Casein (// or //, from Latin caseus, "cheese") is the name for a family of related phosphoproteins (αS1, αS2, β, κ). These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 20% and 45% of the proteins in human milk. Casein has a wide variety of uses, from being a major component of cheese, to use as a food additive, to a binder for safety matches. As a food source, casein supplies amino acids, carbohydrates, and the two inorganic elements calcium and phosphorus.
- 1 Composition
- 2 Beta-casein
- 3 Uses
- 4 Controversies
- 5 See also
- 6 References
- 7 Further reading
- 8 External links
Casein contains a fairly high number of proline residues, which do not interact. There are also no disulfide bridges. As a result, it has relatively little tertiary structure. It is relatively hydrophobic, making it poorly soluble in water. It is found in milk as a suspension of particles called "casein micelles" which show only limited resemblance with surfactant-type micellae in a sense that the hydrophilic parts reside at the surface and they are spherical. However, in sharp contrast to surfactant micelles, the interior of a casein micelle is highly hydrated. The caseins in the micelles are held together by calcium ions and hydrophobic interactions. Any of several molecular models could account for the special conformation of casein in the micelles. One of them proposes the micellar nucleus is formed by several submicelles, the periphery consisting of microvellosities of κ-casein. Another model suggests the nucleus is formed by casein-interlinked fibrils. Finally, the most recent model proposes a double link among the caseins for gelling to take place. All three models consider micelles as colloidal particles formed by casein aggregates wrapped up in soluble κ-casein molecules.
The isoelectric point of casein is 4.6. Since milk's pH is 6.6, casein has a negative charge in milk. The purified protein is water insoluble. While it is also insoluble in neutral salt solutions, it is readily dispersible in dilute alkalis and in salt solutions such as sodium oxalate and sodium acetate.
Human beta-casein is the major protein found in human milk. The protein binds to calcium at its phosphorylated regions, which in turn are highly conserved. The calcium then binds the caseins together and forms micelles, which better enable it to be ingested by infants. It also has opioid type effects on newborn sleeping patterns. The protein, as a whole, is disordered and is characterized as a random coil protein. This structure can be modified to some extent with an increase of temperature.
Casein paint is a fast-drying, water-soluble medium used by artists. Casein paint has been used since ancient Egyptian times as a form of tempera paint, and was widely used by commercial illustrators as the material of choice until the late 1960s when, with the advent of acrylic paint, casein became less popular. It is still widely used by scene painters, although acrylic has made inroads in that field as well.
Casein-based glues were popular for woodworking, including for aircraft, as late as the de Havilland Albatross airliner of 1936. Casein glue is also used in transformer manufacturing (specifically transformer board) due to its oil permeability. While largely replaced by synthetic resins, casein-based glues still have a use in certain niche applications, such as laminating fireproof doors and the labeling of bottles.
Cheese consists of proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. It is produced by coagulation of casein. Typically, the milk is acidified and then coagulated by the addition of rennet, containing a proteolytic enzyme, typically obtained from the stomachs of calves. The solids are separated and pressed into final form.
Unlike many proteins, casein is not coagulated by heat. During the process of clotting, milk-clotting proteases act on the soluble portion of the caseins, κ-casein, thus originating an unstable micellar state that results in clot formation. When coagulated with chymosin, casein is sometimes called paracasein. Chymosin (EC 184.108.40.206) is an aspartic protease that specifically hydrolyzes the peptide bond in Phe105-Met106 of κ-casein, and is considered to be the most efficient protease for the cheese-making industry (Rao et al., 1998). British terminology, on the other hand, uses the term caseinogen for the uncoagulated protein and casein for the coagulated protein. As it exists in milk, it is a salt of calcium.
Plastics and fiber/fibre
Some of the earliest plastics were based on casein. In particular, galalith was well known for use in buttons. Fiber can be made from extruded casein. Lanital, a fabric made from casein fiber (known as Aralac in the United States), was particularly popular in Italy during the 1930s. Recent innovations such as QMilch are offering a more refined use of the fiber for modern fabrics.
An attractive property of the casein molecule is its ability to form a gel or clot in the stomach, which makes it very efficient in nutrient supply. The clot is able to provide a sustained slow release of amino acids into the blood stream, sometimes lasting for several hours.
Medical and dental uses
Casein-derived compounds are used in tooth remineralization products to stabilize amorphous calcium phosphate (ACP) and release the ACP onto tooth surfaces, where it can facilitate remineralization.
Although research has shown high rates of use of complementary and alternative therapies for children with autism, including gluten and/or casein exclusion diets, as of 2008[update] there is a lack of evidence for the efficacy of these diets. A 2006 review of seven studies indicated that, although all reported benefits of exclusion diets in reducing autism symptoms, all suffered design flaws, and there was not enough evidence overall to justify recommending exclusion diets to patients.
A1/A2 beta caseins in milk
According to Food Standards Australia New Zealand (FSANZ), "Milk contains many types of proteins. The proportion of various proteins can be quite different in the milk from different breeds of cows and in the milk from other animals.
Of the six major protein types in cow's milk, four are casein proteins and the other two are whey proteins. The caseins usually make up about 80% of the protein in cow's milk. One of the major caseins is beta -casein. There are different beta casein types, but the most common are beta casein A1 (milk high in this type is known as A1 milk) and beta casein A2 (milk high in this type is known as A2 milk).
Certain breeds of cows, such as Friesians, produce mostly A1 milk, whereas other breeds, such as Guernseys, as well as sheep and goats, produce mostly A2 milk. Milk produced in Australia and New Zealand is normally a mix of A1 and A2 milks."
The European Food Safety Authority carried out a literature review in 2009 concluding "a cause and effect relationship is not established between the dietary intake of BCM7, related peptides or their possible protein precursors and non-communicable diseases" (see A2 milk). Studies supporting these claims have had significant flaws, and the data are inadequate to guide autism treatment recommendations.
"A2 Milk" is a trademark of the A2 Corporation Ltd. of New Zealand.
Casein compared to soy
A study done with rabbits indicated that casein can induce hypercholesterolemia. The rabbits that were fed casein protein diets significantly raised cholesterol levels. The rabbits that were fed soy protein diets had reduced cholesterol.
Soy protein has been found to promote more weight loss in mice than casein, when calorie and protein amounts were controlled for. 
A small fraction of the population is allergic to casein and must avoid it in the same way as any other food allergen. There is also a belief that some people have non-allergy sensitivities to casein. Casein has a molecular structure quite similar to that of gluten. Thus, some gluten-free diets are combined with casein-free diets and referred to as a gluten-free, casein-free diet.
Altering the effects of polyphenols
A study of Charité Hospital in Berlin by Lorenzo et al., published in The European Heart Journal, showed adding milk to tea causes the casein to bind to the molecules in tea that cause the arteries to relax, especially a catechin molecule called EGCG, although a more recent study by Reddy et al. (2005) suggests the addition of milk to tea does not alter the antioxidant activity in vivo, and the cardiovascular effect remains controversial.
A study published in the journal Free Radical Biology and Medicine found that consuming 200 mL of whole milk (vs. water control beverage) abolished the 6.1% increase in plasma reducing and chain-breaking antioxidant potential that resulted from consuming 200 g of blueberries, and reduced the peak plasma concentrations of caffeic and ferulic acids, "as well as the overall absorption (AUC) of caffeic acid." The authors did not specifically associate this with the milk's casein content, however. Reviewing previous studies on the impact of milk on absorption of polyphenols, the authors say, "It is a matter of fact that the discrepancy of the results in humans is remarkable, with half the reports suggesting a lack of effect and the other half suggesting an inhibitory effect of milk."
Caseinate salts have been shown to reduce the bioavailability of some drugs, including phenytoin. A patient on this drug should consult their doctor about altering their diet so that the efficacy of the drug is not diminished.
The China Study on cancer
The China Study was a human study that claimed to be the largest ever study on human subjects, with the support of the Chinese government and provincial governments across China. It concluded that populations with greater than 10% of the protein in their diet from casein were at risk of cancer due to casein acting as a cancer promoter. Neal D. Barnard focuses on the addictive nature of milk products and opiate products associated with A1 milk in particular, and notes that "The problem with milk is not simply its casein—that's the part that produces the casomorphin opiates. The nutrient 'package' in milk—loads of sugar (lactose), animal protein, and fat—triggers the production of IGF-I in the body, and that may be the reason it is linked to certain forms of cancer."
- A2 milk – high in β-casein
- Galalith – a casein-derived plastic
- Milk skin
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- A1 and A2 Milk (14 September 2007)
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- Healing Thresholds – summarizes scientific evidence on casein-free diets and other therapies for autism
- Eating without Casein a practical guide to eating and living without casein
- Caseins at the US National Library of Medicine Medical Subject Headings (MeSH)
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