Thermal treatment of electrostatic complexes, above the denaturation temperature of the protein, is one possible method to induce particle formation and improve their stability towards changes in environmental conditions. The purpose of this study was to examine the effect of thermal treatment on mixtures of commercial, food-grade potato protein (PP) and anionic polysaccharides. Mixed solutions (1 wt%) of PP and gum arabic (GA) or carboxymethylcellulose (CMC) were acidified (pH 9.5 to 3.5), homogenized (200/50 bar) and pasteurized (90 degrees C, 10 min). The physicochemical properties of the acidified and heated samples were compared on particle size, charge, composition, turbidity and stability. It was found that the acidification in itself initiated formation of PP-GA and PP-CMC microparticles (MP). Upon heating, PP-GA MPs became smaller (d(4,3) from 2.5 to 1.3 mu m), uniformer, and the amount of PP incorporated was increased with 33%, causing more than a doubling of the turbidity. Oppositely, PP-CMC MPs did not change upon heating; the particles remained small (d(4,3) 0.8 mu m) and polydisperse, consisting of 2.5:1 PP:CMC. It was hypothesized that the heat resistance of PP-CMC MPs was caused by stronger electrostatic forces between PP and CMC, while the heat-induced salt and pH resistance of PP-GA particles indicated the formation of other types of interactions preserving the MPs. Negative zeta potentials suggested PS was present at the exterior of the MPs. The obtained results demonstrated PP's ability to create micron-sized particles with polysaccharides, which could potentially replace dairy proteins in various applications.