Studies Onβ-galactosidase Produced By Filamentous Fungi

This paper mainly dealt with screening, optimization of fermentation media and conditions, extraction, purification and characterization of j3-galactosidase produced by Aspergillus oryzae. 3-Galactosidase-producing strain Aspergillus oryzae A-UN5 18 was bred after being N~ ion implantation. The crude enzyme activity of the mutant reached 700U/L, about 40% compared to the original strain Aspergil/us oryzae A. The optimization of fermentation media and conditions for Asp. oryzae A-UN 5 18 were slected by single factor and uniform experiments. The optimum culture medium was: 3% wheat bran solution, lactose 0.5%, ammonium sulfate 0.5%, potassium dihydrogen phosphate 1%, manganese sulfate lmmol/L and pH 5.5. The optimum conditions were: inoculum size: 10%, temperature: 300C, rotation: 180 r/min and time: 96h. Thereby, the crude enzyme activity of A-UN5 18 reached 800U/L. The f3-galactosidase from Asp. oryzae A-1J7N5 18 was purified by centrifuging, ammonium sulfate precipitation and carboxymethyl cellulose chromatography. The activity of purified 13-galactosidase was improved 40-fold. The recovery and specific activity of the enzyme were 45.6% and 84.0 U/mg, respectively. By analyzing the characterization of the purified ~-galactosidase, the following conclusions could be made. The optimum reaction pH and temperature for the enzyme were 5.0 and 600C, respectively. The enzyme didn抰 lose its activity when heated for 30mm at 600C, which showed its higher heat stability. The enzyme activity remained 90% when stored at 40Cfor three months. The ,, value of 13-galactosidase for ONPG and lactose were 7.O8mmol/L and 24.8mmol/L, respectively. The extent of lactose hydrolysis for lactose and whey was 80% and 60% when treated by 13-galactosidase at 6U/mL for 72h.