Milk is a complete food as it comprises of vital nutrients and proteins.
Major proteins in Milk
Casein and whey protein are the major proteins of milk. Casein constitutes approximately 80%(29.5 g/L) of the total protein in bovine milk, and whey protein accounts for about 20% (6.3 g/L). The nitrogen content of milk is distributed among caseins (75%), whey proteins (18%), miscellaneous proteins (2%) and non-protein nitrogen (5%).
The protein present in milk is due to the primary, secondary and tertiary structures.
- The primary structure of proteins consists of a polypeptide chain of amino acids residues joined together by peptide linkages, which may also be cross-linked by disulphide bridges.
- The secondary structure applies to the spatial arrangement of amino acid residues that are near one another in the linear sequence.
- The tertiary structure implies to the spatial arrangement of amino acid residues that are far apart in the linear sequence, giving rise to further coiling and folding.
If the protein is tightly coiled and folded into a somewhat spherical shape, it is known as globular protein. If the protein comprises of long polypeptide chains that are intermolecularly linked, they are called fibrous proteins. Quaternary structure occurs when proteins with two or more polypeptide chain subunits are associated.