Immobilization of β-galactosidase by bioaffinity adsorption on concanavalin A layered calcium alginate–starch hybrid beads for the hydrolysis of lactose from whey/milk

Aspergillus oryzae β-galactosidase was immobilized on the surface of a novel bioaffinity support: concanavalin A layered calcium alginate–starch beads. The maximum activity of the immobilized β-galactosidase was obtained at 60 °C, approximately 10 degrees higher than that of the free enzyme. The immobilized β-galactosidase exhibited significantly higher stability to heat, urea, MgCl2, and CaCl2 than the free enzyme. An enhancement of the activity of immobilized β-galactosidase by up to 5.0% MgCl2 was seen, whereas the activity of the free enzyme decreased above 3.0% MgCl2. Immobilized β-galactosidase retained 61%, 50% and 43% activity in the presence of 5% CaCl2, 5% galactose and 4 m urea, respectively, when incubated for 1 h at 37 °C. The immobilized β-galactosidase had a much higher Kiapp value than the free enzyme, which indicated less susceptibility to product inhibition by galactose. The immobilized β-galactosidase preparation was superior to the free enzyme in hydrolysing lactose in whey or milk in a batch process: it hydrolyzed 89% of the lactose in whey in 3 h and 79% of the lactose in milk in 4 h. The immobilized β-galactosidase retained 61% of its original activity after 2 months storage at 4 °C, while the soluble enzyme showed only 37% of the initial activity under identical conditions.