Preparation and Characterization of PVA-SA Hydrogel Immobilized β-Galactosidase With Improved Catalytic Properties

This study reports the immobilization of Aspergillus oryzae β-galactosidase in a polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel and its performance compared with the free enzyme. Through immobilization, the optimum temperature shifted from 40°C to 60°C, with the immobilized enzyme retaining high activity and exhibiting improved resistance to heat-induced inactivation. Although maximum catalytic activity was observed at pH 5.0 for both free and immobilized forms, the immobilized enzyme sustained higher stability in near-neutral and slightly alkaline environments. Kinetic analysis revealed that the K_m value increased from 0.21 to 0.33 mM, indicating diffusion limitations, whereas the apparent V_max rose from 0.40 to 1.71 U/mg protein. Storage experiments demonstrated improved stability at 4°C, with about 60% of the initial activity retained after 8 weeks, whereas freezing at -20°C accelerated inactivation. The immobilized enzyme retained more than 80% of its catalytic performance after three consecutive uses and still preserved approximately 65% following the fourth cycle. Lactose hydrolysis experiments confirmed efficient and sustained performance, reaching 78% conversion after 180 min.