PRODUCTION AND CHARACTERIZATION OF BETA-GALACTOSIDASE FROM ASPERGILLUS-ORYZAE

A strain of Aspergillus oryzae producing extracellular β‐galactosidase that hydrolyzes lactose in whey and dairy products was selected. The crude lactase concentrates were prepared by both semisolid and submerged fermentation. Yields of the enzyme from semisolid fermentation were much higher than submerged fermentation. The crude enzyme hydrolyzed lactose efficiently in acid whey and 83% lactose hydrolysis was obtained at 55°C. However, the activity of the crude enzyme is greatly reduced in cow's milk. A. oryzae lactase was purified by ammonium sulfate fractionation, chromatography on DEAE‐cellulose, chromatography on CM‐cellulose, and DEAE‐Sephadex A‐50 column chromatography. The purified enzyme had an optimum pH of 5. The optimum temperature was 5°C, whereas, for the crude enzyme preparation, it was 55°C. The pH stability of the enzyme was between 3.5 and 8.0 at room temperature for overnight. The Michaelis constant is 0.77 mM for o‐nitrophenyl‐p‐D‐galactopyranoside (ONPG) and 50 mM for lactose. The values of Vmax are 55.6 μg/min/mg of protein for ONPG and 2.4 μg/min/mg for lactose. Metal ions in the range 0.01‐l mM and sulfhydryl reagent (0.01–0.1 mM of p‐chloromercuribenzoate) have no effect on the enzyme activity. Galactose inhibited competitively the enzyme activity, whereas glucose did not. Copyright © 1979, Wiley Blackwell. All rights reserved