The effect of pressure on the glass transition of biopolymer/co-solute. Part I: The example of gelatin

Abstract

High-solid materials of gelatin in the presence of co-solute were prepared and subjected to a series of hydrostatic pressures up to 700 MPa. Following this, a study was made of the relaxation properties of the mixture around the glass transition region and the melting behaviour of the gelatin network. Structural properties were monitored using differential scanning calorimetry and small-deformation dynamic oscillation on shear. Thermograms were obtained and master curves of viscoelasticity were constructed for each experimental pressure. The dependence of the empirical shift distances obtained from mechanical measurements and supplementing evidence from thermal analysis argue that the application of pressure did not alter the vitrification or melting characteristics of the gelatin/co-solute system within the experimentally accessible pressure range. Unlike the principle of the time-temperature-pressure superposition applicable to synthetic macromolecules, it may not be possible to incorporate a pressure component into the framework of thermorheological simplicity governing the glass transition of the high-sugar gelatin network. © 2006 Elsevier B.V. All rights reserved.