ABSTRACT:In this study, β-galactosidase (Aspergillus oryzae) was covalently immobilized onto aminated polyvinyl chloride (PVC) via glutaraldehyde coupling. Effect of immobilization conditions was investigated. The maximum obtained immobilization yield is 27 units g −1 while the maximum expressed activity is 12 μmol minThe optimum pH of the free enzyme was observed at 5.2, whereas the optimum pH of the immobilized one was schiffed to 4.4. The optimum temperature for both the free and immobilized forms was recognized at 60• C. A change in the temperature profile of the immobilized enzyme below 60• C was observed when response to the elevation temperature was less than that to the free counterpart. The K m and V max values of the free and immobilized β-galactosidase were found to be 52.03 and 123.1 mM, and 6.12 and 9.98 μ mol/min, respectively. Lactose hydrolysis, 500 mL of 100 mM concentration, was studied using 400 units of either free or immobilized enzymes at pH 6.0 and 60• C. Almost 80% hydrolysis percentage has been obtained after 6 h hydrolysis time with immobilized enzyme compared with 63% hydrolysis percentage obtained after 2 h for the free counterpart. Investigation of the operational stability at 40• C shows that the immobilized enzyme kept its activity for 5 h over 10 successive lactose hydrolysis cycles, which provides potentials for practical application in milk and whey hydrolysis. C