Abstract
► AgNPs were synthesized, characterized and surface modified by glutaraldehyde. ► Aspergillus oryzae β galactosidase was adsorbed on unmodified and modified AgNPs. ► Immobilized enzyme was used for hydrolyzing whey and milk lactose. ► Operational stability of immobilized β galactosidase was also investigated.
The present study demonstrates synthesis, characterization and surface functionalization of silver nanoparticles (AgNPs) via glutaraldehyde for high yield immobilization of Aspergillus oryzae β-galactosidase. Soluble β-galactosidase (SβG), enzyme adsorbed on unmodified AgNPs (UβG) and surface modified AgNPs (MβG) showed same pH-optima at pH 4.5. However, it was observed that MβG exhibited enhanced pH stability toward acidic and alkaline sides, and increased temperature resistance as compared to SβG and UβG. Michaelis constant, Km was increased nearly three-folds for MβG while Vmax for soluble and MβG was 0.515mM/min and 0.495mM/min, respectively. Furthermore, MβG showed greater resistance to product inhibition mediated by galactose as compared to it soluble counterpart and exhibited excellent catalytic activity even after its fourth successive reuse. The remarkable bioconversion rates of lactose from milk in batch reactors further revealed an attractive catalytic efficiency of β-galactosidase adsorbed on surface functionalized AgNPs thereby promoting its use in the production of lactose free dairy products.