Microstructure and rheology of phase-separated gels of gelatin + oxidized starch

We report on small-deformation rheology and confocal microscopy at 24 °C of high-sugar gel samples based on an aqueous mixture of gelatin + oxidized (non-gelling) starch exhibiting thermodynamic incompatibility. Using a standard protocol involving the heating of previously rapidly quenched samples at a fixed holding temperature (24–60 °C) for a fixed time (from 20 s to 30 min), gel samples of different storage modulus and degrees of spinodal-type phase separation were systematically generated. The developing time-dependent modulus of the gelatin gel was found to be sensitive to the extent of gelatin crosslinking as influenced by the nature of the thermal processing conditions. Under identical processing conditions, a gradual increase in starch content gave gels of lower elastic modulus and increased degree of microscopic phase separation. Taken all together, our results indicate that the gel rheology is determined by a subtle combination of overall system composition and temperature/time processing history. We conclude that the mechanical properties of this mixed biopolymer system are not directly deducible from the extent of phase separation observed microscopically without detailed additional information concerning sample preparation and treatment conditions.