Screening And Fermentation Of β-galactosidase Producing Microorganism

Lactase, also known as β-galactosidase, which can hydrolyze lactose into glucose and galactose, is often used to produce low lactose food, is mainly used in the dairy industry, also has wide application in other fields. In this thesis,the screening,identification and fermentation of β-galactosidase producing were studied.Fifteen strains which produce β-galactosidase were screened from the soil of Dalian Sanhuan dairy plant using X-gal as indicator. The β-galactosidase activity was measured using ONPG as substrate, and the strain of MFY-03was selected among the above fifteen strains based on the β-galactosidase activity. The strain of MFY-03was used as the starting strain in all experiments.Physiological and biochemical experiments results of the strain MFY-03are as follows: G+, rod shaped, having spores, able to grow in5%NaCl medium, positive in movement experiment, negative in catalase test; hydrolyzed starch obviously, but not gelatin, V.P, M.R+can not use citrate, can utilize xylose, rhamnose sugar, glucose, lactose, mannose to fermentation acid, but no gas producted. Through the observation of colony morphology and16S rDNA sequence analysis, the strain MFY-03was identified as AcinetobacterThe fermentation conditions for β-galactosidase production by the strain MFY-03in shaking flasks were optimized. The optimal fermentation medium for β-galactosidase production was:1%glucose,1%lactose,0.5%yeast powder,1%peptone,1%Tween-80, and pH6.8. The flasks were incubated at45℃and200rpm for24h, and the β-galactosidase activity reached3.74U/mLThe optimum temperature and pH value for the β-galactosidase from strain MFY-03were55℃,6.8, respectively.The β-galactosidase was stable at less than55℃, and pH5.5-7.5. Metal ions with low concentrations had no significant effect on the enzyme activity, but high concentrated metal ions, especially Cu2+, inhibited enzyme activity strongly.