Casein

For information about casein usage in artistic painting, see Casein paint.

Casein (from Latin caseus "cheese") is the predominant phosphoprotein (αS1, αS2, β, κ) that accounts for nearly 20% of proteins in cow milk and cheese. Milk-clotting proteases act on the soluble portion of the caseins, K-Casein, thus originating an unstable micellar state that results in clot formation. When coagulated with chymosin, casein is sometimes called paracasein. Chymosin (EC 3.4.23.4) 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. Casein is not coagulated by heat. It is precipitated by acids and by rennet enzymes, a proteolytic enzyme typically obtained from the stomachs of calves. The enzyme trypsin can hydrolyze off a phosphate-containing peptone.

It is used to form a type of organic adhesive.

Description

Casein consists of a fairly high number of proline peptides, which do not interact. There are also no disulfide bridges. As a result, it has relatively little tertiary structure. Because of this, it cannot denature. 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 some resemblance with surfactant-type micellae in a sense that the hydrophilic parts reside at the surface. The caseins in the micelles are held together by calcium ions and hydrophobic interactions. There are several models that account for the special conformation of casein in the micelles (Dalgleish, 1998). One of them proposes that the micellar nucleus is formed by several submicelles, the periphery consisting of microvellosities of κ-casein (Walstra, 1979; Lucey, 2002). Another model suggests that the nucleus is formed by casein-interlinked fibrils (Holt, 1992). Finally, the most recent model (Horne, 1998) proposes a double link among the caseins for gelling to take place. All 3 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.

A casein hydrolysate fraction when complexed with a calcium containing compound has been shown to help with the remineralization of teeth.

Protein supplement

Slow acting

An attractive property of the casein molecule is its ability to form a gel or clot in the stomach. The ability to form this clot 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. This provides better nitrogen retention and utilization by the body.

IGF-1

Plasma immunoreactive IGF-1 concentration in rats given a casein diet was higher than that in rats given a soya-bean-protein or protein-free diet.

Controversies

Opioid

Casein has been documented to break down to produce the peptide casomorphin, an opioid that appears to act primarily as a histamine releaser. Some believe that this casomorphine aggravates the symptoms of autism. A 2006 review of seven studies indicated that although benefits were seen in all studies from the introduction of elimination diets (e.g., casein or gluten free) in the treatment of autism spectrum disorders, none of the studies were performed in a manner to create an unbiased scientific opinion. Preliminary data from the first and only double-blind randomized control trial of a gluten- and casein-free diet "indicated no statistically significant findings even though several parents reported improvement in their children." Research has shown of high rates of use of complementary and alternative therapies (CAM) for children with autism including gluten and/or casein exclusion diets. Evidence for efficacy of these diets is currently unsubstantiated.

A1/A2 Beta caseins

Four casein proteins make up about 80% of the protein in cow's milk. One of the major caseins is beta-casein, of which there are several types, but "A1" and "A2" are the most common. According to the Australian Food Standards Agency:

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.

FSANZ also reports that despite some hypotheses that consumption of A2 milk "provides levels of protection to consumers from autism in children as well as schizophrenia, diabetes and heart disease," the scientific evidence for such claims is "very limited". Additionally, the European Food Safety Authority carried out a literature review in 2009 concluding that "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).

Casein-free diet

Main article: Gluten-free, casein-free diet

Casein has a molecular structure that is 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. Casein is often listed as sodium caseinate, calcium caseinate or milk protein. These are often found in energy bars, drinks, and packaged goods.

A small fraction of the population is allergic to casein.

Dr. T. Colin Campbell argues in The China Study that the milk protein casein, found in milk and many prepared foods, is also a carcinogen.

Altering the effects of polyphenols

A study of Charité Hospital in Berlin by Lorenzo et al., published in The European Heart Journal, showed that 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. A similar study by Reddy et al. (2005) suggests that 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 indicates that casein reduced the peak plasma levels of beneficial polyphenols after the consumption of blueberries.

Sources

• Dalgleish DG (1 November 1998). "Casein micelles as colloids. Surface structures and stabilities". J Dairy Sci. 81 (11): 3013–8. doi:10.3168/jds.S0022-0302(98)75865-5. 
• Green VA, Pituch KA, Itchon J, Choi A, O'Reilly M, Sigafoos J (2006). "Internet survey of treatments used by parents of children with autism". Res Dev Disabil. 27 (1): 70–84. doi:10.1016/j.ridd.2004.12.002. PMID 15919178. CS1 maint: Multiple names: authors list (link)
• Holt C (1992). "Structure and stability of bovine casein micelles". Adv Protein Chem. 43: 63–151. doi:10.1016/S0065-3233(08)60554-9. PMID 1442324. 
• Lucey JA (1 February 2002). "Formation and Physical Properties of Milk Protein Gels". J Dairy Sci. 85 (2): 281–94. doi:10.3168/jds.S0022-0302(02)74078-2. PMID 11913691. 
• Rao MB, Tanksale AM, Ghatge MS, Deshpande VV (1 September 1998). "Molecular and biotechnological aspects of microbial proteases". Microbiol Mol Biol Rev. 62 (3): 597–635. PMC 98927 Freely accessible. PMID 9729602. CS1 maint: Multiple names: authors list (link)
• Walstra P (1979). "The voluminosity of bovine casein micelles and some of its implications". J Dairy Sci UK. 46 (2): 317–22. 
• Engel RW, Copeland DH (1 December 1952). "The influence of dietary casein level on tumor induction with 2-acetylaminofluorene". Cancer Res. 12 (12): 905–8. PMID 13009679. 
• Manninen, A.H. (2002). "Protein metabolism in exercising humans with special reference to protein supplementation. Master thesis" (PDF). Department of Physiology, Faculty of Medicine, University of Kuopio, Finland. 
• Robert H. Demling, Leslie DeSanti (2000). "Effect of a Hypocaloric Diet, Increased Protein Intake and Resistance Training on Lean Mass Gains and Fat Mass Loss in Overweight Police Officers". Annals of Nutrition & Metabolism. 44 (44): 21–29. doi:10.1159/000012817. 
• Campbell, T., and Campbell, Thomas II (2005). The China Study. Benbella Books. p. 6. CS1 maint: Multiple names: authors list (link)

See also

• A2 milk - High in β-casein
• CAS registry number
• K-Casein
• Casomorphin
• Cheese
• Dairy
• Galalith - a casein-derived plastic
• Milk skin

External links

• Healing Thresholds summarizes scientific evidence on casein-free diets and other therapies for autism
• GFCF Diet Support Group
• Information about types of casein protein
• Casein causing headaches
• Eating without Casein Practical guide to milk-free eating
• MeSH Caseins
• Time Magazine, Monday, December 6, 1936 Lanital
• Time Magazine, Monday, August 29, 1938 Wool from Cows, see Achille Staracear:كازين

uk:Казеїн