Milk and cheese are rich sources of protein, an essential nutrient that humans need to carry out most of the functions of the body. The exact degree to which each type of protein exists in milk may change depending upon time of lactation and the diet of the animal that produced it, but the composition remains fairly constant.
Protein is essential to the functions of the body. According to experts at Columbia University, it facilitates chemical reactions, transports molecules like oxygen through the body, contracts the muscles, creates antibodies to fight off infections and regulates the metabolism. Adults need 0.8 g/kg of body weight to replace the amount of protein lost every day through excretion.
A single cup of milk, whether whole, reduced fat or skim, contains approximately 8 g of protein, which constitutes about 3.3 percent of its contents. The amount of protein in cheese depends upon the type. For example, 1 oz. of part skim mozzarella contains 7.79 g of protein; whole milk mozzarella has 5.51 g. Other cheese have the following amounts of protein: 7.06 g in cheddar, 6.64 g in Muenster, 6.28 g in American cheese, 6.07 in blue, 4.03 g in feta and 2.82 g in French Neufchâtel.
Proteins are constructed from building blocks called amino acids. Of the 22 amino acids, 20 are regular amino acids and two are incorporated to "stop" the cell from reading the genetic code that transcribes the protein. The nine amino acids that cannot be synthesized by the human body and must be obtained from the diet are known as essential amino acids. Milk and milk products contain all nine essential amino acids required by humans.
Two main types of milk protein exist. Casein makes up approximately 82 percent of the protein in milk. The casein contains phosphorous and thus will coagulate at a certain acidity level, which is the basis for curd formation, which are the solid parts of cottage cheese. Whey constitutes the remaining 18 percent. It does not contain phosphorous and will not coagulate. Both casein and whey can be broken down into even smaller constituent parts such as globulins. The percentage to which they are present in milk depends upon the state of the animal during lactation. Although both proteins have nutritional value, casein is more universally useful to your cells because of its phosphorus component.
The University of Minnesota Department of Animal Science reports that only 94 percent of the total protein in milk is true protein. The other 6 percent is non-protein nitrogen compounds such as milk urea, an organic compound that serves an important role in the metabolism of other nitrogen-containing molecules that exist in living organisms.