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Carrageenans orcarrageenins (/ˌkærəˈɡiːnɪns/KAH-rə-GHEE-nihns; from Irish carraigín 'little rock') are a family of natural linearsulfatedpolysaccharides. They are extracted fromrededible seaweeds. Carrageenans are widely used in thefood 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. Carrageenans have emerged as a promising candidate intissue engineering and regenerative medicine applications as they resemble animalglycosaminoglycans (GAGs). They are used fortissue engineering, wound coverage, anddrug delivery.[1]
Carrageenans contain 15–40%ester-sulfate content, which makes themanionic polysaccharides. They can be mainly categorized into three classes based on their sulfate content. Kappa-carrageenan has one sulfate group per disaccharide, iota-carrageenan has two, and lambda-carrageenan has three.[2]
A common seaweed used for manufacturing thehydrophiliccolloids to produce carrageenan isChondrus crispus (Irish moss), which is a dark red, parsley-like alga that grows attached to rocks. Gelatinous extracts ofC. crispus have been used as food additives since approximately the fifteenth century.[3] Carrageenan is avegetarian andvegan alternative togelatin in some applications, and is used to replace gelatin in confectionery and other food.
The first industrialcommercial cultivation ofEucheuma andKappaphycus spp. for carrageenan was developed in thePhilippines. The global top producers of carrageenan are the Philippines andIndonesia.[4][5][6] Carrageenan, along withagar, is used to produce traditional jelly desserts in thePhilippines calledgulaman.[7]
Noclinical evidence establishes carrageenan as an unsafe food ingredient, mainly because its fate after digestion is inadequately determined.[8]
Carrageenans are large, highly flexible molecules that form curlinghelical structures. This gives them the ability to form a variety of differentgels at room temperature. They are widely used in the food and other industries asthickening andstabilizing agents.
All carrageenans are high-molecular-weight polysaccharides and mainly made up of alternating 3-linked β-D-galactopyranose (G-units) and 4-linked α-D-galactopyranose (D-units) or 4-linked 3,6-anhydro-α-D-galactopyranose (DA-units), forming the disaccharide repeating unit of carrageenans.[9]
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 repeatinggalactose 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 carrageenansduring their developmental history. For instance, the genusGigartina produces mainly kappa carrageenans during itsgametophytic stage, and lambda carrageenans during itssporophytic stage. 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 theEU additiveE numbers E407 or E407a when present as "processed eucheuma seaweed".[12] Technically carrageenan is considered a dietary fibre.[13][14]
In parts of Scotland and Ireland, where it is known bya 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 topanna cotta,tapioca, orblancmange.
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Although carrageenans were introduced on an industrial scale in the 1930s, they were known to be used inChina since around 600 BC (whereGigartina was used) and inIreland around 400 AD.[15][16]
Carrageenan derived fromEucheuma spp. (today one of the main cultivated sources of carrageenan), known asgusô ortambalang in theVisayan languages, has also been traditionally used as food in thePhilippines. They were first recorded in theDiccionario De La Lengua Bisaya, Hiligueina y Haraia de la isla de Panay y Sugbu y para las demas islas (c.1637) of theAugustinian missionaryAlonso de Méntrida(in Spanish). In the book, Méntrida describes gusô as being cooked until it melts, and then allowed to congeal into a sour dish.[17]
The most commonly used sources areEucheuma cottonii,Kappaphycus alvarezii, andEucheuma spinosum, which together provide about three-quarters of the world production.[citation needed] These grow from the sea surface to a depth of about 2 m (6.6 ft). 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 (2.2 lb).
After harvest, the seaweed is dried, baled, and sent to the carrageenan manufacturer. There the seaweed is ground, sifted to remove impurities such assand, and washed thoroughly. After treatment with hotalkali solution (e.g., 5–8%potassium hydroxide), thecellulose is removed from the carrageenan bycentrifugation andfiltration. The resulting carrageenan solution is then concentrated byevaporation. It is dried and ground to specification.
There are three types of industrial processing:
This is only produced fromE. cottonii orE. 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.[18]
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 drying ↓ ↓ milling milling ↓ ↓ blending blending ↓ ↓ gel refined carrageenan 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 isopropyl alcohol (propan-2-ol) or by potassium chloride.[19]
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.
There are two basic grades of carrageenan, refined (RC) and semi-refined (SRC). The latter is also known as "processedEucheuma seaweed" (PES) and "Philippine natural grade" (PNG) carrageenan.[20][21] In the European Union, refined carrageenan is designated by theE number E-407 and semi-refined carrageenan as E-407a.[12] Refined carrageenan has a 2% maximum for acid-insoluble material and is produced by alcohol precipitation or potassium chloride gel press process.[20] Semi-refined carrageenan has a much higher cellulose content[22] 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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In the U.S., carrageenan is allowed under FDA regulations[23] as a direct food additive and isgenerally regarded as safe[24] when used as an emulsifier, stabilizer, or thickener in foods, except those standardized foods that do not provide for such use. FDA reviewed carrageenan safety for infant formula.[25] TheEuropean Food Safety Authority concluded "there is no evidence of any adverse effects in humans from exposure to food-grade carrageenan, or that exposure todegraded carrageenan from use of food-grade carrageenan is occurring".[26] TheJoint FAO/WHO expert committee on food additives stated in a July 2014 review "that the use of carrageenan in infant formula or formula for special medical purposes at concentrations up to 1000 mg/L is not of concern".[27]
Although the USNational Organic Program (NOP) added carrageenan to its National List of additives allowed to be included in organic foods in 2003,[28] and reauthorized it in 2008,[29] noting it as "critical to organic production and handling operations",[30] on November 18, 2016, the NOP'sNational Organic Standards Board (NOSB) voted to recommend carrageenan be removed from the National List.[31] On April 4, 2018, theAgricultural Marketing Service (AMS) (USDA) announced the renewal of carrageenan on the National List, allowing its continued use in food products. The document states,
The NOSB recommended removing carrageenan because they determined that alternative materials, such as gellan gum, guar gum, or xanthan gum, are available for use in organic products ... AMS found sufficient evidence in public comments to the NOSB that carrageenan continues to be necessary for handling agricultural products because of the unavailability of wholly natural substitutes (§ 6517(c)(1)(ii)). Carrageenan has specific uses in an array of agricultural products, and public comments reported that potential substitutes do not adequately replicate the functions of carrageenan across the broad scope of use. Therefore, carrageenan continues to meet the OFPA criteria for inclusion on the National List.[32]
The use of carrageenan in infant formula is prohibited in the EU for precautionary reasons, but is permitted in other food items.[33] In 2018, theEuropean Food Safety Authority (EFSA) reported that safety of carrageenan in food products is based 75 mg/kg body weight per day.[8]
In the UK, theFood Standards Agency issued a product recall for sweets containing carrageenan, stating that carrageenan "is not permitted as an ingredient in jelly confectionery products as it presents a choking hazard".[34]
In a 2015 review, the Joint Expert Committee of theFood and Agriculture Organization of theUnited Nations andWorld Health Organization on Food Additives reported on the use of carrageenan ininfant formula stating that the additive was "not of concern" as food for special medical purposes at concentrations up to 1000milligrams perlitre.[35]
In 2018, carrageenan was deemed non-toxic by theEFSA under certain consumption levels (75 mg/kg of body weight per day), although further research was recommended, mainly focused on the fate of carrageenan during and after digestion, and on any subsequent metabolites.[8][36]
Research has been done into the role of carrageenan in various forms ofinflammatory bowel disease andallergic reactions,[37][38] with much of the concern centered around the specific α-D-Gal-(1→3)-D-Galglycosidic bond present in carrageenan, which interacts as anepitope withTLR4 in cultivated human epithelial cells of the mucous membrane;[36][38] this is linked toalpha-gal syndrome.[39][40] Other mechanisms of carrageenan-induced inflammation have also been proposed.[38][37][41]