We examine the issue of whether a low-volume fraction of nano-and microparticles can lead to phase separation in semidilute biopolymer mixtures. To this end, we determine the phase diagrams and ESEM images of aqueous semidilute and weakly structured sodium caseinate-sodium alginate-dextran sulfate (SC-SA-DS) systems in the presence of several charged micro particles with a diameter less, higher, and comparable with the size of the system network holes (2-3 mm). We demonstrate that 3 mu m particles (both negatively and positively charged) help to enhance phase separation, and increase the viscoelastic properties of the emulsion, whereas the larger particles affect oppositely, and nanoparticles (210 nm and 910 nm in diameter) do not affect appreciably the phase separation and rheology. Experimental observations suggest that the dominant mechanism responsible for the decreased thermodynamic compatibility in such systems may be the formation of the large charged microparticle (3 mu m)-SC/DSS associates in SC enriched phase that leads to decrease their compatibility with alginate due to the effect of the excluded volume interactions between SA and microparticle-DS + SC associates. Decrease in compatibility and increase in viscoelastisity are more pronounced by using highly charged hydrophobic carboxylate modified sulfonate latex (CLM sulfonate) and sulfate latex, and, to a lesser estend by use of aliphatic amino latex, and hydrophilic CLM latex.