We report confocal microscopy observations of the spatial distribution of monodisperse charge-stabilized colloidal particles (amphoteric polystyrene latex) incorporated within a spinodal-type phase-separating system of mixed biopolymers (gelatin + oxidized starch). Images from samples aged at 40 degrees C demonstrate a strong tendency for the added particles to accumulate at the liquid-liquid interface and to influence the rate of coarsening of the complex bicontinuous microstructure. Large variations in the local curvature of particle-rich inter-facial regions are suggestive of a liquid-liquid boundary that is substantially viscoelastic.