Source and Components
Source
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]
Components
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
Casein contains various Bioactive peptides, which can be defined as sequences of amino acids that are contained in dietary proteins and are partially denatured in the stomach to reveal short sequences. These sequences can exert biological effects in the intestines prior to being digested, or may be digested through a peptide transporter.[14]
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
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]
