Structural and compositional characteristics of gelling galactan from the red alga Ahnfeltia tobuchiensis (Ahnfeltiales, the Sea of Japan)

The composition and structure of a sulfated polysaccharide from Ahnfeltia tobuchiensis, a red seaweed of Kuril Islands and Japan, were investigated. Samples of the galactan were characterized by 13C NMR and FTIR spectroscopy and chemical analysis in comparison with well-known commercial agarose preparations. The main components of the polysaccharide from A. tobuchiensis were 3,6-anhydro-l-galactose (38±4.5%) and galactose. Methoxy groups (2.2%) of the galactan are located in the position 2 of the anhydrogalactose residues. The galactan proved to be a high-sulfated agarose. Sulfur content of this polysaccharide is 0.2–0.3%, and sulfate groups may be removed by alkali treatment to a limited extent only. The precision of quantification and possibilities of analytical methods used are discussed.