algin

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Variant: alginic acid

A complex polysaccharide occurring in the cell walls of the brown algae (Phaeophyta). Algin strongly absorbs water to form a viscous gel. It is produced commercially from a variety of species of Laminaria and from Macrocystis pyrifera in the form of alginates, which are used mainly as a stabilizer and texturing agent in the food industry.

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Source: Brown algae, commonly including members of the following genera: Macrocystis, Laminaria, and Ascophyllum.

Common/vernacular names: Algin, salts of alginic acid (alginates), and particularly sodium alginate.

Algin is a collective term for the hydrophilic colloidal substance isolated from certain brown algae (class Phaeophyceae). The most commonly used algae include members of the following genera: Macrocystis, Laminaria, and Ascophyllum.

A major source of algin in the United States is Macrocystis pyrifera (L.) C. A. Agardh. or "giant kelp" that grows along the West Coast of North America. Other sources include Ascophyllum nodosum (L.) LeJolis and Laminaria digitata (L.) Edmonson and related species that are used by countries bordering the Atlantic Ocean. Laminaria species are also used by Japanese producers.

The process for algin manufacture basically involves a prewash of the seaweed whereby undesirable salts are leached out and removed, followed by extraction with a dilute alkaline solution that solubilizes the alginic acid present in the seaweed. The resulting thick and viscous mass is clarified and the algin is obtained as free alginic acid on treatment with mineral acids. The alginic acid can then be converted to sodium alginate. Sodium alginate is the major form of algin currently in use.

The major producing countries include the United States, UK, Norway, France, and Japan.

Alginic acid and its calcium salt are insoluble in water, but its ammonium, sodium, potassium, and magnesium salts as well as its propylene glycol ester are readily soluble in cold and hot water in which they form viscous solutions. The viscosity of algin solutions depends on various factors including concentration, pH, degree of polymerization (DP), temperature, and presence of polyvalent metal ions. Viscosity increases with DP; it decreases with increase in temperature but will regain its original value on cooling to its initial temperature, provided the solutions are not held above 50 °C for long periods. Between pH 4 and 10 the viscosity of algin solutions is generally stable.

Algin solutions form gels with calcium ions due to the formation of insoluble calcium alginate. These gels are not thermally reversible but may be liquefied by calcium sequestrants.

Propylene glycol alginate is more acid-tolerant than the other alginates. Its solutions are stable below pH 4 (down to pH 2.6).

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the sodium salt of alginic acid.

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