Alginic acid

• Algin
• E 400 - E 405

A02BX13

White solid

Fixed

0.56 g · cm -3

Insoluble in cold water, slightly soluble in boiling water

> 5000 mg · kg -1 ( LD50, rat, oral)

Alginic acid and alginic is formed of brown algae, and by some bacteria (such as Azotobacter ). In the algae, it is the structuring element of the cell wall represents the intercellular gel matrix gives the alga both flexibility and strength. Algin is a by-product, and others in the recovery of iodine from seaweed in the wet process. However, it is also directly extracted for use in the food, as well as the pharmaceutical and cosmetics industry from the brown algae. Salts of alginic acid are generally referred to as alginates. Alginate is used primarily as a thickener or gelling agent used.

Extraction and production

The recovery of the brown algae is done in part by special trawlers " harvest " the seabed. However, it is still common that the algae are collected after storms on the beach. As algae genera for the commercial production of alginate used, among other Laminaria, Ecklonia, Macrocystis, Lessonia, Ascophylum and Durvillea. The collected algae are grossly free from dirt and impurities and dried. After drying, they are supplied to the Alginatproduzenten. In a first process step, the algae are washed and ground. Then, the alginate is extracted and purified by means of filtration and precipitation steps. In addition to the one used in the food industry, most commonly sodium alginate ( E 401 ) are provided for by the following salts of alginic acid: potassium ( E 402 ), ammonium (E 403), calcium alginate (E 404) and propylene glycol alginate (PGA, E 405).

Structure

Alginate is a polysaccharide consisting of the two uronic acids, α -L -guluronic acid ( Gulua ) and β -D -mannuronic acid ( Manua ), which are 1,4- glycosidically linked in varying proportions to form linear chains. It forms homopolymeric regions in which there are mannuronic or guluronic acid as blocks. These blocks are referred to as GG or MM blocks. In the GG and MM- blocks there is a kind of folded structure, which plays an essential role in the gelation. In particular, the GG- blocks form a regular zigzag structure. The mean molecular weight is 48000-186000.

Function

Alginate may result in low calcium solutions to a viscosity education. However, the primary function of the gelling. Gelation occurs by incorporation of calcium ions in the zigzag structure of GG blocks. In this zone, then overlying the zigzag structure of another Alginatmoleküls. It is thus to form three-dimensional structures. Because the calcium is in the structure, such as an egg in the box is also known as " egg-box model " or " model eggbox " this model. Because this reaction occurs very abruptly with the calcium, is working in practice with various methods to drain controls the reaction. For this purpose, often poorly soluble calcium salts are used, which gradually release the calcium by slow acidification. Also, look for sequestrants use that can bind a portion of the calcium. Instead of calcium, other divalent cations such as barium, to be used to gel the alginate.

Salts of alginic acid are soluble in water, often due to the high viscosity of the resulting solution to stir overnight with warming necessary to avoid formation of lumps. 1 - to 2 - percent solutions gel upon contact with a sufficiently concentrated calcium solutions spontaneously and rapidly. Algin can be used as finishing agents for textiles and fabrics, as well as the production of photographic papers. As a food additive it bears the designation E 400

Applications

Food technology

In the food industry, alginates as an emulsifier, gelling agents, coating agents or thickening agents. In the EU, alginic acid and the sodium, potassium, ammonium and calcium salts as a food additive with the E numbers are 400-405 for all approved additives for products - even for "organic " products - approved. Alginates are not absorbed by the body and are considered safe. However, larger amounts can the absorption of calcium and trace elements such as iron and lower in animal experiments, a slight impairment of protein digestion was observed. However, there are no health concerns.

Alginates are often found in diet and light products, baked goods, frozen foods, mayonnaise, salad dressings, ice cream, in meat and canned vegetables and soups. It also occurs in the manufacture of processed cheese in combination with sodium citrate ( E331 ) and sodium phosphate ( E 339 ).

Alginates are also used in the so-called molecular cuisine, where they are used for the production of art or fruit caviar.

In addition, it is also used in cosmetic products.

Medicine

In medicine, calcium alginate dressings are used to supply superficial and profound wounds. Calcium prevents sticking of the casting material to the wound by the Na ions from the wound exudate to Ca2 exchange and in the associated expansion process forms a gel that keeps the wound moist and promotes the wound healing.

In surgery, alginate is used as a wound dressing or wound filler, in particular to have to clean and heal chronic wounds.

Alginate is also used as a biomaterial. By encapsulating human cell tissue with alginate, it is possible to store a foreign body such as donor cells, without that these can be recognized and destroyed by the immune system. The cells then take an active part in the metabolism of the recipient. For example, insulin-producing cells can be transferred from donors to patients with diabetes, which are then no longer dependent on spraying.

Alginate is also used as a medicine for heartburn, is being exploited, that the drug is not metabolized and forms a physical barrier between the acidic contents of the stomach and esophagus. Here it forms with other components ( calcium carbonate / potassium bicarbonate ) a tough foam, which lies on the stomach contents, thus preventing a renewed reflux.

Alginate has been found frequently used in laboratories, in particular in the cell culture in the past. Its ability to gel by addition of calcium, and (for example by means of EDTA) to liquefy after complexing of the calcium again allows temporary culture of cells in three-dimensional structures, and then the recovery of the cells, without this enzymatic, thermal or mechanical damage inflict, as often happens with other gels.

Dentistry

Alginate is often used in dental practice for molding the rows of teeth. As alginate impression material is physiologically safe and allows impressions of reasonable accuracy and detail. Improper processing the alginate dries out and becomes unusable. ( For precision impressions, however, impression materials are used with high detail and sharpness characters as especially elastomers such as polyethers and silicones). The impression material is in suitable carriers of metal or plastic is introduced into the mouth (known as impression tray ). The conventional in dentistry Abformwerkstoff usually still contains sodium calcium sulfate ( gypsum), sodium phosphate as a retarder, and a large amount of diatomaceous earth ( diatomaceous earth ).

Furthermore, alginate solutions are used for isolation of materials against each other, that is, to prevent that connect these substances together. In dental technology, a plaster model with an alginate solution, for example, been painted over, so a plastic prosthesis made ​​on this model can then solve problems from the plaster model ( insulation plaster from plastic).

Körperabformungen

Alginate is used by artists in the field of Körperabformungen. The material is applied over a large area on the abzuformende part of the body. Within minutes, the alginate binds from a silicone-like mass. Then, still spread on the solidified alginate few layers of plaster bandages to get the proportions and to stabilize the mold for pouring later. The plaster bandages harden very quickly so that the negative mold can be shortly afterwards carefully detached and removed from the body. By using alginate a very detailed and accurate pore impression is reached. After modeling plaster is mixed and the negative form so poured all over. After a drying time of approximately 24 hours can then be removed from the mold from the alginate plaster shell and then processed the Positivabformung.

Textile printing

Alginate is used as a thickener in textile printing.