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Alginate is usually the salts of alginic acid, but it can also refer to derivatives of alginic acid and alginic acid itself; in some publications the term “algin” is used instead of alginate. Alginate is present in the cell walls of brown algae, as the calcium, magnesium and sodium salts of alginic acid. Its colour ranges from white to yellowish-brown. It is sold in filamentous, granular, or powdered forms.

Macrocystis pyrifera, the largest species of giant kelp

Molecular Structure

Alginates are refined from brown seaweeds. Throughout the world, many of the brown seaweeds are harvested to be processed and converted into sodium alginate.

Brown seaweeds range in size from the giant kelp Macrocystis pyrifera which can be 20–40 meters long, to thick, leather-like seaweeds from 2–4 m long, to smaller species 30–60 cm long.


Alginates from different species of brown seaweed vary in their chemical structure resulting in different physical properties of alginates. Some species yield an alginate that gives a strong gel, another a weaker gel, some may produce a cream or white alginate, while others are difficult to gel and are best used for technical applications where colour does not matter.

Sodium alginate (NaC6H7O6) is the sodium salt of alginic acid. Sodium alginate is a gum.

Potassium alginate (KC6H7O6) is the potassium salt of alginic acid.

Calcium alginate (CaC12H14O12), is made from sodium alginate from which the sodium ion has been removed and replaced with calcium (ion exchange).


Sodium alginate is used in many industries including food, animal food, fertilisers, textile printing, and pharmaceuticals. Food grade alginate is an approved ingredient in processed and manufactured foods as a thickening agent for drinks, ice cream, instant desserts, puddings, cosmetics, and as a gelling agent for jellies. Sodium alginate is mixed with soybean protein to make meat analogue.

Sodium Alginate has the E Number E 401.

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.

Alginate is used as an ingredient in various pharmaceutical preparations, in which it combines with bicarbonate to inhibit gastroesophageal reflux.

Sodium alginate is used as an impression-making material in dentistry, prosthetics, lifecasting, and for creating positives for small-scale casting.

Calcium alginate is used in different types of medical products, including skin wound dressings to promote healing.

Alginate is also used for waterproofing and fireproofing fabrics.