A strain of Aspergillus oryzae producing extracellular p-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 iu 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 DEAESephadex A-50 column chromatography. The purified enzyme had an optimum pH of 5. The optimum temperature was 5O"C, whereas, for the crude enzyme preparation, it was 55°C. The ~H'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-Dgalactopyranoside (ONPG) and 50 mM for lactose. The values of v max are 55.6 pg/min/mg of protein for ONPG and 2.4 Mg/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.
A strain of Aspergillus niger isolated from sugarcane fields, produced an extracellular transfructosylase in the culture medium. Sucrose and raffinose induced the production to the enzyme, which was purified by 138-fold. The optimum pH for activity and stability were 5.5 and 6.5, respectively. Its optimum temperature was 55°C. The enzyme hydrolysed sucrose rapidly and simultaneously formed fructooligosaccharides by transfructosylation.
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