Comparative adsorption of amylase, protease and lipase on ZnFe2O4: kinetics, isothermal and thermodynamics studies.

The role of enzyme engineering in biotechnology, biological and pharmaceutical process cannot be over emphasized. This study compared the adsorption of digestives enzymes; amylase, protease and lipase on to Zn-ferrite (ZnFe2O4). The metal ferrite was synthesized via a sol-gel technique and characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), Electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopy (FTIR). The adsorption was studied in a batch process and the data were subjected to kinetics and isotherm models. Characterization shows that the particle has a nanoporous structure, with pore sizes of about 5.4 nm and good magnetic properties. The FTIR data showed the presence of M-O bond, which is a characteristic of metal ferrites. The adsorption of the amylase, lipase and protease on ZnFe2O4 follow first-order kinetic model with rate constants increasing with concentration. The maximum adsorption capacities as revealed by the generalized adsorption isotherms are 7.20, 42.90 and 22.24 mg g-1 for amylase, lipase and protease, respectively, with cooperative binding. The Dubinin-Radushkevich model gave the maximum adsorption energies, E of 3.74 kJ mol-1 for amylase, 2.01 kJ mol-1 for lipase and 1.51 kJ mol-1 for the protease adsorption, showing that the process is physisorption dominated. The isotherms fit the adsorption data in the order of Freundlinch > Generalized > Guggenheim-Anderson-de Boer > Tempkin isotherm > Dubinin-Radushkevich. Thermodynamic study revealed a spontaneous adsorption process with increased entropy. ZnFe2O4, therefore, is a very good adsorbent for the purification of enzymes and can be used as a supporter for enzymatic process that required immobilization of the enzymes.