STRUCTURE OF CARRAGEENAN                                                                              

Three distinct types of carrageenan are recognized commercially: kappa, iota and lambda. Each is a linear polymer with a disaccharide repeating unit consisting of sugar residues linked alternately through the C3 and C4 positions. The sugar residues are D-galactose and 3,6-anhydro-D-galactose. Sulfate ester groups are located in various positions on one or both residues of the repeating unit. The idealized structures are shown below. It can be seen that the two gel-forming carrageenan molecules, kappa and iota, contain 3,6-anhydro-D-galactose as the 1,4-linked residue and have a buckled shape. The lambda carrageenan molecule is more extended.

The sulfate groups are associated with metal cations, such as sodium, potassium and calcium. Their relative proportions determine whether or not the carrageenan will dissolve in a particular medium at a certain temperature. Sodium salts of carrageenan are soluble in cold water.

Kappa carrageenan interacts with locust bean gum (for example, GENUGUM^® RL-200Z). In combination, they produce gels which are stronger, more elastic and cohesive and less prone to syneresis than gels made with kappa carrageenan alone.

Carrageenan is stable under neutral and alkaline conditions.

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