Cheese making, protein precipitation

Cheese Whey Protein Recovery. Perhaps the best publicized application for UF is in cheese whey processing. "Cheese whey" is the supernatant liquid produced in the cheese making process after precipitation of casein from milk. There are two types of whey "sweet" whey (minimum pH of 5.6) results when rennet-type enzymes are used to coagulate the casein to form Gouda and Cheddar cheeses ... 

It is one of the proteins of milk, sometimes called a whey protein. During the making of cheese, lactalbumin is not precipitated with the protein casein and thus, it appears in the whey. One half, or more, of the protein in human milk is lactalbumin the rest is casein. 

The isoionic point of a protein depends upon its amino acid composition. At its isoionic point, a protein has no net charge, and its solubility is at a minimum. As a consequence, a protein tends to precipitate form solution at its isoionic point. For example, casein, a protein in milk, has a negative charge at pH 6.3. Casein has many glutamic acid and aspartic acid residues. If acid is added to milk, these side chains are protonated, and casein precipitates. Casein is used in making cheese, and it is obtained by adding acid to milk or by adding bacteria that make lactic acid, which has the same effect. 

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