Characterisation of sodium caseinate as a function of ionic strength, pH and temperature using static and dynamic light scattering

Extensive static and dynamic light scattering (DLS) measurements were done on sodium caseinate solutions as a function of the ionic strength (3–500 mM NaCl), pH (5–8) and temperature (10–70 °C). DLS results were analysed in terms of two populations: the caseinate and a small weight fraction of large particles with a hydrodynamic radius (Rh) of about 65 nm that was independent of the ionic strength, pH and temperature. Caseinate was present as individual molecules at low ionic strength (3 mM), but formed small aggregates (Rh=11 nm) at high ionic strength (>100 mM). The aggregation number (Nagg) increased weakly with decreasing pH between pH 8 and 6, but extensive acid-induced aggregation occurred below pH 5.4 at 250 mM and below pH 6.0 at 3 mM. Nagg increased reversibly with increasing temperature.