Protein Ternary Phase Diagrams. 1. Effect of Ethanol, Ammonium Sulfate, and Temperature on the Phase Behavior of Type B Gelatin

The effect of ethanol or (NH4)2SO4 addition on aqueous gelatin solution (pH 7.0) phase behavior was examined in the temperature range from 10 to 70 °C for protein and solute concentrations of 0−100 wt %. Ternary phase diagrams were used to effectively illustrate the relationship between the seven protein morphologies observed. Gelatin only exists as a random coil structure above 40 °C. As a result, in ethanol and salt systems below 30 °C, one-phase or two-phase gel and liquid morphologies dominated. In contrast, above 50 °C, one-phase sol or two-phase coacervate morphologies occupied significant portions of the two phase diagram systems. Between 30 and 50 °C, a wide range of morphologies was observed in both systems, as the gelatin gradually transformed to a more random structure. Differences observed between the various gelatin phase diagrams were a result of altered protein−solute, intraprotein, and interprotein interactions caused by changing temperature, ethanol, and (NH4)2SO4 concentrations. Keywords: Protein; gelatin; ethanol; salt; phase diagram