Speaker: Bridget Ingham, Callaghan Innovation (Wellington, New Zealand)
Program Description
Most of the dietary calcium in milk is contained within casein micelles as so-called ‘colloidal calcium phosphate’ (CCP) nanoclusters around 2-3 nm in size. Various casein micelle models have been proposed, including the submicelle, nano-cluster, dual-binding and interlocking lattice models. Small-angle X-ray and neutron scattering (SAXS and SANS) have been used for several decades to study the internal structure of bovine casein micelles, but there is lingering controversy over the interpretation of the scattering data.
To resolve this, we conducted resonant soft X-ray scattering of bovine milk at the Ca L2,3-edges using beamline 11.0.1.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory. This technique utilizes the wavelength tuneability of synchrotron radiation to obtain element-specific information about the scattering objects that are present. We observed a prominent resonant feature at the Ca L2,3 edges. In contrast, no significant differences were observed in the scattering feature commonly attributed to CCP, supporting a hypothesis that this feature is primarily due to protein inhomogeneities within the casein micelle.
In addition, we have conducted a number of anomalous SAXS measurements and time-resolved SAXS experiments in the hard X-ray region using the SAXS/WAXS beamline at the Australian Synchrotron. The anomalous SAXS experiments were performed on iron-fortified milk at the Fe K-edge and show intensity differences in the same region of the SAXS pattern as the Ca-resonant feature. The time-resolved measurements shed additional light on the internal micelle structure through an understanding of the chemical changes that occur.
B. Ingham et al., Soft Matter 11 (2015) 2723-2725.
