Structural Insights into the Bovine Casein Micelle: Small Angle X-Ray Scattering Studies and Correlations with Spectroscopy

¹ US Department of Agriculture, ARS, Eastern Regional Research Center, 600 East Mermaid Lane, Philadelphia, PA 19118

In the processing of milk into dairy products, the structure, stability, and dynamics of the casein micelle play definitive roles. These colloidal casein complexes are the result of an ensemble of multiple competing equilibria, arising from 1°, 2°, 3°, and 4° interactions of the individual caseins with themselves and with milk salts. Our laboratory has studied the fundamental principles of casein structure by application of modern methods of protein chemistry. The dynamics and quaternary structure of this interacting system have been examined using small-angle x-ray scattering. These data are now correlated with information obtained from [²H] nuclear magnetic resonance relaxation techniques, and with insights into the secondary structures of the caseins gained by Raman and Fourier-transform infrared spectroscopy. Results are interpreted in terms of a model where hydrophobically stabilized inhomogeneous submicelles are incorporated into the colloidal micelle while retaining most of their structural and dynamic properties.

Key Words: casein • small angle x-ray scattering • protein structure

Submitted on September 30, 1989
Accepted on March 23, 1990

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