Effect of pressure on the sol-gel transition of gelatin.

The effects of hydrostatic pressure on the sol-gel transition of gelatins were studied in the concentration range 1.5-12.5% under high pressures up to 300 MPa. The gelatin gels were stabilized by pressure: the pressure-induced elevation of melting temperature, (dT/dP)m, was 3.89 x 10(-2), 3.17 x 10(-2) and 2.92 x 10(-2) K/MPa for gelatins of Bloom No. 60, 225 and 304, respectively. The enthalpy, entropy and volume changes accompanying the gel formation were calculated from the Eldridge-Ferry plots and the Clausius-Clapeyron equation. The volume changes of gelation were estimated to be -25.7, -20.8 and -18.3 ml/mol of cross-links for gelatins of Bloom No. 60, 225 and 304, respectively, which were almost independent of pressure. The kinetic process of gelation was suppressed under high pressure, indicating the positive activation volume of gelation. These volume changes were discussed in terms of the characteristic hydration modes of cross-linking junctions of gelatin gels, comparing them with those of native collagen.