Background: Immobilization allows easy recovery and reuse of enzymes in industrial processes. In addition, it may enhance enzyme stability, allowing prolonged use. A simple and novel method of immobilizing β-galactosidase is reported. Effects of immobilization on the enzyme characteristics are explained. β-Galactosidase is well established in dairy processing and has emerging applications in novel syntheses.
Methods: β-Galactosidase was immobilized by physical adsorption on halloysite, an aluminosilicate nanomaterial. Optimal conditions for adsorption were identified. The optimally prepared halloysite-adsorbed enzyme was then entrapped in a porous matrix of nanocrystals of sulfated bacterial cellulose, to further enhance stability.
Results: Under optimal conditions, 89.5% of the available protein was adsorbed per mg of halloysite. The most active and stable final immobilized biocatalyst had 1 part by mass of the enzyme-supporting halloysite particles mixed with 2 parts of cellulose nanocrystals. Immobilization raised the optimal pH of the catalyst to 7.5 (from 6.0 for the native enzyme) and temperature to 55 °C (40 °C for the native enzyme). During storage at 25 °C, the immobilized enzyme retained 75.8% of initial activity after 60 days compared to 29.2% retained by the free enzyme.
Conclusion: The immobilization method developed in this work enhanced enzyme stability during catalysis and storage. Up to 12 cycles of repeated use of the catalyst became feasible.
General significance: The simple and rapid immobilization strategy of this work is broadly applicable to enzymes used in diverse bioconversions.
Keywords: Bacterial cellulose nanocrystals; Enzyme immobilization; Enzyme kinetics; Halloysite adsorption; β-Galactosidase.
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