β-galactosidase enzyme was isolated from Aspergillus niger, and immobilized in sodium
alginate gel. The maximum activity of the free enzyme was obtained at 65oC, pH 3.5 and its not
affected by immobilization. The free enzyme had pH stability range from 3.5 to 6.5 and it was
increased by immobilization process especially at acid pH values. The free enzyme retained
90.28, 85.09, 45.49, and 19.2 % of its initial activity after incubation at 30, 40, 50, and 60oC, for
60 min respectively. Thermal stability was enhanced by immobilization process. The kinetic
parameters for soluble and immobilized enzyme were also determined, and immobilization led
to decrease in Km value (5.12 mM for free form to 1.48 mM for immobilized form), indicating
decreased affinity by the enzyme for its substrate. Vmax was also decreased by immobilization
process, and it was reached from 86.66 μmol ONP.min-1 for free enzyme to .38.02 μM
ONP.min-1 for immobilized form.