alginate

(botany) An algal polysaccharide that is a major constituent of the cell walls of brown algae.

A major constituent (10–47% dry weight) of the cell walls of brown algae. Extracted for its suspending, emulsifying, and gelling properties, it is one of three algal polysaccharides of major economic importance, the others being agar and carrageenan. The chief sources of alginate are members of the family Fucaceae (rockweeds) and the order Laminariales (kelps), harvested from naturally occurring stands on North Atlantic and North Pacific shores.

Because of its colloidal properties, alginate finds numerous industrial applications, especially in the food, textile, paper, printing, paint, cosmetics, and pharmaceutical industries. About half of the consumption is in the making of ice cream and other dairy products, in which alginate prevents the formation of coarse ice crystals and provides a smooth texture. As an additive to paint, it keeps the pigment in suspension and minimizes brush marks. An alginate gel is used in making dental impressions. See also Agar; Carrageenan; Ice cream; Milk; Phaeophyceae.

Salts of alginic acid found in many seaweeds as calcium salts or the free acid. Chemically, alginic acid is a non-starch polysaccharide composed of mannuronic acid units.

Iron, magnesium, and ammonium salts of alginic acid form viscous solutions and hold large amounts of water. They are used as thickeners, stabilizers, and gelling, binding, and emulsifying agents in food manufacture, especially in ice cream and synthetic cream. Trade name Manucol.

A salt of alginic acid (for example, sodium alginate), which, when mixed with water in accurate proportions, forms an irreversible hydrocolloid gel used for making impressions. See also hydrocolloid, irreversible.

A salt of alginic acid, a colloidal substance from brown seaweed; used, in the form of calcium, sodium or ammonium alginate, as foam, clot or gauze for absorbable surgical dressings. Also used as an irreversible hydrocolloid impression material in dentistry for making impressions of jaws in the preparation of orthodontic appliances.