Biological source of sodium alginate
Sodium alginate is sodium salt of alginic acid, obtained by treating alginic acid with sodium carbonate. Alginic acid is obtained from algal growth of species of family Phaeophyceae (brown algae). Family Phaephyceae consists of around fifteen hundred species of multicellular marine brown algae.The common species of this algae family are Macrocystis pyrifera, Ascohyllum nodosum, Laminaria digitata and Laminata hyperborean.
Algin producing sea weeds are found in Pacific and Atlantic oceans. Coastlines of U.S.A, Canada, Japan, Australia and Scotland are rich in brown algae. It is also found in Arabian sea near to coast of Gujarat. Commercial cultivation is also now done in seas of China and Korea.
Identifiers and properties
Algin, Sodium polymannuronate
Molar weight(single structural unit)
198.11(theoretical), 222(actual average)
Molar mass (Macromolecule)
10,000 to 60,000
Sanford first patented alginic acid in 1880's. The patent explains how sodium alginate can be extracted using mild acids and sodium carbonate. Between 1896 to 1898 Krefting managed to prepare a purified form of alginic acid, then in 1930, almost 30 years later, Nelson and Cretcher proposed structure of alginic acid.
The first commercial production of alginic acid commenced in U.S.A in 1929. Since then it is being produced on commercial scale in Japan, United Kingdom, Norway, France and North America.
The United States Pharmacopeia describes pharmaceutical grade sodium alginate as practically odourless, tasteless, coarse or fine powder, yellowish white in colour. It is soluble in water, forms a viscous, colloidal solution, but insoluble in hydroalcoholic solutions containing more than 30% alcohol by weight. It is also insoluble chloroform and ether. It precipitates from acidic solutions if pH reaches less than 3.
1% solution of sodium alginate at 20 o C, may have viscosity between 20 to 400 centipoises.
FNP 52 (Compendium of Food Additive Specifications), describes sodium alginate as white to yellowish brown filamentous, grainy, granules or powder. Food grade sodium alginate should loose more than 15% of weight when heated at 105 o C for four hours.
Sodium alginate used, as food additives should not contain more than 3mg/Kg of arsenic and not more than 5mg/kg of Lead when measured using tests specified in FNP 52 respectively.
Cultivation and harvesting of brown algae
Nylon ropes are seeded with spores of brown algae. The ideal spore solution should contain 10,000 to 40,000 spores per ml as per the culture method used. These ropes are then introduced in sea during autumn and harvested during winters. This fast growing algae species lives 8 to 12 years, and can grow up to 10 inches per day.
Giant kelps found in Pacific Ocean can be 15 to 1500 meters in width and many kilometers in length. Mechanical harvesting is done four times in a year.
It is extracted from the cell walls of brown colour marine algae. The harvested weeds are dried, milled and extracted with dilute sodium carbonate solution that results in a pasty mass. This mass is then diluted to separate insoluble impurities. It is then treated either with sulfuric acid to obtain insoluble alginic acid. Insoluble alginic acid is then collected and washed thoroughly. The alginic acid obtained after washing is treated with sodium carbonate to make sodium alginate.
For use in foods and drugs it is heat sterilized. Preservatives are added to prevent microbial degradation. Solution of sodium alginate should not be stored in metal containers.
Uses of sodium alginate
In food industry sodium alginate is used as stabilizer, thickener, gelling agent and emulsifier. It is used in preparation of creams, pastes, gellies, ice creams, etc.
It is used as a thickening agent in reactive dyestuff used in textile screen-printing and carpet jet printing.
Pharmaceutical industry uses sodium alginate as suspending and thickening agent. It is less used as emulsifying agent as better alternatives are available. Sodium alginate is sterilized by heating in autoclave.
- Pharmacognocy by Dr. C.K.Kokate P.hd, Mr. A.P Purohit M.Pharm, S.B Gokhale M. Pharm
- Journal of Applied Phycology (2006) 18: 259–267,Farming of the giant kelp Macrocystis pyrifera in southern Chile for development of novel food products Alfonso Gutierrez1, Tom´as Correa1, Ver´onica Mu˜noz, Alejandro Santiba˜nez,Roberto Marcos, Carlos C´aceres & Alejandro H. Buschmann.
- FNP 52 Addendum 3 (1995)
- United States Pharmacopeia and the National Formulary (USP-NF)