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Serum proteins or whey proteins remain soluble after adding rennet, or when the pH of milk is lowered to 4.6. They are found in whey hence their names: Soluble, serum, or whey proteins. They include β-lactoglobulin, α-lactalbumin, albumin serum and immunoglobulins. The β-lactoglobulin is quantitatively the most important serum protein.
Because of their high content of essential amino acids, such as lysine, methionine, and tryptophan, whey proteins have a nutritional value superior to casein and other food proteins.
Due to their more compact structure, whey proteins are more sensitive to heat than caseins. Thermal denaturation of the β-lactoglobulin associated with lactose degradation is responsible for the cooked taste that occurs in heated milk (Maillard reaction).
Once the milk is heated, the β-lactoglobulin can also form a complex with the κ casein at the surface of the micelles, and delay the coagulation of milk in cheese production.
The proteins exist in small quantities in the serum. In fact, they represent only about 13% of the dry matter of the serum. The extraction of these proteins is of great interest because they possess a high nutritional value, which is particularly appreciated in the dietary field. In addition, they possess excellent functional properties, which have a large number of specific roles in the texture of food preparation.