Natural State of Milk Proteins. I. Composition of the Micellar and Soluble Casein of Milk After Ultracentrifugal Sedimentation

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Abstract
Up to 99% of casein can be separated by ultracentrifugation from cow''s milk, if Ca is added in appropriate amounts and the pH maintained at 6.7. The gel-like casein sediment was quantitatively transformed to sodium caseinate by ion-exchange treatment, dialyzed and analyzed by electrophoresis. By this method the loss of proteins due to preparation is insignificant and the found casein composition can be considered as reliable for the natural complex of whole casein. If no Ca is added to milk, about 15% of the casein remains in solution after ultracentrifugation at 4[degree]C; at 20[degree]C the amount of soluble casein is about 5%. The P/N ratio of the soluble casein was found to be 0.045 (whole casein 0.055) and on electrophoresis the soluble casein showed a much higher percentage of beta and gamma casein compared to whole casein. The possible solubilizing effect of kappa casein is discussed.

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