Carrageenan

Carrageenans or carrageenins (Template:Pron-en, with a hard g) are a family of linear sulfated polysaccharides which are extracted from red seaweeds.

Gelatinous extracts of the Chondrus crispus seaweed have been used as food additives for hundreds of years. Carrageenan is a vegetarian and vegan alternative to gelatin.

Properties

The molecular structure of different types of carrageenan.

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.

All carrageenans are high molecular weight polysaccharides made up of repeating galactose units and 3,6 anhydrogalactose (3,6-AG), both sulfated and nonsulfated. The units are joined by alternating alpha 1-3 and beta 1-4 glycosidic linkages.

There are three main commercial classes of carrageenan:

• Kappa: strong, rigid gels. Gels with potassium ions, reacts with dairy proteins. Mainly from Eucheuma cottonii.
• Iota: soft gels. Gels with calcium ions. Produced mainly from Eucheuma spinosum
• Lambda: Does not gel, used to thicken dairy products. The most common source is Gigartina from South America.

The primary differences which influence the properties of kappa, iota and lambda carrageenan are the number and position of the ester sulfate groups on the repeating galactose units. Higher levels of ester sulfate lower the solubility temperature of the carrageenan and produce lower strength gels, or contribute to gel inhibition (lambda carrageenan).

Many red algal species produce different types of carrageenans during their developmental history. For instance, the genus 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", and is commonly used as an emulsifier. When iota carrageenan is combined with Sodium stearoyl lactylate (SSL) a synergistic effect is created, allowing for stabilizing/emulsifying that is not obtained with any other type of carrageenan (kappa/lambda) or with other emulsifiers (monodiglycerides, etc). Sodium stearoyl lactylate combined with iota carrageenan is capable of producing emulsions under both hot and cold conditions using either vegetable or animal fat.

Production

Although carrageenans were introduced on an industrial scale in the 1930s, they were first used in China around 600 BC (where Gigartina was used) and in Ireland around 400 AD.

The largest producer in contemporary times 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 from the sea surface to a depth of 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.

There are three types of processing:

Semi refined

This is only performed using Eucheuma cottonii or Eucheuma spinosum. The raw weed is first sorted and crude contaminants removed by hand. The weed is then washed to remove salt and sand, and then cooked in hot alkali to increase the gel strength. The cooked weed is washed, dried and milled. Eucheuma spinosum undergoes a much milder cooking cycle as it dissolves quite readily. The product is called semi refined carrageenan, Philippines natural grade or, in the USA, it simply falls under the common carrageenan specification.

Refined

The essential difference in the refining process is that the carrageenan is dissolved and filtered to remove cell wall debris. The clear solution is then precipitated either by alcohol or by potassium chloride.

Mixed processing

A hybrid technology exists where weed is treated heterogeneously as in the semi refined process but alcohol or high salt levels are used to inhibit dissolution. This process is often used on South American weeds and gives some of the cost benefits of semi refined processing, while allowing a wider ranges of weeds to be processed. Oddly the naturally low cellulose levels in some South American weeds allows them to be heterogeneously processed and still be sold under the EU refined specification.

Uses

Personal lubricant made from carrageenan.

• Desserts, ice cream, cream, milk shakes, sweetened condensed milks, sauces: gel to increase viscosity
• Beer: clarifier to remove haze-causing proteins
• Pâtés and processed meat: Substitute fat to increase water retention and increase volume
• Toothpaste: stabilizer to prevent constituents separating
• Fruit Gushers: ingredient in the encapsulated gel.
• Fire fighting foam: thickener to cause foam to become sticky
• Shampoo and cosmetic creams: thickener
• Air freshener gels
• Marbling: the ancient art of paper and fabric marbling uses a carrageenan mixture to float paints or inks upon; the paper or fabric is then laid on it, absorbing the colors.
• Shoe polish: gel to increase viscosity
• Biotechnology: gel to immobilize cells/enzymes
• Pharmaceuticals: used as an inactive excipient in pills/tablets
• Carrageenan: used to thicken skim milk, in an attempt to emulate the consistency of whole milk. This usage did not become popular. It is used in some brands of soy milk
• Diet sodas
• Soy milk
• Pet food
• Alien saliva (movie effects).
• Personal lubricants
• Lambda carrageenan is used in animal models of inflammation used to test analgesics, because dilute carrageenan solution (1–2%) injected subcutaneously causes swelling and pain.
• Shaving ham sold at restaurants and commercial delis.

Sexual lubricant and microbicide

Studies at the Laboratory of Cellular Oncology, National Cancer Institute, Bethesda, Maryland, United States of America, suggest that carrageenans might function as a topical microbicide.

HSV

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. Research has shown that a carrageenan-based gel effectively prevented HSV-2 infection at a rate of 85% in a mouse model. Some personal and condom lubricants are already made with carrageenan, and several of these products (such as Divine) were found to be potent HPV inhibitors in the study (though others that listed carrageenan in their ingredients were not). See Herpes simplex: Polysaccharides

HPV

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, and stated "We have no idea whether this is valid in humans". (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.

HIV

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. The trial did provide information about usage patterns, however, and showed that the gel is safe at least—not increasing infection any more than the baseline or causing significant side effects. As such, they expect to use it as a stable delivery vehicle for experimental antiretrovirals in future studies.

Concurrent studies in macaques found the same Carrageenan gels used in clinical trials to be effective against SIV challenge. This was in direct contrast of in vitro findings, where the compound was found to enhance HIV and SIV infections in various assays. Although compliance was believed to be one issue in clinical versus animal trials, the high viscosity and controlled nature of animal-viral inoculations (atraumatic introduction of virus using a French Catheter) may be why the latter animal study observed a positive outcome.

Health concerns

The Joint FAO/WHO expert committee on food additives states "that based on the information available, it is inadvisable to use carrageenan or processed eucheuma seaweed in infant formulas". There is evidence from studies performed on rats, guinea pigs and monkeys which indicates that degraded carrageenan (poligeenan) may cause ulcerations in the gastro-intestinal tract and gastro-intestinal cancer. Poligeenan is produced from carrageenan subjected to high temperatures and acidity. The average carrageenan molecule weighs over 100,000 Da while poligeenans have a molecular weight of less than 50,000 Da. A scientific committee working on behalf of the European Commission has recommended that the amount of degraded carrageenan be limited to a maximum of 5% (which is the limit of detection) of total carrageenan mass. Upon testing samples of foods containing high molecular weight carrageens, researchers found no poligeenan.

A recent publication indicates that carrageenan induces inflammation in human intestinal epithelial cells in tissue culture through a BCL10-mediated pathway that leads to activation of NFkappaB and IL-8. Carrageenan may be immunogenic due to its unusual alpha-1,3-galactosidic link that is part of its disaccharide unit structure. Consumption of carrageenan may have a role in intestinal inflammation and possibly inflammatory bowel disease, since BCL10 resembles NOD2, mutations of which are associated with genetic proclivity to Crohn's Disease.

Carrageenan is reported to interfere with macrophage activity.

See also

• Agar
• List of food additives