alginic acid

Alginic acid
Other names	E400
Identifiers
CAS number	9005-32-7
EC number	232-680-1
ATC code	A02BX13
Properties
Molecular formula	(C6H8O6)n
Molar mass	10,000 - 600,000
Appearance	white to yellow, fibrous powder
Density	1.601 g/cm3
Acidity (pKa)	1.5-3.5
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Alginic acid, also called algin or alginate, is a viscous gum that is abundant in the cell walls of brown algae. It ranges from white to yellowish-brown, and takes filamentous, granular and powdered forms. It absorbs water quickly; it is capable of absorbing 200-300 times its own weight in water. ^[1]

Structure

It is a linear copolymer with homopolymeric blocks of (1-4)-linked β-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G) residues, respectively, covalently linked together in different sequences or blocks.

The monomers can appear in homopolymeric blocks of consecutive G-residues (G-blocks), consecutive M-residues (M-blocks), alternating M and G-residues (MG-blocks), or randomly organized blocks.

Forms

Commercial varieties of alginate are extracted from seaweed, including the giant kelp Macrocystis pyrifera, Ascophyllum nodosum, and various types of Laminaria. It is also produced by two bacterial genera Pseudomonas and Azotobacter, which played a major role in the unravelling of its biosynthesis pathway. Bacterial alginates are useful for the production of micro- or nanostructures suitable for medical applications.^[2]

Uses

Alginate absorbs water quickly, which makes it useful as an additive in dehydrated products such as slimming aids, and in the manufacture of paper and textiles. It is also used for waterproofing and fireproofing fabrics, as a gelling agent, for thickening drinks, ice cream and cosmetics, and as a detoxifier that can absorb poisonous metals from the blood.^{[citation needed]}

Alginate is used in various pharmaceutical preparations such as Gaviscon, Bisodol, and Asilone. Alginate is used extensively as a impression-making material in dentistry, prosthetics, lifecasting. It is also used in the food industry, for thickening soups and jellies.

Calcium alginate is used in different types of medical products, including burn dressings that promote healing and can be removed with less pain than conventional dressings.

Also, due to alginate's biocompatibility and simple gelation with divalent cations such as Ca²⁺, it is widely used for cell immobilization and encapsulation.

Alginic acid (alginato) is also used in culinary arts, most notably in the "Esferificación" (Sphereification) techniques of Ferran Adrià of El Bulli in Roses, Girona, where natural juices of fruits and vegetables are encapsulated in bubbles that "explode" on the tongue when consumed. One of the most famous examples of this use of alginic acid was when Ferran Adrià used alginic acid to make apple caviar.^[3]

Due to its ability to absorb water quickly, alginate can be changed through a lyophilization process to a new structure that has the ability to expand. It is used in the weight loss industry as an appetite suppressant.

Sodium alginate

The chemical compound sodium alginate is the sodium salt of alginic acid. Its empirical formula is NaC₆H₇O₆. Its form as a flavorless gum, when extracted from the cell walls of brown algae, is used by the foods industry to increase viscosity and as an emulsifier. It is also used in indigestion tablets and the preparation of dental impressions.

External links

• Alginate seaweed sources
• Alginate properties

References