Electrostatic immobilization of pectinase on negatively charged AOT-Fe3O4 nanoparticles

Enzyme immobilization on magnetic nanoparticles (MNPs) has been a field of intense studies in biotechnology during the past decade. The present study suggests MNPs negatively charged by docusate sodium salt (AOT) as a support for pectinase immobilization. AOT is a biocompatible anionic surfactant which can stabilize MNPs. Electrostatic adsorption can occur between enzyme with positive charge and oppositely charged surface of MNPs (ca. 100 nm). The effect of three factors, i.e. initial enzyme concentration, aqueous pH and AOT concentration in different levels was investigated on pectinase immobilization. Maximum specific activity (1.98 U/mg enzyme) of immobilized pectinase and maximum enzyme loading of 610.5 mg enzyme/g support was attained through the experiments. Initial enzyme concentration is significantly important on both loading and activity of immobilized enzyme, while pH and AOT concentration only affect the amount of immobilized enzyme. Immobilized enzyme on MNPs was recovered easily through magnetic separation. At near pH of immobilization, protein leakage in reusability of immobilized enzyme was low and activity loss was only 10–20% after six cycles. Since pH is associated with immobilization by electrostatic adsorption, the medium pH was changed to improve the release of protein from the support, as well. MNPs properties were investigated using Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR) spectroscopy, and Dynamic Light Scattering (DLS) analysis.