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Carrageenans or carrageenins (// KARR-ə-GHEE-nənz from Irish carraigín, "little rock") are a family of linear sulphated polysaccharides that are extracted from red edible seaweeds. They are widely used in the food industry, for their gelling, thickening, and stabilizing properties. Their main application is in dairy and meat products, due to their strong binding to food proteins. There are three main varieties of carrageenan, which differ in their degree of sulphation. Kappa-carrageenan has one sulphate per disaccharide. Iota-carrageenan has two sulphates per disaccharide. Lambda carrageenan has three sulphates per disaccharide.
Gelatinous extracts of the Chondrus crispus (Irish Moss) seaweed have been used as food additives for hundreds of years. Carrageenan is a vegetarian and vegan alternative to gelatin in some applications, although it cannot replace gelatin in confectionery like jelly beans.
Carrageenan has undergone many long-term dietary studies under defined regulatory conditions en route to its current global regulatory status. While some indicate that carrageenan safely passes through rat GI tracts without adverse effect when it is a dietary ingredient, other animal dietary studies have observed colitis-like disease and tumour promotion. In the late 2000s, some scientists raised concerns about whether the amount of "degraded carrageenan" (poligeenan) in food-grade carrageenan may lead to health problems, leading to a debate in the research literature. It is yet to be determined whether such observations are pertinent to dietary safety considerations.
Europe prohibits the use of carrageenan in infant formula, organic or otherwise, for precautionary reasons, but allows it otherwise. In the U.S., it is permitted in organic foods, including juices, chocolate milk, and organic infant formula, as well as other types of foods.
Carrageenans are large, highly flexible molecules that 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.
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 α-1,3 and β-1,4 glycosidic linkages.
There are three main commercial classes of carrageenan:
The primary differences that 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". Carrageenan is mainly composed of dietary fibre, which balances the nutrition better. Technically Carrageenan is considered a Dietary Fibre.
In parts of Scotland and Ireland, where it is known by a variety of local and native names, Chondrus crispus is boiled in milk and strained, before sugar and other flavourings such as vanilla, cinnamon, brandy, or whisky are added. The end-product is a kind of jelly similar to pannacotta, tapioca, or blancmange.
Although carrageenans were introduced on an industrial scale in the 1930s, they were first used in China around 600 B.C. (where Gigartina was used) and in Ireland around 400 A.D. Carrageen gelatin can be prepared at home using the traditional recipe found in Diderot's encyclopedie and used for centuries. 5oz rinsed Irish moss is cooked with 8 quarts of water for 10 minutes, stirred as it boils. Hard water should be mixed with 1/2 oz of borax. Two quarts of cold water are rapidly added to the hot brew, and after the mixture has cooled it is strained through a cloth. It is then cooled for 24 hours and becomes gelatinous.
As of 2011[update], global sales of carageenan were estimated at $640 million. The largest producer of industrial carrageenan was the Philippines, where cultivated seaweed produces about 80% of the world supply, while China is the main exporter to global markets in the US and Europe. The most commonly used sources are E. cottonii (Kappaphycus alvarezii, K.striatum) and E. 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 it is harvested after three months or so, when each plant weighs approximately 1 kg.
The E. 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 industrial processing:
This is only performed using E. cottonii or E. spinosum. The raw weed is first sorted and crude contaminants are 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. E. 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 U.S., it simply falls under the common carrageenan specification.
cleaned and washed seaweed ↓ extraction ↓ coarse filtration → seaweed residue ↓ fine filtration → used filter aids ↓ ------------ concentration --------↓ preparation with KCl preparation with alcohol ↓ ↓ gel pressing alcohol recovery ↓ | drying | ↓ ↓ milling drying ↓ ↓ blending milling ↓ ↓ gel refined carrageenan blending ↓ refined carrageenan
The essential difference in the refining process is that the carrageenan is first dissolved and filtered to remove cell wall debris. The carrageenan is then precipitated from the clear solution either by isopropanol or by potassium chloride.
A hybrid technology in which seaweed is treated heterogeneously as in the semirefined process exists, but alcohol or high salt levels are used to inhibit dissolution. This process is often used on South American seaweeds and gives some of the cost benefits of semirefined processing, while allowing a wider range of seaweeds to be processed, however, the naturally low cellulose levels in some South American seaweeds allow them to be heterogeneously processed and still be sold under the EU refined specification.
A 2006 in vitro study and a 2007 mouse study at the National Cancer Institute in the United States suggested that carrageenans might function as a topical microbicide. A 1987 in vitro study in Spain revealed a broad spectrum antiviral activity of carrageenan.
There are indications 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 a carrageenan-based gel effectively prevented HSV-2 infection at a rate of 85% in a mouse model.
Laboratory studies have shown carrageenans inhibit HPV infection in vitro and in mouse challenge models. A substudy of a South African HIV-prevention clinical trial found a lower prevalence of high risk HPV infection in users of a carrageenan-based vaginal microbicide, Carraguard, versus placebo users at the end of the trial—prevalence of high risk HPV infection at the beginning of the trial was not ascertained.
A phase 3 clinical trial by the Population Council examined whether a carrageenan-based product 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 having used the lubricant and those not having used the lubricant. The trial also provided information about usage patterns and showed that the gel does not increase infection any more than the baseline or cause significant side-effects. As such, it is expected to be used 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 with 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.
There have been several peer-reviewed animal studies suggesting tumor promotion or initiation by carrageenan. In an industry-funded study, Cohen & Ito discuss methodological problems with four such studies, along with several evaluations of genotoxic activity, and conclude that there is no credible evidence that carrageenan contributes to tumor promotion or colon cancer. In contrast, Tobacman's review of 45 publicly funded studies concludes that "the potential role of carrageenan in the development of gastrointestinal malignancy and inflammatory bowel disease requires careful reconsideration of the advisability of its continued use as a food additive." As of 2011, Kanneganti et al. note that "the role of both CGN [carrageenan] and dCGN [degraded carrageenan] as carcinogens still remains controversial".
Studies conducted with isolated cells and human intestinal epithelial cells in tissue culture as models for in vivo conditions have suggested carrageenan may trigger a number of responses in the body that lead to inflammation of the intestines or, bind to and activate several membrane receptor signaling pathways.
Carrageenan is commonly used to induce inflammatory responses in mice. Notably, the air pouch inflammation model is based on administration of 1% carrageenan into sub-cutaneous air pouches in mice and strong inflammatory reactions are observed as early as 4 hours post administration. This in vivo inflammation model has been widely used to study the effect of anti-inflammatory compounds.
Carrageenan's function as a food additive relates to its large molecular weight (200,000 - 800,000 Da) and tight binding to food protein, but also influences carrageenan's fate as it passes through the GI tract. Oral feeding studies with laboratory animals indicate dietary carrageenan is excreted quantitatively  and is not accumulated in body organs such as the liver or colon; studies disagree with respect to whether it triggers gastrointestinal tract inflammation or contributes to tumor promotion. Long-term oral feeding studies found no adverse effects on male or female infant baboons reared from birth to 112 days of age on infant formula containing carrageenan at 5-times the concentration typically present in human infant formula as their only diet, but did observe histopathologic changes in rhesus monkey colon after drinking solution containing 1% undegraded carrageenan. Similarly, while no adverse effects were observed for multi-generations of rats fed up to 5% dietary carrageenan, or on hamsters and rats fed for a lifetime diets containing up to 5% carrageenan, administration of carrageenan to rodents in drinking water has resulted in some observations of GI-tract effects. Tight binding of carrageenan to ingested food proteins is considered less available than in drinking water for interaction with the absorptive cells of the GI tract, although some studies have linked food-grade carrageenan to gastrointestinal disease in laboratory animals, including ulcerative colitis-like disease, intestinal lesions, and ulcerations.
Carrageenan is inert to hydrolysis by intestinal enzymes in both humans and monogastric animals. Many older studies and a few recent studies have been based on the use of "degraded carrageenan," a fraction of low-molecular weight segments of the carrageenan molecular backbone called "poligeenan." To resolve this within the scientific community, the U.S. Adopted Names Council assigned the name "poligeenan" to the fragments with molecular weight of 10,000 to 20,000 Da. Approximately 8% of the fragments of food-grade carrageenan are of molecular mass less than 50,000 Da, in excess of the recommended minimum of 5% set by the European Scientific Committee on Food to ensure that the presence of poligeenan is kept to a minimum. The proportion of this 8% that consists of poligeenan is unknown.
In the U.S., carrageenan is allowed under FDA regulations as a direct food additive and is considered safe when used in the amount necessary as an emulsifier, stabilizer, or thickener in foods, except those standardized foods that do not provide for such use. FDA also reviewed carrageenan safety for infant formula. The National Organic Program (NOP) added carrageenan to the National List; reviewed and reauthorized in 2008 as "critical to organic production and handling operations". The European Food Safety Authority concluded "there is no evidence of any adverse effects in humans from exposure to food-grade carrageenan, or that exposure to degraded carrageenan from use of food-grade carrageenan is occurring", however, 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".
Environmental advocate Dr. Helen Caldicott has drawn attention to the effect of radiation effects from the Fukushima Daiichi nuclear disaster on ocean life, arguing that seaweeds come from the Pacific Ocean must be looked at carefully. Concerns include the potential presence of carcinogenic radionuclides and the degradation of carrageenan by radiation; radiation degrades carrageenan, and degraded carrageenan has been more closely associated with adverse health outcomes than undegraded carrageenan in animal studies. No studies have yet been conducted to determine whether radiation-exposed Pacific seaweeds pose a danger to human health.
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There are two basic grades of carrageenan: refined carrageenan (RC) and semi refined carrageenan (SRC). In the United States, RC and SRC are both labeled as carrageenan. In the European Union, RC is designated by the E number E-407, and SRC is E-407a. RC has a 2% maximum for acid insoluble material and is produced through an alcohol precipitation process or potassium chloride gel press process. SRC contains a much higher level of cellulosic content and is produced in a less complex process. Indonesia, The Philippines, and Chile are three main sources of raw material and extracted carrageenan.
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