Question

What proteins are in milk?

Answer 1

The total protein component of milk is composed of numerous specific proteins
There are two major categories of milk proteins that are broadly defined by their chemical composition and physical properties.

• The primary group of milk proteins are the $caseins$ and make up the largest structures in the fluid portion of the milk - the casein micelles. Each casein micelle is roughly spherical and about a tenth of a micrometer across. Caseins have an appropriate amino acid composition that is important for the growth and development of the nursing young. Collectively, they make up around 76% - 86% of the protein in milk by weight.
• Milk contains $dozens$ of other types of proteins besides caseins and including enzymes. These proteins are more water-soluble than caseins and do not form larger structures. These proteins remain suspended in whey, remaining when caseins coagulate into curds and are collectively called whey proteins.
• Other whey proteins are the $immunoglobulins$ (antibodies found in colostrum) and serum albumins - a serum protein. Whey proteins also include enzymes, hormones, growth factors, nutrient transporters, disease resistance factors, and others. Whey protein family consists of approximately 50% beta-lactoglobulins, 20% alpha-lactalbumin, lactoferrins, transferrins, and many minor proteins.