Rheological Study on Gelatin Gelation

Changes in the rheological properties of a gelatin solution during gelation were studied. Samples with various concentrations (0.1-6.0 wt%) were cooled from 45°C to 10 °C at a constant cooling rate and then kept at 10 °c. When the sample was cooled to a certain temperature, the viscosity started to increase. A steep rise in rigidity was observed after the viseosity increase. The vatlie of tanδ of each sampIe first increased and then decreased and converged to a characteristic vallie. We can understand this behaviour well in the framrwork of percolation transition theory. Concentration dependence of the rheological behaviour in the gelation process suggests that the gel structure of < 1.5 wt% samples and that of > 1.5wt% samples are different. In the higher concentration region, almost all the crosslinking points take part in the gel network formation, and thus the gels all feature an essentially similar structure. In the lower concentration region, some of the crosslinking points become dangling bOnds and do not contribute to rigidity, resulting in a mechanically weak gel network. A 0.1 wt%-order sample, that never gells macroscopically, also showed a rise in rigidity whell cooled, suggesting formation of a gel network of infinite size even in this low concentration range.