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

The galactans extracted with hot water from Kappaphycus alvarezii, after previous extraction at room temperature, are mainly composed of j-carrageenans (~74%) and l-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 b-D-galactose units and on C-3 or C-2 and C-3 of the a-L-galactose residues with sulfate groups or single stubs of b-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–j-carrageenans through divalent cations and the possible zipper-type carbohydrate–carbohydrate interactions would be two complementary mechanisms of interactions.