Last Updated: September 28 2022

Cow milk protein is 80% casein and 20% whey protein. In your stomach, casein forms a gel and thus digests slowly. The protein in cheese is mostly casein.

Casein is most often used for

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Source and Components



Casein is a protein that is derived from the milk of many species; most human consumption of casein comes from bovine (cow) milk.

Casein is the insoluble portion of the milk, whereas whey is the soluble portion; the amount of casein in standard milk protein is approximately 80%, and human milk is variable depending on time spent lactating.[1][2][3][4]



Casein protein, like all protein, is a source of dietary amino acids. As it is an animal source, it is complete in the sense that it contains all essential amino acids in adequate enough numbers for proper human functioning at the minimum level of protein intake recommended.

Casein protein also contains various bioactive peptides. These peptides are partially digested in the stomach, and prior to being broken down into their constituent amino acids they are able to exert effects in the intestines (prior to absorption). These effects may be wide-reaching, and are discussed in the following bullets.


Production of Casein


Standard Processing

Standard processing of casein involves a separation of the two dairy proteins (casein and whey).

Whole milk protein is treated with a compound known as a 'coagulant', usually chymosin[5], which serves to coagulate (congeal, or solidify) the casein fragment. This is a step crucial to cheese making (which requires casein to provide a solid foundation) but is also significant for separating the wheys and casein (curds).[6][7]

With the casein fragment more solid, the whey fragment (still liquid) is then separated from the casein through a process called syneresis. The degree of syneresis varies depending on what the end product (usually cheese) would be, and can be manipulated by salt[8], acidity[9], enzyme treatment[10] and physical disturbances[11] amongst other techniques to provide unique flavor and texture to the end product cheese. Casein protein supplementation is more concerned with the extraction of as much whey as possible, which leaves pure casein protein behind.


Micellar Casein

Micellar casein tends to be produced via microfiltration, which has the ability to concentrate the micellar segments of casein.[12][13]


List of Peptides in Casein


AlphaS-1 Peptide

When supplemented to women at 150mg daily, the AlphaS-1 peptide is known to produce an anxiolytic effect.[15] Two doses of 200mg may be able to reduce the response to perceived stressors.[16] The anxiolytic effect may also provide better sleep in those with high levels of stress.[17]

Similar to the c12 peptide, AlphaS-1 may also have an ability to induce ACE-inhibitor like effects and reduce blood pressure.[18]

AlphaS-1 is also a peptide that is noted to cause allergies, and thus persons allergic to dairy may also be allergic to this peptide in supplemental form.[19]


c12 Peptide

When administered in the form of tablets, the c12 peptide at a dose of 3.8g daily for 4 weeks is able to reduce blood pressure in pre-hypertensive subjects from an average of 138/87 to 127/80 in one study.[20] This is due to the c12 peptide having the properties of an ACE inhibitor.[21]



Glycomacropeptides can be found in the casein portion of whole milk products, but due to their water soluble nature they leave the casein portion during chymosin treatment at the beginning stages of processing.[22] They do tend to be associated with casein protein as they originate with kappa casein molecules, hence their inclusion in this Examine page. Unless otherwise added afterwards however, they are not a normal component of casein supplementations.


Caseinophosphopeptides (CPPs)


Casoxins and Casomorphins

Casoxins and Casomorphins are peptides which are able to act on the opioid system, which is involved in the rate of digestion. The class of casomorphins are opioid agonists (activators) and the casoxins opioid antagonists.[23]

Casein seems to have a higher relative content of casomorphins to casoxins, which may explain the reduced transit speed after consumption (as activation of the opioid system reduces intestinal motility).[24]


Casein Hydrolysate (Hydrolyzed Casein)


Digestion Speed


Effects on protein synthesis


Neurological Effects

It has been shown to have a more relaxing effect at rest and after mental stress when compared to maltitol,[25] which may be related to a specific tryptic hydrolysate found in bovine casein.[26] This AlphaS1 peptide has been shown to reduce stress when ingested by women at 150mg daily.[15]

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2.^Lönnerdal B, Forsum ECasein content of human milkAm J Clin Nutr.(1985 Jan)
3.^Kunz C, Lönnerdal BRe-evaluation of the whey protein/casein ratio of human milkActa Paediatr.(1992 Feb)
4.^Belloque J, Ramos MDetermination of the casein content in bovine milk by 31P-NMRJ Dairy Res.(2002 Aug)
5.^Kumar A, Grover S, Sharma J, Batish VKChymosin and other milk coagulants: sources and biotechnological interventionsCrit Rev Biotechnol.(2010 Dec)
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15.^Kim JH, Desor D, Kim YT, Yoon WJ, Kim KS, Jun JS, Pyun KH, Shim IEfficacy of alphas1-casein hydrolysate on stress-related symptoms in womenEur J Clin Nutr.(2007 Apr)
17.^Guesdon B, Messaoudi M, Lefranc-Millot C, Fromentin G, Tomé D, Even PCA tryptic hydrolysate from bovine milk alphaS1-casein improves sleep in rats subjected to chronic mild stressPeptides.(2006 Jun)
18.^Rousseau-Ralliard D, Goirand F, Tardivel S, Lucas A, Algaron F, Mollé D, Robert V, Auchère D, Boudier JF, Gaillard JL, Monnet V, Tauzin J, Grynberg AInhibitory effect of αS1- and αS2-casein hydrolysates on angiotensin I-converting enzyme in human endothelial cells in vitro, rat aortic tissue ex vivo, and renovascular hypertensive rats in vivoJ Dairy Sci.(2010 Jul)
19.^Schulmeister U, Hochwallner H, Swoboda I, Focke-Tejkl M, Geller B, Nystrand M, Härlin A, Thalhamer J, Scheiblhofer S, Keller W, Niggemann B, Quirce S, Ebner C, Mari A, Pauli G, Herz U, Valenta R, Spitzauer SCloning, expression, and mapping of allergenic determinants of alphaS1-casein, a major cow's milk allergenJ Immunol.(2009 Jun 1)
20.^Cadée JA, Chang CY, Chen CW, Huang CN, Chen SL, Wang CKBovine casein hydrolysate (c12 Peptide) reduces blood pressure in prehypertensive subjectsAm J Hypertens.(2007 Jan)
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26.^Messaoudi M, Lalonde R, Schroeder H, Desor DAnxiolytic-like effects and safety profile of a tryptic hydrolysate from bovine alpha s1-casein in ratsFundam Clin Pharmacol.(2009 Jun)