A rheo-optical methodology, based on small-angle light-scattering and transmitted-light-intensity measurements, has been used to perform an in situ and time-resolved investigation of the shear-induced mixing in ternary two-phase biopolymer emulsions. Aqueous emulsions on the basis of two proteins, two polysaccharides, protein and polysaccharide were chosen to elucidate the role of the solvent quality, composition of emulsion and phase viscosity ratio (PVR) on the phase behavior and emulsion morphology. The solvent quality has been quantified by determining the activity of the biopolymer in its saturated solution. It is shown that the level of activity of both biopolymers is a key factor in determining the capacity of the emulsion to undergo shear-induced mixing, while the interfacial tension and PVR of emulsions effect on the shear-induced phase behavior have a smaller effect. If the mean apparent activity of the biopolymer pair expressed as Log C-biopol is equal and higher than -0.15 a shear-induced mixing in biopolymer emulsions is observed at a very low shear rates (1 s(-1) and less). If the mean activity of the biopolymer pair is in the range from -0.4 to 0.9 a shear-induced mixing is registered at a higher shear rates (from 40 to 100s(-1) accordingly), while at a lower the mean activity, the phase transition is not observed at any shear rate studied (up to 200s(-1)). (C) 2008 Elsevier Ltd. All rights reserved.