The effect of pressure on the structural properties of biopolymer/co-solute. Part II: The example of gelling polysaccharides

Abstract

The dependence of relaxation processes, as manifest in changes of the glass transition temperature, were examined under pressure (0.1-700 MPa) for the gelatin/co-solute system (part I of this series) and, currently, for preparations of agarose, κ-carrageenan and deacylated gellan in the presence of co-solute (part II). Structural properties were monitored using modulated differential scanning calorimetry and small-deformation dynamic spectroscopy on shear. Response curves as a function of hydrostatic pressure were treated with the combined framework of reduced variables and WLF equation/free volume theory. Shift factors derived from viscoelastic spectra and empirically treated thermograms clearly demonstrate that the effect of increasing pressure is detrimental to the stability of intermolecular polysaccharide associations. Diminishing values of the glass transition temperature with increasing pressure argue that the concept of time-temperature-pressure equivalence applicable to amorphous synthetic polymers is not operational in the structural functions of high-solid polysaccharide gels. © 2007 Elsevier Ltd. All rights reserved.