Chemistry of the Caseins

Milk protein is consumed widely as a human food, particularly in developed countries. The long history of its inclusion in the human diet and the relative ease with which the major proteins can be purified from raw milk have contributed to its early and extensive characterization by biochemists. Consequently, milk proteins are probably the best characterized of all food proteins; for example, the primary structures of all bovine milk proteins are known and even the three-dimensional structures of the major whey proteins are known. Nevertheless, the molecular characteristics, particularly the tertiary structure, of the caseins remain as a challenge since these proteins are not typical and apparently cannot be crystallized. In the past, the caseins have, at times, been inaccurately classified as denatured or random coil proteins. Although the caseins are apparently more flexible and less stable than typical globular or rod-shaped proteins, they appear to have some secondary structure and a definite unordered tertiary structure.