Molecular weight effects on the glass transition of gelatin/cosolute mixtures

Abstract

The structural properties of four gelatin fractions in mixture with sucrose and glucose syrup have been investigated extensively using small deformation dynamic oscillation. The total level of solids was 80%, the number average molecular weight of the protein ranged from 29.2 to 68 kD, and the temperatures were between 60 and -60 degrees C. Remarkably, the nature of the time and temperature dependence on the viscoelastic functions of all samples could be reduced to master curves using horizontal shift factors. The construction of master curves indicates a common mechanism of structure formation, which, in accordance with the synthetic polymer literature, comprises the rubbery zone, glass transition region, and glassy state. Application of Ferry's free-volume formalism and Rouse theory suggests that there is no change in the thermodynamic state of materials during vitrification, with changes in molecular weight simply introducing shifts in the time scale and temperature range of contributions to viscoelasticity. The thermorheological simplicity allowed development of the concept of "rheological" Tg. This was defined as the point between free-volume phenomena of the polymeric backbone occurring in the glass transition region and an energetic barrier to rotation required for local chain rearrangements in the glassy state. Mechanical relaxation and retardation distribution functions were calculated, thus obtaining values for the effective friction coefficient per monomer unit of the protein. It appears that the local friction coefficient is governed by a linear relationship between fractional free volume and the decreasing molecular weight of the protein, which introduces additional voids due to molecular ends.

Impact of the origin of gelatins on their intrinsic properties

“…The tendency of increment of viscosity and bloom strength within the same source of gelatin is in good agreement with literature (Kasapis, Al-Marhoobi, & Mitchell, 2003). However, these previous works did not use gelatins from different sources.…”

Solvent-induced lysozyme gels: Rheology, fractal analysis, and sol–gel kinetics

“…Some gelling processes, particularly those involving fibrous proteins, are induced by the effect of heating followed by cooling, leading to the entanglement of chains, such as in gelatin [1]. The effect of other species, such as sugar, on gelation in these instances is relevant and has been extensively studied [2].…”

Viscoelastic Properties of Membranes Measured by Spherical Indentation

“…8 The good agreement between bulk gel and membrane elastic properties found here is slightly surprising as gelation is not an instantaneous process; it has been observed that stiffening of gels may continue to occur for more than 6 h after gelation temperature is reached 24 and that the stiffness of the gel is also dependent on its temperature. 12 As membranes are very thin structures, they will desiccate much faster than a bulk gel of the same cross-sectional area due to a high surface area-to-volume ratio. Significant water loss coupled with rapid cooling may interfere with proper coil to helix transitions and thus generation of a highly interlinked solid matrix.…”