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Casein (from Latin caseus "cheese") is the predominant phosphoprotein (αS1, αS2, β, κ) that accounts for nearly 80% 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.

Contents

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.

Casein has been reported to reduce tooth decay [1].

Protein Supplement

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Slow Acting

An attractive property of the casein micelle is its ability to form a gel or clot in the stomach[2]. 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[3]. This provides better nitrogen retention and utilization by the body.[4]

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.[5]

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.[6] 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.[7] 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."[8] 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.[9]

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. Certain breeds of cows, such as Fresians, the main breed in Europe, produce A2 milk which is A1 free, alongside other breeds, such as Guernseys, as well as sheep and goats, which also produce mostly A2 milk[10]

In 1993 Professor Bob Elliott from Auckland University, looking into the incidence of Type 1 diabetes amongst Samoan children started investigating potential links with milk and the proportion of A1 to A2 beta-casein proteins - which varies considerably between the herds in different countries. One of the scientist involved, Dr Corann McLachlan, teamed up with entrepreneur Howard Patterson to form A2 Corporation, licensing technology to quickly test the DNA of cattle to see which type they produce, a their "A2 milk" trademark.[10]

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.[11]

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[12] and the cardiovascular effect remains controversial.[13][14] 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.

Notes

  1. ^ Glenn Walker, Fan Cai, Peiyan Shen, Coralie Reynolds, Brent Ward, Christopher Fone, Shuji Honda, Megumi Koganei, Munehiro Oda and Eric Reynolds (2006). "Increased remineralization of tooth enamel by milk containing added casein phosphopeptide-amorphous calcium phosphate". Journal of Dairy Research 73 (1): 74–78. doi:10.1017/S0022029905001482. PMID 16433964.  
  2. ^ "100% Casein Protein". http://www.optimumnutrition.com/products/100-casein-protein-p-219.html.  
  3. ^ Boirie, Y., Dangin, M., Gachon, P., Vasson, M.P., Maubois, J.L. and Beaufrere, B. (1997) "Slow and fast dietary proteins differently modulate postprandial protein accretion." Proclamations of National Academy of Sciences 94, 14930-14935.
  4. ^ Jay R. Hoffman and Michael J. Falvo (2004). "Protein - Which is best?". Journal of Sports Science and Medicine (3): 118–130.  
  5. ^ Miura, Y.; Kato, H.; Noguchi, T. (1992). "Effect of dietary proteins on insulin-like growth factor-1 (IGF-1) messenger ribonucleic acid content in rat liver". British Journal of Nutrition 67 (2): 257. doi:10.1079/BJN19920029. PMID 1596498.   edit
  6. ^ Kurek M, Przybilla B, Hermann K, Ring J (1992). "A naturally occurring opioid peptide from cow's milk, beta-casomorphine-7, is a direct histamine releaser in man". Int Arch Allergy Immunol. 97 (2): 115–20. doi:10.1159/000063326. PMID 1374738.  
  7. ^ Christison GW, Ivany K (2006). "Elimination diets in autism spectrum disorders: any wheat amidst the chaff?". J Dev Behav Pediatr 27 (2 Suppl 2): S162–71. doi:10.1097/00004703-200604002-00015. PMID 16685183.  
  8. ^ Elder JH, Shankar M, Shuster J, Theriaque D, Burns S, Sherrill L (April 2006). "The gluten-free, casein-free diet in autism: results of a preliminary double blind clinical trial". J Autism Dev Disord 36 (3): 413–20. doi:10.1007/s10803-006-0079-0. PMID 16555138.  
  9. ^ Millward C, Ferriter M, Calver S, Connell-Jones G. Gluten- and casein-free diets for autistic spectrum disorder. Cochrane Database of Systematic Reviews 2008, Issue 2. Art. No.: CD003498. DOI: 10.1002/14651858.CD003498.pub3.
  10. ^ a b A1 and A2 Milk (14 September 2007), Food Standards Australia New Zealand
  11. ^ http://www3.interscience.wiley.com/journal/119209344/abstract
  12. ^ Reddy VC, Vidya Sagar GV, Sreeramulu D, Venu L, Raghunath M (2005). "Addition of milk does not alter the antioxidant activity of black tea". Ann Nutr Metab. 49 (3): 189–95. doi:10.1159/000087071. PMID 16020939.  
  13. ^ Prabhakar VR, Venkatesan N (June 2007). "Milk casein and its benefits on cardiovascular risk". Eur Heart J. 28 (11): 1397; author reply 1397–8. doi:10.1093/eurheartj/ehm106. PMID 17483526. http://eurheartj.oxfordjournals.org/cgi/content/extract/28/11/1397.  
  14. ^ Lorenz M, Jochmann N, von Krosigk A, et al. (January 2007). "Addition of milk prevents vascular protective effects of tea". Eur. Heart J. 28 (2): 219–23. doi:10.1093/eurheartj/ehl442. PMID 17213230. http://eurheartj.oxfordjournals.org/cgi/content/extract/ehm107v1.  

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See also

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