All proteins are made up of a specific structure of amino acids, and the arrangement of these amino acids can greatly affect the biological properties of the protein. One family of proteins is caseins, which are present in the milk of all mammals. Casein is a significant protein source in many people's diets, though you can avoid if you are allergic by eliminating dairy products from your diet.
Dairy Products
Cow's milk is the major source of casein protein for many people. Cheese is also a significant source of casein protein, because the other main protein in milk, whey protein, is almost entirely removed during the cheese making process. Though most people only think of bovine milk when they think of casein protein, goat's milk and the milk from other mammals also contain casein. This means that cheese, yogurt and other dairy products from these animals have casein.
Casein Percentage
The amount of casein present in different types of milk can vary significantly. There are four different types of casein protein present in cow's milk, and they account for roughly 70 to 80 percent of the protein in the milk. Two different types of whey protein make up the remaining major proteins in cow's milk. Other mammals may have more or less casein in their milk. For example, goats have a similar amount of casein protein, but human milk only contains around 45 percent casein, at the most.
Protein Composition
Casein proteins contain all the essential amino acids, which are amino acids your body cannot create from other dietary nutrients. This makes casein a complete protein. Though all caseins are complete, they may not behave in the same way once you consume them in dairy products. For example, some people may be allergic to the casein protein present in bovine milk, but those same people can sometimes drink goat's milk without a reaction due structural differences in the casein proteins, even though the amino acid compositions are the same.
Digestibility
The casein protein you find in dairy foods is a slow-digesting protein. The structure of casein is such that it readily coagulates and gels in your stomach. The protein then can take seven hours or more to break down and release its amino acids into your body. The American Council on Exercise sports nutrition expert Fabio Comana states that the slow release of casein protein makes milk and other dairy products an excellent choice for athletes wanting a steady release of protein while they sleep, as it can prevent muscle tissue breakdown.
References
- "Strength and Conditioning Journal"; Protein Intake -- Effect of Timing; Jay R. Hoffman, Ph.D., FACSM, FNSCA
- American Council on Exercise: The Latest Scoop: Current Supplement Research Overview; Fabio Comana; 2010
- University of California: Dairy Goat Milk Composition; John C. Bruhn
- Food Standards Australia and New Zealand: A1 and A2 Milk; September 2007
- "American Journal of Clinical Nutrition"; Human-Milk Proteins - Analysis of Casein and Casein Subunits by Anion- Exchange Chromatography, Gel Electrophoresis, and Specific Staining Methods; C. Kunz and B. Lonnerdal; January 1990
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