Further observations on the size, shape, and hydration of casein micelles from novel analytical ultracentrifuge and capillary viscometry approaches

The size, shape, and hydration of casein micelles were estimated using a combination of sedimentation velocity (time-derivative analysis) in the analytical ultracentrifuge and capillary viscometry applied to skimmed milk. On the basis of sedimentation time-derivative and Wales-van Holde analyses the casein micelles appear as large spherical molecules of s⁰ _T,b = 845S, M_w ∼ 2.8 × 10⁸, hydrodynamic radius ∼77.8 nm, and k_s/[η] = 1.6. The molecular hydration (i.e., the extent of chemically bound and physically entrained solvent) was calculated to be 3.4 g/g. These results appear to be in good agreement with comparable results from electron microscopy and dynamic light scattering.