Hydrolysis of lactose in milk by Kluyveromyces lactis β-galactosidase immobilized in polyvinylalcohol gel

beta-galactosidase was immobilized to polyvinylalcohol hydrogel lens-shaped capsules, LentiKats (R). After immobilization, the enzyme retained 20% of the free-enzyme activity. We found that 0.1 mol.1(-1) Na2SO4, which is usually used for hardening of LentiKats (R), caused the inhibition of beta-galactosidase enzyme activity (after 60 min, it decreased to less than 1% of the initial value). Therefore, we successfully used 0.1 mol.1(-1) K2SO4 for this crucial step. The pH optimum for both immobilized and free forms of the enzyme was 6.0-6.5, optimum temperature was 48 degrees C. The immobilized enzyme was used for lactose hydrolysis in repeated batch mode in ultra-heat treated milk (4.7% w/v lactose) at 15, 30 and 45 degrees C. The entrapped enzyme retained 80% of the inicial activity (59 mu mol.min(-1)g(-1)) after 10 repeated batches at 30 degrees C without any change in the mechanical stability of LentiKats (R). During milk hydrolysis, production of galactooli-gosaccharides was also observed.