Improving β-Galactosidase-Catalyzed Transglycosylation Yields by Cross-Linked Layer-by-Layer Enzyme Immobilization

Abstract

The biotransformation of lactose into gut-bioactive glycans catalyzed by β-galactosidase can give economic value to lactose-rich side streams generated in the food or the dairy industry. Herein, we study the immobilization of the commercially used β-galactosidase from Bacillus circulans onto silica particles using an enzyme immobilization technology involving a cross-linked layer-by-layer encapsulation method. The immobilized β-galactosidase was used for the synthesis of N-acetyllactosamine (LacNAc) as an important precursor for numerous bioactive compounds and a prebiotic in itself. Techniques including molecular analysis, enzyme activity determination, secondary structure analysis, thermodynamic characterization, and the determination of thermal and operational stability were conducted to characterize the immobilized enzyme. Changes in the activity of the enzyme after immobilization were attributed to possible changes in electrostatic, covalent, and protein–protein interactions. Immobilization significantly improved the enzymatic LacNAc yield compared to the free enzyme. In turn, this improved the economics and the sustainability of the process. The immobilized enzyme encapsulated in multilayer films was significantly more stable in the presence of divalent cations and its thermostability also substantially increased with the thermal denaturation activation energy increasing from 53 to 294 kJ mol–1. The immobilized enzyme was successfully reused in eight consecutive reaction cycles with no significant reduction in the LacNAc yield. The improved transgalactosylation yield and productivity, higher stability, and reusability obtained with this immobilization method provide new opportunities for industrial applications.