Methods for separating casein from soluble proteins in a composition

A method for separating casein from a soluble protein in a composition comprising milk, comprising:

• adding a phosphate solution to a composition;
• mixing the phosphate solution and the composition 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;
• thawing the frozen mixture to obtain casein-containing aggregates in the mixture;
• and
• centrifuging the mixture to obtain a supernatant fraction and a casein-precipitate fraction, in which the supernatant fraction comprises the soluble protein;
• wherein the phosphate solution is buffered at a pH value of no less than 4.4.

A method for isolating a recombinant protein from the milk of a transgenic mammal, comprising:

• adding a phosphate solution to the milk;
• mixing the phosphate solution and the milk to form a mixture;
• freezing the mixture to obtain a frozen mixture;
• thawing the frozen mixture to obtain casein-containing aggregates in the mixture;
• centrifuging the mixture containing casein aggregates to obtain a supernatant fraction and a casein-precipitate fraction, in which the supernatant fraction comprises the recombinant protein;
• removing the supernatant fraction;
• and
• purifying the recombinant protein from the supernatant fraction to obtain the recombinant protein;
• wherein the phosphate solution is buffered at a pH value of no less than 4.4.