Everything about Casein totally explained
» See Casein paint for information about casein usage in artistic painting.
Casein (from
Latin caseus "cheese") is the predominant
phosphoprotein (αS1, αS2, β,
κ) that account for nearly 80% of proteins in
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
rennet, 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's a
salt of
calcium. Casein isn't 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.
Casein consists of a fairly high number of
proline peptides, which don't interact. There are also no disulfide bridges. As a result, it has relatively little
secondary structure or
tertiary structure. Because of this, it can't
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. The purified protein is water insoluble. While it's also insoluble in neutral salt solutions, it's readily dispersible in dilute
alkalis and in salt solutions such as sodium
oxalate and sodium
acetate.
Applications
In addition to being consumed in milk, casein is used in the manufacture of
adhesives,
binders, protective
coatings,
plastics (such as for knife handles and
knitting needles),
fabrics,
food additives and many other products. It is commonly used by
bodybuilders as a slow-digesting source of
amino acids as opposed to the fast-digesting whey protein, and also as an extremely high source of
glutamine (post-workout). Another reason it's used in bodybuilding is because of its anti-catabolic effect, meaning that casein consumption inhibits protein breakdown in the body. Casein is frequently found in otherwise nondairy cheese substitutes to improve consistency, especially when melted. An enzymatic
hydrolysate of casein to its individual amino acids, called "NZ-Amine" is commonly used as a constituent of
agar plates in molecular biology or to supplement the protein content of foods.
Controversy
Opioid
Casein has been documented to break down to produce the peptide
casomorphin, an
opioid that appears to act primarily as a
histamine releaser. Casomorphine is suspected by some sources to aggravate the symptoms of autism However, a 2006 review concluded that insufficient evidence existed to support the use of elimination diets (for example, casein or gluten free) in the treatment of autism spectrum disorders. More importantly preliminary data from the first and only double-blind randomized control trial - reported in the Journal of autism and developmental disorders - of a gluten- and casein-free diet showed no changes in groups on and off the diet. At this point it's premature to suggest that casein- or gluten-free diets can help children with autism spectrum disorders.
Casein-free diet
Casein has a molecular structure that's quite similar to that of gluten. Thus, most gluten-free diets are combined with casein-free diets and referred to as a
gluten-free, casein-free diet. Casein may also be a trigger of migraines and other types of headaches. Casein may also be linked to the promotion of cancer and other diseases which was discovered in the 1980's by nutrition and health researcher, Dr. T. Colin Campbell, author of
The China Study. Casein is often listed as sodium caseinate, calcium caseinate or milk protein. These are often found in energy bars, drinks as well as packaged goods.
Blocking positive effects of tea
A study of
Charité Hospital in Berlin showed that adding milk to tea will block some of the normal, healthful effects that tea has in protecting against
cardiovascular disease (Lorenz 2007). It does this because casein from the milk binds to the molecules in tea that cause the arteries to relax, especially a
catechin molecule called
EGCG. One of the researchers told
New Scientist magazine that "[i]t probably also blocks tea's effect on other things, such as cancer." However a similar study by Reddy et. al. (2005) suggests that the addition of milk to tea doesn't alter the antioxidant activity in vivo and the cardiovascular effect remains controversial.
Further Information
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