Carrageenans or carrageenins are a family of linear sulphated polysaccharides extracted from red seaweeds. The name is derived from a type of seaweed that is abundant along the Irish coastline. Gelatinous extracts of the Chondrus crispus seaweed have been used as food additives for hundreds of years, though analysis of carrageenan safety as an additive continues.


Carrageenans are large, highly flexible molecules which curl forming helical structures. This gives them the ability to form a variety of different gels at room temperature. They are widely used in the food and other industries as thickening and stabilizing agents. A particular advantage is that they are pseudoplastic - they thin under shear stress and recover their viscosity once the stress is removed. This means that they are easy to pump but stiffen again afterwards.

There are three main commercial classes of carrageenan:

Many red algal species produce different types of carrageenans during their developmental history. For instance, the genera Gigartina produces mainly Kappa carrageenans during its gametophytic stage, and Lambda carrageenans during its sporophytic stage. See Alternation of generations.

All are soluble in hot water, but in cold water only the Lambda form (and the sodium salts of the other two) are soluble.

When used in food products, carrageenan has the EU additive E-number E407 or E407a when present as "Processed eucheuma seaweed". Although introduced on an industrial scale in the 1930s, the first use was in China around 600 BC (where Gigartina was used) and in Ireland around 400 AD.

The largest producer is the Philippines, where cultivated seaweed produces about 80% of the world supply. The most commonly used are Cottonii (Kappaphycus alvarezii, K.striatum) and Spinosum (Eucheuma denticulatum), which together provide about three quarters of the World production. These grow at sea level down to about 2 metres. The seaweed is normally grown on nylon lines strung between bamboo floats and harvested after three months or so when each plant weighs around 1 kg.

The Cottonii variety has been reclassified as Kappaphycus cottonii by Maxwell Doty (1988), thereby introducing the genus Kappaphycus, on the basis of the phycocolloids produced (namely kappa carrageenan).

After harvest, the seaweed is dried, baled, and sent to the carrageenan manufacturer. There the seaweed is ground, sifted to remove impurities such as sand, and washed thoroughly. After treatment with hot alkali solution (e.g. 5-8% potassium hydroxide), the cellulose is removed from the carrageenan by centrifugation and filtration. The resulting carrageenan solution is then concentrated by evaporation. It is dried and ground to specification.


Sexual lubricant and microbicide

Laboratory studies suggest that carrageenans might function as topical microbicides, blocking sexually transmitted viruses such as HPV and herpes, though not HIV.


There are indications that a carrageenan-based gel may offer some protection against HSV-2 transmission by binding to the receptors on the herpes virus thus preventing the virus from binding to cells. Researchers have shown that a carrageenan-based gel effectively prevented HSV-2 infection at a rate of 85% in a mouse model. See


A study published in August 2006 found it potentially a thousand times as effective against HPV (measuring in vitro infectivity of pseudoviruses, which are believed to mimic the activity of actual viruses). If effective, its cost compared to HPV vaccines and its ability to target any strain of the virus would make it an attractive prevention measure against cervical cancer, especially in developing countries. Some personal and condom lubricants are already made with carrageenan, and several of these products (such as Bioglide and Divine) were found to be potent HPV inhibitors in the study (though others that listed carrageenan in their ingredients were not).

Although the researchers are optimistic and show that the products "block HPV infectivity in vitro, even when diluted a million-fold", they emphasize that "it would be inappropriate to recommend currently available products for use as topical microbicides" until further human tests are complete. (By comparison, similarly optimistic results were expected for HIV prevention by cellulose sulfate gels, based on early tests, but the clinical trials had to be halted when the gel was found to increase incidence of HIV infection.)

The researchers then tested HPV infectivity in mice. This study, released in July 2007, also found promising results, preventing infection in vivo by HPV-16 pseudoviruses even in the presence of nonoxynol-9, which was shown to greatly increase infection when used alone. The results for the carrageenan tests (including those with Divine and Bioglide commercial lubricants) showed no detectable infection, while the viscous control gel and N-9 gels did.

While effectiveness trials have not been completed and side effects have not been ruled out, companies are already planning to capitalize on the discovery, such as Dreamspan naming their lubricant Carrageenan after its principal ingredient.An All Natural Anti Viral Red Marine Algae Sex Gel


A phase 3 clinical trial by Population Council examined whether a carrageenan-based product known as Carraguard was effective as a topical microbicide for blocking HIV infection in women. The trial ran from 2004 to 2007, with more than 4,000 South African women completing the study, but found no statistical difference in infection between those who used the lubricant and those who did not.

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