The system of galactans of the red seaweed, Kappaphycus alvarezii, with emphasis on its minor constituents Original Research Article

The galactans extracted with hot water from Kappaphycus alvarezii, after previous extraction at room temperature, are mainly composed of κ-carrageenans (∼74%) and μ-carrageenans (∼3%). However, a significant percentage of these galactans (at least 14%) is composed of sulfated agarans and, possibly, agaran-type sulfated dl-hybrid galactans. These agarans are partially substituted on C-2 or C-4 or disubstituted on both positions of the β-d-galactose units and on C-3 or C-2 and C-3 of the α-l-galactose residues with sulfate groups or single stubs of β-d-xylopyranose, d-glucopyranose, and galactose or with d-glucopyranosyl-(1→4)-d-glucopyranose side chains. Significant quantities of 2-O-methyl- and 3-O-methyl-l-galactose units are also present. A great tendency to retain Ca2+ and Mg2+, in spite of massive treatments with Na+ and K+ salts, was observed. The complexation between agarans and agarans–κ-carrageenans through divalent cations and the possible zipper-type carbohydrate–carbohydrate interactions would be two complementary mechanisms of interactions.