Sodium Alginate

| Home | | Pharmacognosy |

Chapter: Pharmacognosy and Phytochemistry : Drugs Containing Carbohydrates and Derived Products

Sodium alginate is the sodium salt of alginic acid. Alginic acid is a polyuronic acid composed of reduced mannuronic and glucoronic acids, which are obtained from the algal growth of the species of family Phaeophyceae. The common species are Macrocystis pyrifera, Laminaria hyperborea, Lami-naria digitata, Ascophyllum nodosum and Durvillaea lessonia. It is a purified carbohydrate extracted from brown seaweed (algae) by treatment of dilute alkali.


SODIUM ALGINATE

 

 

Synonyms

 

Algin, Alginic acid sodium salt, Sodium polymannuronate, Kelgin, Minus, Protanal.

 

 

Biological Source

 

Sodium alginate is the sodium salt of alginic acid. Alginic acid is a polyuronic acid composed of reduced mannuronic and glucoronic acids, which are obtained from the algal growth of the species of family Phaeophyceae. The common species are Macrocystis pyrifera, Laminaria hyperborea, Lami-naria digitata, Ascophyllum nodosum and Durvillaea lessonia. It is a purified carbohydrate extracted from brown seaweed (algae) by treatment of dilute alkali.

 

Geographical Source

 

Sea-weeds are found in Atlantic and Pacific oceans, par-ticularly in coastal lines of Japan, United States, Canada, Australia and Scotland. In India, it is found near the coast of Saurashtra. The largest production of algin is in United States and U.K.

 

Collection and Preparation

 

The brown coloured algae are used for extraction of alginic acid. The colour is due to carotenoid pigment present in it. M. pyrifera, the principal source for global supply, is a perennial plant that lives from 8 to 12 years, and grows, as much as, 30 cm per day. This giant kelp is found mainly in Pacific Ocean. It grows on stands from 15 m to 1.5 km in width and several km in length. The mechanical harvesting is done about four times a year.

Alginic acid is present in the cell wall. The seaweeds are harvested, dried, milled and extracted with dilute sodium carbonate solution which results in a pasty mass. It is then diluted to separate insoluble matter. Soft water is only used for extraction purposes, so as to avoid incompatibilities. It is treated with calcium chloride or sulphuric acid for conversion into either calcium alginate or insoluble alginic acid, which is collected and purified by thorough washing. If calcium is used, it is treated with hydrochloric acid. Alginic acid so collected is treated with sodium carbonate for neutralization and converted into sodium salt. The alginic acid content on dry solid basis varies from 22% to 35% in all the varieties of brown algae.

 

Morphology

 


 

History

 

Alginic acid, a hard, horny polysaccharide, was first isolated by the English chemist Stanford in 1883 and in Britain was first marketed in 1910. The commercial production of algin first began in 1929 in United States Since then it is produced in U.K., France, Norway and Japan. The present total algin production is estimated to be more than 15,000 tones per annum.

 

Identification Tests

 

1)  Precipitate formation with Calcium chloride

 

To a 0.5% solution of the sample in sodium hydroxide, add one-fifth of its volume of a 2.5% solution of calcium chloride. A voluminous, gelatinous precipitate is formed. This test distinguishes sodium alginate from gum arabic, sodium carboxymethyl cellulose, carrageenan, gelatin, gum ghatti, karaya gum and tragacanth gum.

 

2) Precipitate formation with Ammonium sulphate

 

To a 0.5% solution of the sample in sodium hydroxide, add one-half of its volume of a saturated solution of ammonium sulphate. No precipitate is formed. This test distinguishes sodium alginate from agar, sodium carboxymethyl cellulose, carrageenan, methyl cellulose and starch.

 

3) Test for alginate

 

Moisten 1–5 mg of the sample with water and add 1 ml of acid ferric sulphate. Within 5 min, a cherry-red colour develops that finally becomes deep purple.

 

1% solution in water forms heavy gelatinous precipitate with dilute sulphuric acid.

 

Chemical Constituents

 

Algin consists chiefly of the sodium salt of alginic acid, a linear polymer of L-guluronic acid and D-mannuronic acid; the chain length is long and varies (mol. wt. from 35,000 to 1.5 × 106) with the method of isolation and the source of the algae. Mannuronic acid is the major component.. The alginic acid molecule appears to be a copolymer of 1, 4-linked mannopyranosyluronic acid units, of 1, 4-linked gulopyranosyluronic acid units, and of segments where these uronic acids alternate with 1, 4-linkages.

 

Uses

 

High and medium viscosity grades of sodium alginate are used in the preparation of paste, creams and for thickening and stabilizing emulsions. It is a good suspending and thickening agent, but a poor emulsifying agent. It is used as binding and disintegrating agent in tablets and lozenges. In food industry, it is used for the preparation of jellies, ice cream, etc. It is also used in textile industry. For pharmaceutical purposes, when desired, it is sterilized by heating in an autoclave. The solution of sodium alginate should not be stored in metal containers. It is preserved by the addition of 0.1% of chloroxylenol, chlorocresol, benzoic acid or parabenes. Potassium, aluminium and calcium alginates are also used medicinally.

 

Capsules containing sodium alginate and calcium carbon-ate are used to protect inflamed areas near the entrance to the stomach. The acidity of the stomach causes formation of insoluble alginic acid and carbon dioxide; the alginic acid rises to the top of the stomach contents and forms a protective layer.

 

Marketed Product

 

Each 100 ml of Lamina G solution manufactured by Taejoon Pharm Co. Ltd, Seoul contains 5.0g of sodium alginate. It is mainly used for the treatment of Gastric and duodenal ulcer, erosive gastritis, reflux esophagitis (usual dosage is 20–60 ml orally three to four times daily before meal) and Hemostasis in gastric biopsy (usual dosage is 10–30 ml by endoscope, followed by 30 ml orally).

 

Contact Us, Privacy Policy, Terms and Compliant, DMCA Policy and Compliant

TH 2019 - 2022 pharmacy180.com; Developed by Therithal info.