Question

What proteins are present in milk?

Answer 1

Milk is a nutrient-rich liquid food produced by mammals' mammary glands. It is the primary source of nutrition for young mammals, including breastfed human infants, before they can digest solid food.

Complete answer:
Milk's main proteins are casein and whey protein. In bovine milk, casein accounts for around $80\%$ (29.5 g/L) of the total protein, while whey protein accounts for about $20\%$ (6.3 g/L). Caseins (75 percent), whey proteins (18 percent), miscellaneous proteins (2 percent), and non-protein nitrogen make up milk's nitrogen composition (5 percent ).
Structure
Milk protein is made up of primary, secondary, and tertiary structures.
Proteins have a polypeptide chain of amino acid residues linked together by peptide linkages, which can also be cross-linked by disulphide bridges.
A protein is called globular if it is tightly coiled and folded into a somewhat spherical shape. Fibrous proteins are those that are made up of long polypeptide chains that are intermolecularly linked. When proteins with two or more polypeptide chain subunits are linked together, they form a quaternary structure.
The secondary structure refers to the spatial arrangement of amino acid residues in the linear sequence that are close to one another.
The tertiary structure denotes the spatial arrangement of amino acid residues that are far apart in the linear sequence, resulting in additional coiling and folding.

Note:
Colostrum is early-lactation milk that contains antibodies that strengthen the immune system and thus reduce the risk of many diseases. It contains a variety of other nutrients, including protein and lactose. Milk consumption between species is not uncommon, especially among humans, many of whom consume the milk of other mammals