Immobilisation of β-galactosidase onto double layered hydrophilic polymer coated magnetic nanoparticles: Preparation, characterisation and lactose hydrolysis

The surface of polydopamine (PDA) coated magnetic particles was grafted spontaneously with diaminopolyethylene glycol (DAPEG) as a second polymer layer by conjugation of PDA with DAPEG without using any activating agent. The amount of immobilised β-galactosidase was found to be 49.7 mg g−1 support. The optimum pH for the free and immobilised enzyme was observed at 5.5 and 6.0, respectively. The optimal temperature for the immobilised β-galactosidase was 15 °C higher compared with the free counterpart. The apparent Km values for the free and immobilised enzymes were found to be 3.69 and 4.35 mmol L−1, with Vmax values of 7.72 and 5.54 U mg−1, respectively. Thermal stability of β-galactosidase was increased upon immobilisation. Finally, the operational stability of the immobilised β-galactosidase was studied for lactose hydrolysis in a continuous reactor. After 96 h continuous operation, the remaining activity of the immobilised enzyme was 94%.