Floating in the middle of the Atlantic Ocean sits the Sargasso Sea: a mat of seaweed 2 million square miles wide. The brown algae that make up this vast living carpet are the source of the versatile food additive sodium alginate. The Food and Drug Administration classifies sodium alginate as a "Generally Recognized As Safe" food additive, and it has medical and textile industry uses as well.
Making Sodium Alginate
Sodium alginate is a gummy substance derived from the cell walls of brown algae. The chemical alginate is extracted by treating the seaweed with an acidic solution. This is followed by another treatment with an alkaline solution such as sodium hydroxide. The resulting mixture is filtered and processed further until a clear solution containing alginate remains. Next, calcium salts are added, causing the dissolved alginate to become insoluble and drop out of solution. Finally the alginate is treated with sodium carbonate to form sodium alginate.
Chemical Properties
Sodium alginate is a polymer composed of a repeating chain of the carbohydrates D-mannuronic and L-guluronic acid. The properties of sodium alginate vary according to the length of the polymer. It is an odorless, white to yellowish brown that can look fibrous, grainy or granular or like a dry powder. Sodium alginate dissolved in water forms a thick and relatively slow-pouring liquid solution.
Food Uses
Sodium alginate is added to food as an emulsifier, a stabilizer, a thickener and a gelling ingredient. As an emulsifier, sodium alginate helps oily and watery food ingredients mix together. As a stabilizer, it is a binding agent that holds mixtures together and prevents separation. Sodium alginate absorbs water and adds thickness and body to foods without altering their taste. Finally, sodium alginate can be used to create smooth, gelled or jam-like foods or snacks.
A bizarre example of sodium alginate's power as a food additive was reported in the June 26, 2011 edition of the “Los Angeles Times” online. According to the article, Chinese manufacturers sold kits to make fake eggs by injecting sodium alginate gel into calcium carbonate shells. Sellers of the kits claimed you could make ersatz eggs for one-fourth the price of the real thing.
Medical Uses
Sodium alginate has some important medical uses. It's an ingredient in an over-the-counter remedy for acid reflux disease. A 1998 study published in "Alimentary Pharmacology and Therapeutics" compared a sodium alginate antacid with the prescription acid reflex medication cisapride. The researchers found that the sodium alginate preparation was more effective and less expensive than cisapride.
Sodium alginate can also slow the absorption of radioactive isotopes in the body. A 1991 study published in "Biomedical and Environmental Sciences" found sodium alginate could reduce the absorption rate of radioactive strontium by 78 percent.
References
- Food and Drug Administration; Code of Federal Regulations Title 21: Sec. 184.1724 Sodium Alginate; November 1983
- CyberColloids.net; Introduction to Alginate - Structure
- CyberColloids.net; Introduction to Alginate - Production
- "Los Angeles Times"; China Wrestles With Food Safety Problems; Barbara Demick; June 2011
- "Alimentary Pharmacology and Therapeutics"; Randomized, Multicentre Comparison of Sodium Alginate and Cisapride in the Symptomatic Treatment of Uncomplicated Gastro-Oesophageal Reflux; T. Poynard et al.; February 1998
- "Biomedical and Environmental Sciences"; Suppression of Radioactive Strontium Absorption by Sodium Alginate in Animals and Human Subjects; Y.F. Gong et al.; September 1991
- DidYouKnow.com; Sargasso Sea Without a Coastline
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