Rheological and Differential Scanning Calorimetric Study of Sol-to-Gel Transition of Gelatin

Abstract

Gelation process during cooling a gelatin sol was studied with a vibrating rod rheometer and a differential scanning calorimeter (DSC). As temperature decreased, rise in the viscosity was observed first, and then rise in the rigidity followed. This behavior did not depend on experimental conditions, such as sample gelatin examined, sample concentration, cooling rate. The rise in the viscosity corresponds to the start of the intermolecular crosslinkage, and the rise in the rigidity the divergence of the gel network size through 'percolation transition'. DSC measurement under the identical conditions to the rheological measurements gave an exothermic peak. The onset temperature of the DSC peak approximately agrees with the temperature where the viscosity starts to increase. As the heat generation in gelation corresponds to the formation of hydrogen bonding, that is, crosslinkage, the above behavior is reasonable. The concentration dependence of gelation examined with rheological measurements shows that the gelation temperature steeply decreases when the concentration is lower than ca. 2 wt% presumably caused by the formation of intramolecular hydrogen bonds. The change in gel structure in this region was suggested.