Analysis of water sorption behavior of native and denatured proteins by solution thermodynamics.

Water sorption isotherms of native and denatured ovalbumin samples were measured, and their affinity for water was quantitatively analyzed by solution thermodynamics. The structural change of the proteins was evaluated by several methods. Water activity above 0.9 was measured by adding a specific amount of water to a sample, while that elbow 0.9 was measured with apparatus for water sorption isotherms. Thus, water sorption isotherms for native and denatured ovalbumin samples were obtained up to a water activity of 0.99. The water sorption behavior of ovalbumin was affected not by its hydrophobicity but by its prominent conformational change. It was confirmed that parameter delta Gs calculated by solution thermodynamics was more suitable for evaluating the affinity for water from water sorption isotherms than delta Gws calculated by conventional adsorption thermodynamics.