Adsorption and Electrokinetic Properties of Catalase onto Perlite Samples

Abstract

With immobilized or adsorbed enzymes or protein, many improved features such as stability, reusability, continuous process, control of reactions, more favourable economic factors can be expected. For this purpose, in this study, the adsorption properties of casein onto some oxide minerals such as unexpanded (raw) (RP) and expanded (EP) perlite samples were studied. The expanded perlite is obtained from the raw perlite when it reaches temperatures of 850–900°C (1,560–1,650°F). Raw perlite expands and softens after this heat treatment. The adsorption properties were studied as a function of concentrations of catalase, temperature, incubation time and pH of the aqueous solutions with both perlite samples. Similar experimental trends were found for the two perlite samples. According to the experimental results, the adsorption of catalase increases with increasing temperature and ionic strength of the solutions. The adsorption decreased with increasing pH. Maximum adsorption capacity values (qm) showed dependence on pH. It was observed that qe-pH curves reached a maximum at around neutral pH value. Furthermore, the electrokinetic properties of casein-covered oxide particles were also investigated at similar conditions to those of the adsorption process. However, the adsorption capacity of expanded perlite is higher than the raw perlite due to the increase in surface area. The nature of the adsorption process was investigated using Langmuir and Freundlich isotherm models. Three kinetic models, the pseudo first-order, second-order and intraparticle diffusion, were used to predict the adsorption rate constants. The study of temperature effect has been quantified by calculating various thermodynamic parameters such as activation energy, Gibbs energy, enthalpy and entropy. In addition, activity of free and adsorbed catalase were studied and calculated the Km and Rmax.