Adsorption isotherms and thermodynamics of α-lactalbumin on an anionic exchanger

The investigation of protein adsorption phenomena on solid surfaces is important for the development of purification processes. Knowledge of this equilibrium and the induced conformational changes of proteins is essential for its understanding. Thus, the adsorption behavior of α-lactalbumin (α-la) on an anionic exchange resin, Streamline® Q XL, at pH 7.4 and four different temperatures was studied. It was observed that the adsorptive capacity decreases with higher temperatures. Five isotherm models were fitted to the experimental data, where the Langmuir and Jovanovic models were the best. The Toth model was also reduced to the Langmuir model. The results indicated that the adsorption process is homogeneous, indicating Langmuirian behavior. Thermodynamic analysis based on the van’t Hoff equation shows a spontaneous, endothermal and entropy driven process. The process became more spontaneous at higher temperatures, possibly less endothermal and unfold of the protein structure caused a negative effect on entropy associated to α-la conformational changes and small ions binding to the adsorbent, reflected by the reduction of maximum adsorptive capacity of the adsorbent.