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

Abstract

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.