Substructure of bovine casein micelles by small-angle X-ray and neutron scattering

C. Holt, C.G. de Kruif, R. Tuinier, P.A. Timmins

Research output: Contribution to journalArticleAcademicpeer-review

151 Citations (Scopus)

Abstract

The casein micelles of cow's milk are polydisperse, more-or-less spherical, protein particles of up to several hundred nanometer in size, containing about 7% by dry weight of calcium phosphate. Small-angle neutron scattering with contrast variation and small-angle X-ray scattering were used in critical tests of models of casein micelle substructure. An inflexion in the neutron scattering curve near Q=0.35 nm-1 was observed in heavy water which became a more pronounced subsidiary maximum at the match point of the protein. In water-rich buffers, where the contrast between protein and calcium phosphate is small, the inflexion was less apparent. The position of the inflexion and its variation in shape and relative importance with contrast matching are explained poorly, if at all, by the submicelle models of casein micelle substructure. However, the observations are explained by a model in which a relatively uniform protein matrix contains a disordered array of calcium phosphate ion clusters. A notable achievement of the model is the prediction of the position of the subsidiary maximum from independent measurements of the intrinsic viscosity of micelles, their mass fraction of calcium phosphate and the mass of the core of a calcium phosphate nanocluster.

Original languageEnglish
Pages (from-to)275-284
Number of pages10
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume213
Issue number2-3
DOIs
Publication statusPublished - 12 Feb 2003
Externally publishedYes

Fingerprint

Casein
calcium phosphates
Calcium phosphate
Micelles
Neutron scattering
Caseins
substructures
X ray scattering
micelles
neutron scattering
proteins
Proteins
scattering
subsidiaries
x rays
Deuterium Oxide
Heavy water
milk
heavy water
Nanoclusters

Keywords

  • Calcium phosphate
  • Casein micelle
  • Small-angle
  • X-ray scattering

Cite this

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title = "Substructure of bovine casein micelles by small-angle X-ray and neutron scattering",
abstract = "The casein micelles of cow's milk are polydisperse, more-or-less spherical, protein particles of up to several hundred nanometer in size, containing about 7{\%} by dry weight of calcium phosphate. Small-angle neutron scattering with contrast variation and small-angle X-ray scattering were used in critical tests of models of casein micelle substructure. An inflexion in the neutron scattering curve near Q=0.35 nm-1 was observed in heavy water which became a more pronounced subsidiary maximum at the match point of the protein. In water-rich buffers, where the contrast between protein and calcium phosphate is small, the inflexion was less apparent. The position of the inflexion and its variation in shape and relative importance with contrast matching are explained poorly, if at all, by the submicelle models of casein micelle substructure. However, the observations are explained by a model in which a relatively uniform protein matrix contains a disordered array of calcium phosphate ion clusters. A notable achievement of the model is the prediction of the position of the subsidiary maximum from independent measurements of the intrinsic viscosity of micelles, their mass fraction of calcium phosphate and the mass of the core of a calcium phosphate nanocluster.",
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Substructure of bovine casein micelles by small-angle X-ray and neutron scattering. / Holt, C.; de Kruif, C.G.; Tuinier, R.; Timmins, P.A.

In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 213, No. 2-3, 12.02.2003, p. 275-284.

Research output: Contribution to journalArticleAcademicpeer-review

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AB - The casein micelles of cow's milk are polydisperse, more-or-less spherical, protein particles of up to several hundred nanometer in size, containing about 7% by dry weight of calcium phosphate. Small-angle neutron scattering with contrast variation and small-angle X-ray scattering were used in critical tests of models of casein micelle substructure. An inflexion in the neutron scattering curve near Q=0.35 nm-1 was observed in heavy water which became a more pronounced subsidiary maximum at the match point of the protein. In water-rich buffers, where the contrast between protein and calcium phosphate is small, the inflexion was less apparent. The position of the inflexion and its variation in shape and relative importance with contrast matching are explained poorly, if at all, by the submicelle models of casein micelle substructure. However, the observations are explained by a model in which a relatively uniform protein matrix contains a disordered array of calcium phosphate ion clusters. A notable achievement of the model is the prediction of the position of the subsidiary maximum from independent measurements of the intrinsic viscosity of micelles, their mass fraction of calcium phosphate and the mass of the core of a calcium phosphate nanocluster.

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