Thermodynamic analysis of sol-gel transition of gelatin in terms of water activity in various solutions

ABSTRACT Sol–gel transition of gelatin was analyzed as a multisite stoichiometric reaction of a gelatin molecule with water and solute molecules. The equilibrium sol–gel transition temperature, Tt, was estimated from the average of gelation and melting temperature measured by differential scanning calorimetry. From Tt and the melting enthalpy, ΔHsol, the equilibrium sol‐to‐gel ratio was estimated by the van't Hoff equation. The reciprocal form of the Wyman–Tanford equation, which describes the sol‐to‐gel ratio as a function of water activity, was successfully applied to obtain a good linear relationship. From this analysis, the role of water activity on the sol–gel transition of gelatin was clearly explained and the contributions of hydration and solute binding to gelatin molecules were separately discussed in sol–gel transition. The general solution for the free energy for gel‐stabilization in various solutions was obtained as a simple function of solute concentration. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 685–691, 2015.