Phase behavior, thermodynamic and rheological properties of ovalbumin/dextran sulfate: Effect of biopolymer ratio and salt concentration

Abstract

The complexation between ovalbumin (OVA) and highly charged dextran sulfate (DS) was investigated employing phase behavior, zeta potential, confocal laser scanning microscope (CLSM), isothermal titration calorimetry (ITC) measurement, and dynamic rheometer analysis. The critical boundary pH values (pHc, pHϕ1, pHmax) were strongly dependent on the biopolymer ratio and salt concentration. Results of the phase diagram and zeta potential showed that the formation of complexes was mainly driven by strong electrostatic interactions. As the increase of the OVA/DS ratio, the critical pH values shifted to higher values. However, the addition of NaCl has a diverse effect, lower salt concentration (CNaCl <100 mM) promoted the formation of OVA/DS coacervates, while higher salt concentration (CNaCl≥ 100 mM) suppress the formation of coacervates due to the shielding effect. The ITC results revealed that DS does bind to native form of OVA at pH 7.0 through the electrostatic forces and it was a spontaneous exothermic process (△G < 0, △H < 0). Additionally, much higher viscoelasticity (G'&G″) for all OVA/DS coacervates indicates that the formation of a highly interconnected gel-like structure. The maximum viscoelasticity was shown at an OVA/DS ratio of 10:1 with 50 mM NaCl. On the other hand, the addition of salt decreased the gel transition temperature of OVA thus promote its aggregation in the mixing system. Our work provides important insight for understanding the interaction between sulfated polysaccharide with egg white protein.