Stability and the rheological properties of concentrated emulsions containing gelatin-κ-carrageenan polyelectrolyte complexes

We studied the influence of addition of polysaccharide (exemplified by kappa-carrageenan) to gelatin solution on the rheological properties, morphology, and stability of highly concentrated oil-in-water emulsions. Gelatin and kappa-carrageenan form polyelectrolyte complexes which stabilise emulsions. At some kappa-carrageenan/gelatin w/w ratios less than 0.7 (g(car)/g(gel)), these components form a stoichiometric complex which is in dynamic equilibrium when gelatin is in excess. At a kappa-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-kappa-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-kappa-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. (C) 2015 Elsevier B.V. All rights reserved.