Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) study on the structure of sodium caseinate in dispersions and at the oil-water interface: effect of calcium ions

The structure of sodium caseinate particles, as affected by the presence of calcium ions (Ca2+), in aqueous solution and in oil (toluene)-in-water emulsions, was investigated by small-angle X-ray and neutron scattering (SAXS and SANS). SAXS analyses indicated that the sodium caseinate dispersed in water as small particles with electrostatic interactions, which has a radius of gyration (Rg) of ~5 nm and an effective radius (Reff) of ~ 10 nm with an assuming spherical shape. In the presence of Ca2+, the caseinate particles aggregated as large particles with a hydrodynamic diameter > 100 nm as determined by dynamic light scattering. The networks within the large particles were self-assembled from the small Ca2+-cross-linked particles (Rg ~ 6.5–8.0 nm), as probed by SAXS. The fractal-like dimension increased from 2.5 to 3.4 with increasing protein and CaCl2 concentrations, suggesting a denser structure. The integrity of the caseinate particles at the oil-water interface was enhanced by Ca2+ cross-linking, as observed by transmission electron microscopy. The oilsingle bondwater interface stabilised by Ca2+-cross-linked caseinate particles was ~ 30 nm thick, six times thicker than that stabilised by sodium caseinate (~ 5 nm) as analysed by SANS with contrast variation technique. Quantifying the structure of sodium caseinate in an aqueous solution and at the oil-water interface provides valuable insights for designing new casein-based functional materials. © 2022 Elsevier Ltd

Keywords

Small angle scattering, Sodium, Emulsions, Dispersions, Water, Particles, Interactions, Aqueous solutions, Neutron diffraction

Citation

Cheng, L., Ye, A., Yang, Z., Gilbert, E. P., Knott, R., de Campo, L., Storer, B., Hemar, Y., & Singh, H. (2022). Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) study on the structure of sodium caseinate in dispersions and at the oil-water interface: effect of calcium ions. Food Structure, 32, 100276. doi:10.1016/j.foostr.2022.100276