Immobilisation of fi-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 dia-minopolyethylene glycol (DAPEG) as a second polymer layer by conjugation of PDA with DAPEG without using any activating agent. The amount of immobilised fi-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 fi-galactosidase was 15 degrees 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 fi-galacto-sidase was increased upon immobilisation. Finally, the operational stability of the immobilised fi-galactosidase was studied for lactose hydrolysis in a continuous reactor. After 96 h continuous operation, the remaining activity of the immobilised enzyme was 94%.(c) 2022 Elsevier Ltd. All rights reserved.