Abstract: A method for precipitating casein from a suspension comprising milk is disclosed. The method includes the following steps: adding a phosphate solution to a suspension; mixing the phosphate solution with the suspension to form a mixture having a phosphate concentration greater or equal to 40 mM; freezing the mixture having a phosphate concentration greater or equal to 40 mM to obtain a frozen mixture; and thawing the frozen mixture to obtain casein-containing aggregates in the mixture, in which the phosphate solution is buffered at a pH value of no less than 4.4.

Abstract: Methods for separating casein from soluble proteins in a composition. The method includes: adding a phosphate solution to the composition, mixing to form a mixture, freezing the mixture to obtain a frozen mixture, thawing the frozen mixture to obtain casein-containing aggregates in the mixture, and then centrifuging the mixture to obtain a supernatant traction and a casein-precipitate fraction. The supernatant fraction contains the soluble protein, which may be isolated by subjecting the supernatant fraction to a purification process. The method can be applied to purify a recombinant protein from the milk of a transgenic mammal.