title: Revisiting the interpretation of casein micelle SAXS data.
abstract: An in-depth, critical review of model-dependent fitting of small-angle X-ray scattering (SAXS) data of bovine skim milk has led us to develop a new mathematical model for interpreting these data. Calcium-edge resonant soft X-ray scattering data provides unequivocal evidence as to the shape and location of the scattering due to colloidal calcium phosphate, which is manifested as a correlation peak centred at q = 0.035 Å(-1). In SAXS data this feature is seldom seen, although most literature studies attribute another feature centred at q = 0.08-0.1 Å(-1) to CCP. This work shows that the major SAXS features are due to protein arrangements: the casein micelle itself; internal regions approximately 20 nm in size, separated by water channels; and protein structures which are inhomogeneous on a 1-3 nm length scale. The assignment of these features is consistent with their behaviour under various conditions, including hydration time after reconstitution, addition of EDTA (a Ca-chelating agent), addition of urea, and reduction of pH.
authors.affiliation: Callaghan Innovation, P.O. Box 31310, Lower Hutt 5040, New Zealand. bridget.ingham@callaghaninnovation.govt.nz.
authors.forename: B
authors.initials: B
authors.lastname: Ingham
authors.affiliation: School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
authors.forename: A
authors.initials: A
authors.lastname: Smialowska
authors.affiliation: School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
authors.forename: G D
authors.initials: GD
authors.lastname: Erlangga
authors.affiliation: School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
authors.forename: L
authors.initials: L
authors.lastname: Matia-Merino
authors.affiliation: Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3168, Australia.
authors.forename: N M
authors.initials: NM
authors.lastname: Kirby
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: C
authors.initials: C
authors.lastname: Wang
authors.affiliation: School of Engineering and Advanced Technology, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
authors.forename: R G
authors.initials: RG
authors.lastname: Haverkamp
authors.affiliation: School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand.
authors.forename: A J
authors.initials: AJ
authors.lastname: Carr