Sodium alginate

Alginic acid

Names
Other names Alginic acid, E400
Identifiers
CAS Number	9005-32-7 Y
ECHA InfoCard	100.029.697
EC Number	232-680-1
E number	E400 (thickeners, ...)
UNII	8C3Z4148WZ N
Properties
Chemical 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
Pharmacology
ATC code	A02BX13 (WHO)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Alginic acid, also called algin or alginate, is an anionic polysaccharide distributed widely in the cell walls of brown algae, where through binding with water it forms a viscous gum. It is also a significant component of the biofilms produced by the bacterium Pseudomonas aeruginosa, the major pathogen in cystic fibrosis, that confer it a high resistance to antibiotics and killing by macrophages. Its colour ranges from white to yellowish-brown. It is sold in , granular or powdered forms.

Alginic acid 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) or alternating M and G-residues (MG-blocks).

Alginates are refined from brown seaweeds. A wide variety of brown seaweeds of the phylum Phaeophyceae are harvested throughout the world to be converted into the raw material commonly known as sodium alginate. Sodium alginate has a wide use across a wide variety of industries including food, textile printing and pharmaceutical. Dental impression material utilizes alginate as its means of gelling. Alginate is both food and skin safe.

Seaweeds can be classified into three broad groups based on pigmentation: brown, red and green. These broad groups are the Phaeophyceae, Rhodophyceae and Chlorophyceae, respectively. Brown seaweeds are usually large, and range from the giant kelp Macrocystis pyrifera that is often 20 m long, to thick, leather-like seaweeds from 2-4 m long, to smaller species 30–60 cm long. None of the usual seaweeds for alginate production are cultivated. They cannot be grown by vegetative means, but must go through a reproductive cycle involving an alternation of generations. This makes cultivated brown seaweeds too expensive when compared to the costs of harvesting and transporting wild seaweeds. The only exception is for Laminaria japonica, which is cultivated in China for food but the surplus material is diverted to the alginate industry in China.