Casein
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Casein or casein ( lat. Caseus , cheese ', pronounced cheese-in) is the name for the protein content of milk that is processed into cheese and does not end up in the whey . It is a mixture of several proteins (αS1-, αS2-, β-, κ-casein) and is used to store and transport protein, calcium and phosphate to the newborn . Casein, together with calcium phosphate and other constituents, forms micelles in milk that keep the calcium phosphate dissolved and aggregate the milk into a lump in the stomach, which makes digestion easier.
Casein makes up the majority of the proteins in quark and cheese , which get their firm consistency through the coagulation of the casein. Casein is not only used as a food , but also as a binder and pharmaceutical excipient . Casein is one of the most common triggers of cow's milk allergy . The caseins are the most common milk proteins, making up about 80% of the total amount of protein in milk. The other proteins are also grouped together as whey proteins .
composition
As an example, the following table, which lists the components of the cow casein.
| protein | Amount per liter of cow's milk |
Number of amino acids |
UniProt entry |
|---|---|---|---|
| αS1-casein (cow) | 10.7 g | 199 | P02662 |
| αS2-casein (cow) | 2.8 g | 207 | P02663 |
| β-casein (cow) | 8.6 g | 209 | P02666 |
| κ-casein (cow) | 3.1 g | 169 | P02668 |
| 26 g in total |
In contrast to cow's milk, β- and κ-casein are the main proteins in human milk. The table below provides details and links about casein in human milk.
| protein | gene | chromosome | Number of amino acids |
OMIM entry | UniProt entry |
|---|---|---|---|---|---|
| αS1-casein (human) | CSN1S1 | 4q21.1 | 170 | 115450 | P47710 |
| Casein S2α-like A (human) | CSN1S2A | 4q13.3 | 27 | - | Q8IUJ1 |
| β-casein (human) | CSN2 | 4q21.1 | 211 | 115460 | P05814 |
| κ-casein (human) | CSN3 | 4q21.1 | 162 | 601695 | P07498 |
meaning
Casein is the most important source of protein, calcium and phosphate for young mammals. Cow's milk contains 2.6% casein (i.e. about 26 g / L; significantly less in one-legged mammals) and makes up about 80% of total milk protein.
properties
In contrast to most other proteins, micellar casein is heat-resistant up to 120 ° C. If casein has been precipitated from milk by adding acid, it is only slightly soluble in water, so that it has to be neutralized ("digested") with a lye before it can be mixed with water again. The original micellar structure is lost when precipitating with acids.
digestion
The casein is partially broken down by heating, adding acid or , to a greater extent, adding the enzyme pepsin , which makes cheese and quark easier to digest than raw milk.
Casein can act as an allergen in humans and trigger very violent, even life-threatening reactions. This should not be confused with lactose intolerance , which is an enzyme-related intolerance to milk sugar .
The digestion of casein is very slow. It can be up to eight hours. Athletes (especially bodybuilders) make use of this advantage in order to achieve an amino acid supply over several hours (for example overnight).
When casein is digested, an opioid called casomorphine is produced, but studies have shown that it is neither absorbed in intact form via the intestine nor is it able to cross the blood-brain barrier .
Extraction
Native casein is mainly obtained through microfiltration . The particle size serves as the separation criterion. In retentate mainly remain caseins and smaller amounts of whey protein and lactose in permeate are mainly mineral salts, lactose, whey proteins and small amounts of Caseinsubmicellen.
Denatured or functionally altered casein or caseinate can be produced with the aid of acid precipitation and subsequent neutralization using calcium hydroxide, potassium hydroxide or sodium hydroxide solution. The denatured casein is then separated off by filtration or centrifugation . In most cases, the protein to be precipitated is concentrated beforehand using various methods.
use
In addition to being used as food , casein is also used technically as a raw material for various processing purposes. Its use as a binder in casein paints , as casein glue (e.g. as a label glue for labeling ) or as a photoresist in etching technology plays a role here. Casein glue is said to have been used by ancient Chinese and Egyptian carpenters to glue furniture together. Dyers used casein as a binder in dyeing leather and fabrics.
From the end of the 19th century until the 1930s it was the starting material for the plastic Galalith , which u. a. for buttons and jewelry, but also for insulation purposes for electrical systems. Friedrich Ernst Todtenhaupt (1873-1919) made attempts with the Galalith Society at the beginning of the 20th century to make artificial silk from it, but they were unsuccessful. Casein hydrolysates or peptones from casein are used in microbiology to some extent as a component of nutrient media or nutrient solutions for the cultivation of microorganisms, for example in casein-soy-peptone agar .
Casein glue was used as a connector in early wooden aircraft construction until the 1950s.
Historically, casein was also used to study the composition of proteins. The amino acids L- tyrosine (1846 by Justus von Liebig ), L- lysine (1889 by Edmund Drechsel ), L- tryptophane (1902 by Frederick Hopkins ) and L- methionine (1922 by John Howard Mueller ) were isolated from casein.
literature
- The Merck Index, 10th Ed. (1983) Rahway, NJ
Web links
Individual evidence
- ^ The Dairy Science and Technology eBook: Structure: The Casein Micelle , accessed January 9, 2015.
- ↑ T. Nakano, N. Shimojo, Y. Morita, T. Arima, M. Tomiita, Y. Kohno: Sensitization to casein and beta-lactoglobulin (BLG) in children with cow's milk allergy (CMA) . In: Arerugi . 59, No. 2, February 2010, pp. 117-22. PMID 20212353 .
- ↑ German Allergy and Asthma Association on milk protein allergy at daab.de, accessed on May 24, 2018.
- ↑ The Dairy Science and Technology eBook: Dairy Chemistry and Physics: Milk Proteins , accessed January 9, 2015.
- ↑ Milk proteins from Spektrum.de, accessed on May 24, 2018.
- ↑ Nanotechnology in the food industry , Prof. Dr. Herbert Weber, accessed February 2016.
- ^ European Food Safety Authority. February 1, 2009 Review of the potential health impact of β-casomorphins and related peptides
- ↑ S. Hansen: The discovery of proteinogenic amino acids from 1805 in Paris to 1935 in Illinois. Berlin 2015.