Particle-based stabilization of water-in-water emulsions containing mixed biopolymers

Abstract Background Structured food systems commonly contain mixtures of thermodynamically incompatible biopolymers located within a predominantly aqueous environment. The segregative phase separation of these mixed macromolecular systems at moderate polymer concentrations leads to the formation of so-called water-in-water (W/W) emulsions. Scope and approach For any set of aqueous solution conditions and polymeric components, the compositions of the coexisting phases within the equilibrium phase diagram are determined by a balance of molecular interactions as measured by experimentally accessible thermodynamic parameters. Compared with the fluid interface of a conventional oil/water dispersed system, the resulting water–water interface is characterized by a larger effective thickness and a lower interfacial tension. In consequence, the stabilization of a W/W emulsion system requires a different sort of emulsifying agent from that used in traditional emulsion technology. Key findings and conclusions Recent research has established that colloidal particles of various types are capable of accumulating at water–water interfaces. These include such entities as solid spherical particles (silica, polystyrene, protein), microorganisms, anisotropic clay particles, cellulose nanorods, deformable microgel particles, and protein-stabilized emulsion droplets. In principle, the protective effect of these particles against interfacial deformation and disruption is explicable using the same conceptual framework as applies to the more familiar Pickering-stabilized oil/water emulsions. Effective particle-based stabilization against coalescence and macroscopic phase separation of the W/W emulsion requires a state of close-packing and/or aggregation of colloidal particles at the water–water interface leading to a mechanically strong interfacial barrier around the dispersed water droplets.