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Definition of Casein | Fitness, Health & Exercise Glossary

Posted Feb 10 2009 11:00am

What is Casein? Learn the Definition of Casein Protein, Its Characteristics and Uses.

Definition of Casein

Casein (also known as “casein protein”) is a phosphoprotein found in cows milk and cheese. Casein is one of two primary proteins in dairy, the other being whey. Casein protein comprises approximately 80% of the protein in dairy and is the main protein in cheeses.

Casein coagulates in the presence of certain proteases, such as rennet and acids. In cheese making, protease enzymes in the form of rennet are added to milk, causing the casein proteins to separate from the liquid whey. The casein is then processed into cheeses.

In cottage cheese, the casein is left intact alongside the whey, which accounts for the lumpy texture. The curds are casein protein, and the liquid between the curds is the whey.

Because casein protein has limited secondary structure and a high proportion of proline peptides, it’s chemical bonds are not easily broken and it cannot be denatured. This means that the protein’s fundamental structure and natural characteristics remain intact even with heating or a change in pH. It is also poorly soluble in water.

Casein is used in a wide variety of applications, from cheese-making to industrial products like glue, to sports supplements.

Casein as a Protein Supplement

Because of its structure, casein behaves differently in the body when consumed. 

Unlike whey protein, which is quickly digested and utilized by the body, casein takes considerably longer to digest. When casein is ingested, it coagulates in the stomach and forms a gel, slowing digestion of the protein. Some research has shown that casein may take up to 7 hours to be fully digested.

The slow-digestion properties of casein have made it a popular sports and fitness supplement.

Supplement manufacturers take casein, filter it and then dry the protein, making a powder that is a stable, portable and highly-concentrated form of slow-digesting protein.  There are three primary forms of casein protein available: calcium caseinate (which is primarily used as a food additive), micellar casein, and milk protein isolate.

Micellar casein is a more purified form of casein and will typically not contain whey. Milk protein isolate, however, will contain some whey alongside the casein. The typical protein profile of most milk protein isolate products is approximately 80 percent casein protein to 20 percent whey by volume.

Casein and Sports Nutrition

Casein is frequently used by athletes and bodybuilders as a source of slow-digesting protein.

This slow-release of amino acids over a period of several hours may have an anti-catabolic effect in the body, maintaining positive nitrogen balance and discouraging muscle breakdown. For this reason, athletes will often consume casein protein before bedtime in order to blunt catabolism during sleep.

Clinical research has also indicated that combining casein protein with whey as part of a post-workout recovery drink may encourage increases in lean mass over individuals who consume a whey-only drink; a carbohydrate recovery drink or a whey-carb combination. The hypothesis is the whey protein supports short-term protein synthesis and recovery, while the slower-digesting casein protein has anti-catabolic effects.

Whole Food Sources of Casein

While casein supplements provide low-fat, portable sources of concentrated casein protein, casein is also available in whole food sources of dairy, such as skim milk or low-fat cottage cheese or yogurt.

Casein makes up 80 percent of the protein in milk, so an eight ounce serving of skim milk will provide a little over 7 grams of casein protein.  A one cup serving of low-fat cottage cheese will contain approximately 22 grams of casein, putting it just about on par with a scoop of casein protein powder.

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