Structural description

Carrageenan is a generic term for several polysaccharides also extracted from red seaweeds (Rhodophyceae). Carrageenan compounds differ from agar in that they have sulfate groups (-OSO3-) in place of some hydroxyl groups. Carrageenans are water-soluble galactans extracted from some red seaweeds (mainly Chondrus, Euchema and Gigartina Genuses). They have a repeating backbone of 3-linked β-D-galactose (G-units) and 4-linked α-D-galactose (D-units), containing a varying degree of sulphate (from 20 to 50% sulfation degree). 4-linked α-D-galactose residues may also be found as 3’ and 6’ anhydro residues (DA-units).

The commercially important κ-carrageenan contains a 3,6-anhydro-D-galactopyranose (AnGalp) in place of α-D-galactopyranose, giving it gelling properties.

The addition of a 2-O-sulfo group to the  κ-carrageenan affords another commercially important carrageenan, i-carrageenan.

Carrageenan classification is based on number, position of sulfo groups and presence of 3,6-anhydro-D-galactopyranose (AnGalp) in place of α-D-galactopyranose (Nomenclature given by Knutsen et al.1994. Botanica marina, 37, 163-169).

Activities and Uses

In the food industry field, carageenan are thickening suspending, gelling and stabilizing agents (Food additive with E number 407). Antiviral (HSV, HIV), Antitumor activities. Cosmetics (anti-oxydant activity, antihyperlipidemic). Carrageenans have shown plant health activities.

κ-carrageenans have shown immunomodulation and antitumor activities (H. Yuan et al. 2006; Cancer Letters 243; 228–234).

Recommended paper: V.L. Campo et al.; Carbohydrate Polymers, 77, (2009) 167–180.