The interactions of high-methoxyl pectin (HMP) or soy soluble polysaccharide (SSPS) with caseins at low pH were studied in two model systems, acidified milk dispersions and sodium caseinate-emulsions. Above a critical concentration, both HMP and SSPS were able to stabilize casein particles at low pH. The stabilization of SSPS was pH-independent while HMP showed pH-dependency. At pH well above the isoelectric point of caseins, HMP and SSPS do not interact with caseins adsorbed at oil/water interface due to electrostatic repulsion. During acidification, acid-induced aggregation of emulsion droplets was prevented by the presence of sufficient HMP or SSPS. This is the first study showing the stabilization effect of SSPS on acidified caseinate-emulsion. The use of non-invasive techniques showed different dynamics of the interactions of HMP and SSPS with emulsions. This research contributes to a better understanding of their behaviour in dairy products, and may open novel applications, especially for SSPS.