Novel and efficient method for immobilization and stabilization of β-D-galactosidase by covalent attachment onto magnetic Fe3O4-chitosan nanoparticles

A novel and efficient immobilization of beta-D-galactosidase from Aspergillus oryzae has been developed by using magnetic Fe3O4-chitosan (Fe3O4-CS) nanoparticles as support. The magnetic Fe3O4-CS nanoparticles were prepared by electrostatic adsorption of chitosan onto the surface of Fe3O4 nanoparticles made through co-precipitation of Fe2+ and Fe3+. The resultant material was characterized by transmission electron microscopy. X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry and thermogravimetric analysis. beta-D-Galactosidase was covalently immobilized onto the nanocomposites using glutaraldehyde as activating agent. The immobilization process was optimized by examining immobilized time, cross-linking time, enzyme concentration, glutaraldehyde concentration, the initial pH values of glutaraldehyde and the enzyme solution. As a result. the immobilized enzyme presented a higher storage, pH and thermal stability than the soluble enzyme. Calactooligosaccharide was formed with lactose as substrate by using the immobilized enzyme as biocatalyst, and a maximum yield of 15.5% (w/v) was achieved when about 50% lactose was hydrolyzed. Hence, the magnetic Fe3O4-chitosan nanoparticles are proved to be an effective support for the immobilization of beta-D-galactosidase. (C) 2009 Elsevier B.V. All rights reserved.