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)(2)SO4 solutions (pH 7.0) was investigated for temperatures ranging from 20 to 90 degrees C. The various morphologies observed were presented on ternary phase diagrams. At 20 degrees 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 degrees C significantly decreased with ethanol addition and increased in the presence of (NH4)(2)-SO4. As a result, a pastelike morphology was observed at moderate protein (3-30 wt %) and ethanol (20-40 at %) concentrations when (S)-ovalbumin solutions were heated above 50 degrees C. In contrast, (NH4)(2)SO4 had a stabilizing effect on (S)-ovalbumin ternary structure and thus had little effect an (S)-ovalbumin phase behavior below the denaturation transition temperature. However, this salt encouraged solid phase formation once the denaturation transition temperature was reached.