To describe the chemical structure of carrageenans, proposed a nomenclature including the descriptor for the monosaccharide unit and the position of the sulfate group in combination with the letter S. According to this nomenclature, a 1,3-linked β-Dgalactopyranose that is sulfated at position O-4 is for example named 'G4S' . Moreover, the structures of carrageenans are often described by using repeating disaccharide motifs (consisting of one G and one D/DA-unit). Depending on the disaccharide unit present, carrageenans are categorized into different types, which are abbreviated with Greek letters. The most commercially important types are -carrageenan (G4S-DA), -carrageenan (G4S-DA2S), and -carrageenan (G2S-D2S,6S) . Carrageenans containing a D-unit instead of a DA-unit (e. g. -carrageenan, -carrageenan, -carrageenan) are often referred to as natural precursors. The conversion into the DA-unit typically occurs under alkaline conditions or by the use of enzymes. For example, -carrageenan (G4S-D2S,6S) can be converted into -carrageenan (G4S-DA2S) .