Modification of Immobead 150 support for protein immobilization: Effects on the properties of immobilized Aspergillus oryzae β-galactosidase.

We studied the modification of Immobead 150 support by either introducing aldehyde groups using glutaraldehyde (Immobead-Glu) or carboxyl groups through acid solution (Immobead-Ac) for enzyme immobilization by covalent attachment or ion exchange, respectively. These two types of immobilization were compared with the use of epoxy groups that are now provided on a commercial support. We used Aspergillus oryzae β-galactosidase (Gal) as a model protein, immobilizing it on unmodified (epoxy groups, Immobead-Epx) and modified supports. Immobilization yield and efficiency were tested as a function of protein loading (10-500 mg g-1 support). Gal was efficiently immobilized on the Immobeads with an immobilization efficiency higher than 75% for almost all supports and protein loads. Immobilization yields significantly decreased when protein loadings were higher than 100 mg g-1 support. Gal immobilized on Immobead-Glu and Immobead-Ac retained approximately 60% of its initial activity after 90 days of storage at 4°C. The three immobilized Gal derivatives presented higher half-lifes than the soluble enzyme, where the half-lifes were twice higher than the free Gal at 73°C. All the preparations were moderately operationally stable when tested in lactose solution, whey permeate, cheese whey, and skim milk, and retained approximately 50% of their initial activity after 20 cycles of hydrolyzing lactose solution. The modification of the support with glutaraldehyde provided the most stable derivative during cycling in cheese whey hydrolysis. Our results suggest that the Immobead 150 is a promising support for Gal immobilization.