Proteins in Milk: Properties and Separation

Study Notes

Milk proteins are amphoteric, reacting with both acids and bases due to having amino and carboxyl groups in their chemical structure.

Casein is the main protein of milk, making up approximately 80% of total milk proteins.
Casein coagulates or precipitates at pH 4.6, which is the principle behind cheese curd formation.
The casein family consists of several types, including α-s1, α-s2, β, and κ, each with unique properties and functions.
Casein is suspended in milk as a complex called a micelle, which can associate with calcium to form calcium phosphate salts.
α-s Casein is sensitive to calcium ions, while κ-Casein is insensitive and stabilizes the casein micelle structure.

Whey proteins make up around 20% of total milk proteins and do not contain phosphorus.
Whey proteins remain in solution in milk at pH 4.6 and include proteins such as β-lactoglobulin, α-lactalbumin, blood serum albumin, immunoglobulins, and minor proteins.
β-Lactoglobulin is thought to be a carrier of vitamin A, while α-lactalbumin plays a critical role in lactose synthesis.

Casein is heat-stable, surviving pasteurization at temperatures around 62-71°C, unlike whey proteins, which are denatured at these temperatures.
Casein solubility is pH-dependent.

Casein is used in the plastics industry, in the manufacture of book covers and magazines, and in the textile and paint industries.

The size of fat globules in milk depends on factors such as animal type, breed, and nutrition.
Milk fat globules are surrounded by a thin membrane composed primarily of lipids and proteins, which protects them from lipase enzyme action.

Phospholipids play an essential role in nutrition, particularly in bone building and brain cell development.
Phospholipids act as emulsifying agents and stabilize foam, making them crucial in the manufacture of products like ice cream.

Amino acids combine chemically to form protein molecules with high molecular weight through peptide bonds.
The peptide bond is formed by the combination of a carboxylic group of one amino acid with the amino group of another.

Amino acids contain acidic and basic groups, allowing them to interact with acids and alkalis.
In alkaline media, amino acids carry negative charges, while in acidic media, they carry positive charges.