A new method for the determination of the concentration of free and associated sodium caseinate in model emulsions

摘要

This work shows a close correlation between density, sound velocity and X-ray scattering measurements at very small angles (SAXS) for solutions of industrial grade sodium caseinate (SC). As SAXS measurements at synchrotron radiation sources are not applicable on a laboratory scale every day we prove a close correlation between the structural data derived from scattering techniques with combined density and sound velocity measurements. As a new method for the determination of SC concentration we propose density measurements which require minimal sample preparation, have a short measuring cycle of just a few minutes, and yield very accurate, reproducible results, which allows sample reuse after the measurements. Linear density changes on the order of Δρ~(1 bar)_(20℃)= 0.0027 ± 0.0003 g cm~(-3) per weight percent of protein in the range of 0.99 ≤ ρ~(1 bar)_(20℃)≤1.04 g cm~(-3) are addressed. Such density dependence enables us to accurately determine the SC concentration in the continuous phase of model emulsions. The droplet mean size D of emulsion droplets is measured by laser light diffraction using the Mie theory coupled with polarization intensity differential scattering. To determine the SC concentration in the serum in equilibrium with the surrounding emulsion particles dispersed and continuous phase are separated using centrifugation at 2400g. Coupling of density measurement that provides the SC concentration in the aqueous phase and the mean droplet size measurement allows us to evaluate the surface density on emulsion globules, which is essential for emulsion studies.