Funorans from Gloiopeltis species. Part I. Extraction and structural characteristics

Abstract

The structure and composition of the polysaccharide fractions from the main species of the red algal genus Gloiopeltis – G. furcata, G. tenax and G. complanata, isolated by the successive cold and hot water extraction processes were comparatively investigated. The galactan samples were characterized by 1H-NMR, 13C-NMR, FTIR and FT-Raman spectroscopy, ICP-OES, size exclusion and gas chromatography methods. The basic components of the Gloiopeltis polysaccharides are 3,6-anhydro-α-l-galactose (3.0–34.4%) and β-d-galactose-6-sulfate, indicating the basic funoran backbone. Variable amounts of 6-O-methyl-β-d-galactose, 2-O-methyl-3,6-anhydro-α-l-galactose, α-l-galactose-6-sulfate, unsubstituted β-d-galactose and xylose (0.2–2.0%) are found to be present in all of the Gloiopeltis species. The sulfur content of the funorans isolated by hot water extraction process is 4.7–7.0%, notable quantity of uronic acids (up to 4.9%) and acetylated residues are present in the cold water extracted funoran preparations. The chemically heterogeneous Gloiopeltis polysaccharides are characterized by very high polydispersities. There is a slight dependency of the chemical composition of G. complanata funorans on the life-history stage of the alga. With the aid of 2D NMR techniques it was possible to assign the 1H and 13C NMR resonances of the β-d-galactose-6-sulfate – 2-O-methyl-3,6-anhydro-α-l-galactose diad (G6S-LA2M) for the first time.