Carrageenan

• USP–NFCarrageenan

Chondrus extract; Gelcarin; Genu; Irish moss extract; Viscarin; E407

Sulfated galactan: potassium, sodium, calcium and magnesium salts of sulfate esters of galactose and 3,6-anhydrogalactose copolymers · [9000-07-1]

Polymer, mixture or material of variable composition — no single molecular formula applies.

Gelling agent, viscosity modifier

Typical concentrations: — · Dosage forms: Liquid, Semi-solid

Used as a gelling, thickening, suspending and stabilising agent in oral suspensions, emulsions, gels, toothpastes and topical products, and in foods. Iota-carrageenan, usually combined with starch, is used to make non-animal soft-capsule shells, and carrageenans have been investigated in controlled-release matrices and as tablet excipients.

A yellowish, tan or white, coarse to fine powder that is practically odourless and has a mucilaginous taste.

Main types

kappa (firm, brittle gels with potassium ions), iota (elastic gels with calcium ions) and lambda (non-gelling, thickening)

Ester sulfate content

roughly 25% (kappa), 32% (iota) and 35% (lambda)

Solubility

lambda and the sodium salts dissolve in cold water; kappa and iota (potassium and calcium salts) need hot water and gel on cooling; insoluble in ethanol

Gel behaviour

kappa and iota gels are thermoreversible

The dry powder is stable. Solutions lose viscosity through acid hydrolysis, which is fastest at low pH and high temperature, so prolonged heating below about pH 4–5 should be avoided. Aqueous preparations need a preservative. Store in a cool, dry place in a well-closed container.

As a strongly anionic polymer it can interact with cationic drugs and cationic surfactants, forming precipitates. It also interacts with proteins; kappa-carrageenan reacts with casein in milk, an effect exploited in dairy foods.

Extracted from red seaweeds (Rhodophyceae) such as Chondrus crispus, Kappaphycus and Eucheuma species with hot alkaline water; the extract is filtered and the carrageenan recovered by alcohol precipitation or by gelling with potassium chloride, then dried and milled. Semi-refined material (processed Eucheuma seaweed, E407a) is made without dissolving the polysaccharide.

Food-grade, high-molecular-weight carrageenan is poorly absorbed and of low oral toxicity. Degraded carrageenan (poligeenan), of low molecular weight, causes intestinal ulceration in animals and is not permitted as an additive. EFSA's 2018 re-evaluation set a temporary group ADI of 75 mg/kg body weight per day for E407 and E407a.

Observe normal precautions for the quantity handled. Avoid inhaling the dust; eye protection and a dust mask are recommended.

Accepted as a food additive in Europe (E407; processed Eucheuma seaweed E407a) and evaluated by JECFA and EFSA. Used in oral and topical medicines licensed in Europe.

Agar; alginic acid; ceratonia; sodium alginate; xanthan gum.

The type of carrageenan and the cations present largely determine its behaviour, so the type should be specified. Kappa-carrageenan gels synergistically with locust bean gum, giving more elastic gels with less syneresis.