/mL of GABA under nonop-timum conditions,300.00?g/mL of GABA was achieved under optimum conditions.Finally, by mixed fermentation of Pediococcus pentosaceus HY15and Monascussp.M3, GABA production was investigated. The results showed that the obvious synergywas observed during the GABA-production of Pediococcus pentosaceus HY15and M3,but M3growth was not affected by Pediococcus pentosaceus HY15during co-cultivation.By the optimization of Response Surface Methodology, the results showed that optimumconditions for GABA-production were as follows: rotating speed150rpm, initial pH5.51and inoculation level for M31.5%(V/V). Under optimum conditions,248.06?g/mLof GABA was achieved.