Milk contains 3.2% protein (2.6% caseins and 0.6% whey). In addition to the caseins and whey proteins, milk contains protein nitrogen. Milk protein is a rich source of essential amino acids. Whey proteins are proteins that are passed along with the whey portion after the coagulation of milk. They contain 51% essential amino acids when compared to 45% in casein.
The caseins, which account for about 80% of the total milk proteins, exhibit strong interaction via hydrophobic, hydrogen, ionic, and calcium bonds. The caseins exist in milk as soluble complexes and as large, highly organized structures that contain colloidal milk salts, termed micelles.
Milk proteins have a high nutritional value compared to other proteins because of their relatively high content of essential amino acids and good digestibility. It was reported that the major milk proteins, including the caseins, ß-lactoglobulin and α-lactalbumin, are synthesized in the mammary epithelial cells and are only produced by the mammary gland.
The sulphur containing amino acids, which are considered essential and important, are found in higher concentration in whey protein than in casein. Usually, the quality of egg proteins is regarded as very high. But the net protein utilization, biological value and the protein efficiency ratio of milk protein come neck in neck with the quality of egg protein.
Lactalbumin, a whey protein, whose biological value, net protein utilization and protein efficiency ratio is considered superior when compared to the major milk protein, casein.
Normally, proteins of animal origin, such as milk (caseins and whey) are widely used in food formulation to improve the sensory characteristics.
Protein content in milk
