Extraction, isolation and structural characterization of polysaccharides from a red alga Gloiopeltis furcata

Abstract

Three kinds of polysaccharides: GFW, GFH and GFA, were sequentially extracted from a red alga Gloiopeltis furcata with 25°C and 85°C water, and 60 4% NaOH water solution. Based on the defatted alga, the yields of the polysaccharide were 57.9%, 2.5% and 2.6%, respectively. Their monosaccharide compositions, average molecular weights and structural characters were determined by gas chromatography (GC), high performance liquid chromatography (HPLC), fourier transform infrared spectroscopy (FTIR) or 13C-NMR spectroscopy. The results showed that GFW, GFH and GFA were all composed of D-galactose (Gal) and 3,6-anhydro-L-galactose (AnG), and particularly GFA also contained xylose (Xyl). The average molecular weights of GFW, GFH and GFA were 22.6 kD, 26.5 kD and 49.8 kD, respectively, with the respective sulfate content 31.2%, 25.1% and 22.7%. The data of FTIR and 13C-NMR confirmed the sulfate ester location at C6 of galactose. It is concluded that all the three polysaccharides extracted from Gloiopeltis furcata were sulfated galactans, two being sulfated-agarose, and one being xylose-containing sulfated galactan.