Viscosity, size, structural and interfacial properties of sodium caseinate obtained from A2 milk

Abstract

Sodium caseinate (NaCN) obtained from A1A2 (regular) and A2 milks were compared for their viscosity, particle size and structure, and their absorption polystyrene particles surfaces. It was found that the viscosity as a function of concentration follows that of hard spheres dispersion, and is well described by the Quemada equation for concentrations up to 10 wt%, yielding a swelling ratio of Q=4.48 ± 0.01 mL/g. Dynamic light scattering measurements showed that the number and intensity average diameters were ∼10 and ∼68 nm, respectively. The difference is likely to be due to the presence of a few large NaCN particles. Small angle X-ray scattering showed that the radius of the particles was approximately ∼7 nm and that the NaCN internal structure was not homogeneous. NaCN formed a ∼10 nm protein layer at the surface of the latex particles with an estimated full surface coverage of 15.6 mg/m2. While these findings are within the values reported in the literature for NaCN solutions, this study showed that there is no obvious difference between the NaCN derived from A1A2 and A2 milks.