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

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 H-1-NMR, C-13-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-alpha-L-galactose (3.0-34.4%) and beta-D-galactose-6-sulfate, indicating the basic funoran backbone. Variable amounts of 6-Omethyl-beta-D-galactose, 2-O-methyl-3,6-anhydro-alpha-L-galactose, alpha-L-galactose-6-sulfate, unsubstituted beta-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 H-1 and C-13 NMR resonances of the beta-D-galactose-6-sulfate - 2-O-methyl-3,6-anhydro-alpha-L-galactose diad (G6S-LA2M) for the first time. (C) 2014 Elsevier Ltd. All rights reserved.