Effects of urea addition on the structural and material properties of sodium caseinate solutions and emulsions

We investigate the effects of urea addition on the self-association properties of sodium caseinate in solution, its effects on solution viscosity at elevated protein concentrations, as well as on the stability and material properties of model sodium caseinate stabilised emulsion systems. Dynamic light scattering of 1 wt% sodium caseinate in solution showed a bimodal particle size distribution with peaks at ∼20 and 120 nm. The increasing addition of urea from 1.1 to 6.6 M was seen to cause a reduction in the peak area of the lower distribution, which has been attributed to a dissociation of the submicellar fraction due to a reduction in hydrophobic interactions. For sodium caseinate solutions above estimated submicellar close-packing phase volumes, addition of urea was seen to significantly lower solution viscosity. dium caseinate stabilised oil-in-water emulsions (30 vol%), addition of urea was seen to result in a reduction in depletion free energy of the emulsion. The effects of reduced depletion interaction on emulsion stability, structure and rheology were found to be dependent not only on the concentration of added urea, but also on the protein concentration in the emulsions.