Immobilization of β-d-galactosidase from Kluyveromyces lactis on functionalized silicon dioxide nanoparticles: characterization and lactose hydrolysis.

β-D-Galactosidase (BGAL) from Kluyveromyces lactis was covalently immobilized to functionalized silicon dioxide nanoparticles (10-20 nm). The binding of the enzyme to the nanoparticles was confirmed by Fourier transform-infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Functionalized nanoparticles showed 87% immobilization yield. Soluble and immobilized enzyme preparation exhibited pH-optima at pH 6.5 and 7.0, respectively, with temperature optima at 35 and 40°C, respectively. Michaelis constant (K(m)) was 4.77 and 8.4mM for free and immobilized BGAL, respectively. V(max) for the soluble and immobilized enzyme was 12.25 and 13.51 U/ml, respectively. Nanoparticle immobilized BGAL demonstrated improved stability after favoring multipoint covalent attachment. Thermal stability of the immobilized enzyme was enhanced at 40, 50 and 65°C. Immobilized nanoparticle-enzyme conjugate retained more than 50% enzyme activity up to the eleventh cycle. Maximum lactose hydrolysis by immobilized BGAL was achieved at 8h.