Study On Culture Conditions And Enzyme Characteristic Of Aspergillus Oryzae β-Galactosidas

Lactase(lactase) is called β-D-galactoside galactose hydrolase(β-D-galactohydrolase),referred to as β-galactosidase (β-galactosidase), is a hydrolase. At present, β-galactosidasesare mainly used in food, medicine, environmental protection, biochemical analysis, genetherapy. But the domestic and foreign research shows that directly screened strains fromnature its enzyme activity is relatively low, the microbial solid-state fermentation, canimprove the lactase activity effectively. The Aspergillus oryzae UV-LiCl-38as the startingstrain, the subject studied the composition of the solid-state fermentation and fermentationconditions by using solid-state fermentation. The optimal fermentation conditions ofAspergillus oryzae UV-LiCl-38strain identified, and the characteristics of latctae werestudied, the condition of lactase production and the the main contents of the study were asfollowing.1.Through a single factor and CCD tests defined The optimized culture medium forβ-galactosidase production was obtained with wheat bran to nutritive media ratio of1:1, andcontain2.39%(w/w) lactose,1%(w/w) sucrose,0.56%(w/w) ammonium sulfat,0.5%(w/w)beef extract,1.8%(w/w) KH2PO4,0.5%(w/w) manganesium sulfate,0.5%(w/w) manganoussulfate. Fermented for5days, the β-galactosidase activity was188.92U/mL.2.Through a single factor and orthogonal tests defined the optimized culture conditionsfor lactase yield from Aspergillus oryzae UV-LiCl-38were as follow: the solid-to-liquid ratiowas1:1.5, initial pH5.0at30oC for5days using1ml spore suspension (106spores/ml) asinoculum’s size, the β-galactosidase activity was195.13U/mL, which was more34%than thebasic medium activity145.62U/mL.3.Lactase from Aspergillus oryzae UV-LiCl-38was salting out by ammonium sulfatefractionation; then study on its kinetic properties and its stability. The result showed that thethe specific activity of Aspergillus oryzae UV-LiCl-38was464.03U/ml by30～80%ammonium sulfate fractionation. The optimum pH of enzyme activity was obtained at5.5, thepH stability of lactase was4.5～6.0. The highest level of enzyme activity was obtained at50℃, at the temperature of40~55℃enzyme activity is the most stable, the variationamplitude of lactase was not obvious when keeping the temperature of heat preservation at30℃and40℃respectively, but at60℃and65℃the variation amplitude was obvious,placed at70℃for2h the live relative enzyme residue barely20%; The lactase activity wasactivated by Li+, Fe2+, Mn2+, Mg2+. Cu2+, K+, Zn2+, Ca2+, galactose, SDS, EDTA had inhication effect on lactase activity. The Km value and Vmax of this enzyme was1.61mmol/L1.78μmol/min.