Protein Ternary Phase Diagrams. 2. Effect of Ethanol, Ammonium Sulfate, and Temperature on the Phase Behavior of (S)-Ovalbumin

The phase behavior of (S)-ovalbumin in aqueous ethanol and (NH4)2SO4 solutions (pH 7.0) was investigated for temperatures ranging from 20 to 90 °C. The various morphologies observed were presented on ternary phase diagrams. At 20 °C, three morphologies were observed in aqueous ethanol: one-phase liquid, one-phase solid, and two-phase liquid and aggregate. Differential scanning calorimetry indicated that the (S)-ovalbumin denaturation temperature in buffer solution of 89.45 °C significantly decreased with ethanol addition and increased in the presence of (NH4)2SO4. As a result, a pastelike morphology was observed at moderate protein (3−30 wt %) and ethanol (20−40 wt %) concentrations when (S)-ovalbumin solutions were heated above 50 °C. In contrast, (NH4)2SO4 had a stabilizing effect on (S)-ovalbumin ternary structure and thus had little effect on (S)-ovalbumin phase behavior below the denaturation transition temperature. However, this salt encouraged solid phase formation once the denaturation transition temperature was reached. Keywords: Protein; ovalbumin; ethanol; salt; phase diagram