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

Abstract

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 ( R h) 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 ( R h=11 nm) at high ionic strength (>100 mM). The aggregation number ( N agg) 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. N agg increased reversibly with increasing temperature.