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The influence of gelatin from bovine skin on the rheological properties of hydrogels in an extract from the alginate-containing algae Fucus vesiculosus was studied. The shear rate and dynamic mechanical analyses were used to determine the rheological properties. FT-IR spectroscopy showed that the main structural component of the Fucus extract was sodium alginate. The changes of the rheological properties of the extract with the introduction of gelatin are explained using the framework of the alginate–gelatin complexation model. The Fucus extract showed a weakly expressed non-Newtonian behaviour since the flow index in the Ostwald–De Waele equation is 0.91–0.94. The introduction of gelatin (1.0 wt.%) into the extract at 24 °C led to the formation of a hydrogel, whereas the extract itself cannot form a gel with these conditions. Further increasing the concentration of gelatin led to an exponential increase in the yield stress, plastic viscosity and apparent viscosity of the hydrogels. The introduction of gelatin into the Fucus extract at 4 °C led to a non-additive increase in the elastic modulus (G′), and a decrease in the tan δ of the hydrogels, i.e., strengthening of the elastic properties and weakening of viscous properties in these systems. The changes in the rheological parameters of a Fucus extract after the introduction of gelatin can be explained by an increase in the concentration of triple helices in the macromolecular chains of the gelatin, which are the elastic elements in the 3D mixed gel network.

Influence of the chitosan concentration in the low-concentrated acidic hydrogels formed by (bio)polyelectrolyte chitosan–gelatin complexes (at a constant gelatin concentration of 1%) was studied by shearing in steady flow and linear oscillations. These complexes, including native gelatin, demonstrate clearly expressed viscoelastic properties. Viscoelastic properties correlated well with the non-Newtonian behavior of hydrogels (according to the Cox–Merz rule). Increasing the chitosan concentration (from 0.1% to 0.6%) results in exponential growth of the apparent viscosity, yield stress, and storage modulus. However, a further increase in chitosan concentration to 0.8% leads to a reduction in these rheological parameters due to the electrostatic repulsion of similarly charged polyelectrolyte complexes under the high concentration of these complexes. The macro-rheological properties of chitosan–gelatin gels are mainly determined by the colloidal structure of sol-precursors in solutions. The yield str...

We studied the influence of addition of polysaccharide (exemplified by κ-carrageenan) to gelatin solution on the rheological properties, morphology, and stability of highly concentrated oil-in-water emulsions. Gelatin and κ-сarrageenan form polyelectrolyte complexes which stabilise emulsions. At some κ-carrageenan/gelatin w/w ratios less than 0.7 (gcar/ggel), these components form a stoichiometric complex which is in dynamic equilibrium when gelatin is in excess. At a κ-carrageenan/gelatin w/w ratio ≤0.1, the emulsions are stable against coalescence in the long-term but not against sedimentation. At ratios from 0.1 to 0.14, emulsions are stable against sedimentation. Highly concentrated emulsions at the dispersed phase content of 74–75% stabilised by gelatin–κ-carrageenan polyelectrolyte complexes are viscoplastic media (shear-unstable gels) and the clearly expressed yielding behaviour and the domain of the so-called “apparent” maximum Newtonian viscosity can be still detected. Solid-like behaviour of highly concentrated emulsions at low stresses is characterised by constant values of the storage modulus in a wide frequency range. The rheology of the emulsions under investigation depends on the ratio of components in the systems. An increase in the concentration of the gelatin–κ-carrageenan complexes (and consequently, the decrease in unbound gelatin) leads to a decrease in the emulsion viscosity, storage modulus, and yield stress with a tendency to disappear solid-like properties.