Effect of Calcium Concentration on the Structure of Casein Micelles in Thin Films

• Published in: Biophysical journal Vol. 93; no. 3; pp. 960 - 968
• Main Authors: Müller-Buschbaum, P., Gebhardt, R., Roth, S.V., Metwalli, E., Doster, W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2007; Biophysical Society; The Biophysical Society
• Subjects: Aggregates; Animals; Biochemistry; Calcium; Calcium - chemistry; Calcium - pharmacology; Caseins - chemistry; Caseins - drug effects; Caseins - isolation & purification; Caseins - ultrastructure; Light; Micelles; Microscopy; Microscopy, Atomic Force; Milk; Milk - chemistry; Molecular biology; Protein Binding; Scattering, Radiation; Solutions; Supramolecular Assemblies; Thin films; Ultrafiltration; X-Ray Diffraction
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.107.106385

The structure of thin casein films prepared with spin-coating is investigated as a function of the calcium concentration. Grazing incidence small-angle x-ray scattering and atomic force microscopy are used to probe the micelle structure. For comparison, the corresponding casein solutions are investigated with dynamic light-scattering experiments. In the thin films with added calcium three types of casein structures, aggregates, micelles, and mini-micelles, are observed in coexistence with atomic force microscopy and grazing incidence small-angle x-ray scattering. With increasing calcium concentration, the size of the aggregates strongly increases, while the size of micelles slightly decreases and the size of the mini-micelles increases. This effect is explained in the framework of the particle-stabilizing properties of the hairy layer of κ-casein surrounding the casein micelles.