High-Pressure Effects on Gelatin Sol-Gel Transition

We investigated the effects of high hydrostatic pressure on the sol-gel transition of gelatin dispersions. We used dynamic light scattering (DLS) and DLS-based passive microrheology to monitor the evolution of the viscoelasticity during isothermal gelation. It provided easy identification of the sol-gel transition and the isothermal critical gelation time (t _c) and values of viscosities of sols and shear modulus of gels. At a given temperature, t _c decreased with increasing pressure. Up to 100 MPa, the temperature dependence of t _c followed the established empirical rule and the critical temperature T _c increased with pressure by ∼0.04 K/MPa. The critical gelation time scaled with the quench depth T-T _c or equivalently with the distance from the pressure-dependent collagen denaturation temperature (∼314 K, at 0.1 MPa), which also increases by ∼0.04 K/MPa in the first 100 MPa. The pressure dependence also reflected on the time evolution of the intrinsic viscosity, η , or elastic modulus, G _p, in the sol or gel state, respectively, are reported. Both η or G _P evolution speeds up with pressure. Finally, using a reverse quenching approach, we observed a slowing of the gel melting when the pressure increases. Our results confirmed that the rheological evolution reflects the helix formation process and that pressure stabilizes the helices.