Adsorption equilibrium of α-amylase in aqueous solutions

The influence of pH, ionic strength and temperature on the equilibrium of adsorption of alpha-amylase from Aspergillus oryzae on a hydrophobic (Duolite XAD-761) and an anion-exchange (Duolite A-568)polymer-based adsorbent was studied by moment analysis of the chromatographic peak responses in HPLC. The adsorption isotherms were also measured in batch experiments at different temperatures. Both systems show a nonlinear equilibrium within the concentration range studied, and the results were fitted to both the Langmuir and Freundlich equations. Enthalpies and entropies of adsorption were estimated from the equilibrium adsorption constant obtained both by the moment analysis and by the limit region of the Langmuir isotherm corresponding to Henry's law. The results show that the process of adsorption of alpha-amylase on the hydrophobic resin was exothermic, while the anion exchange process is endothermic.