Production and characterization of beta galactosidase ec 18.104.22.168 from aspergillus oryzae
Park, Y.K.; De-Santi, M.S.S.; Pastore, G.M.
Journal of Food Science 44(1): 100-103
A strain of A. oryzae producing extracellular .beta.-galactosidase [EC 22.214.171.124] 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.degree. C. The activity of the crude enzyme was greatly reduced in cow's milk. A. oryzae lactase was purified by (NH4)2SO4 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 50.degree. C but for the crude enzyme preparation, it was 55.degree. C. The pH stability of the enzyme was between 3.5-8.0 at room temperature for overnight. The Km was 0.77 mM for o-nitrophenyl-.beta.-D-galactopyranoside (ONPG) and 50 mM for lactose. The values of Vmax were 55.6 .mu.g/min per mg of protein for ONPG and 2.4 .mu.g/min per mg for lactose. Metal ions in the range 0.01-1 mM and SH reagent (0.01-0.1 mM of p-chloromercuribenzoate) had no effect on the enzyme activity. Galactose competitively inhibited enzyme activity whereas glucose did not.