Proteins
Casein, lactalbumin, and lactoglobulin are the three proteins found in milk and are usually constant in a given species.
Casein is found nowhere in nature except in the secretion of the mammary glands. It is highly specialized and, as a nucleoalbumin, contains a certain amount of phosphorus. Lactalbumin is a protein found in quantities varying from 0.2% to 0.8%. It is similar to the serum albumin in blood and coagulates at 70° C. There is a mere trace of lactoglobulin in milk. It is insoluble in water.