Abstract
A novel sulfated xylogalactan-rich fraction (JSP for J. adhaerens Sulfated Polysaccharide) was extracted from the red Tunisian seaweed Jania adhaerens. JSP was purified using an alcoholic precipitation process and characterized by Attenuated Total Reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), high-pressure size exclusion chromatography (HPSEC) with a multi-angle laser light scattering (MALLS), gas chromatography coupled to mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR, 1D and 2D). JSP was then evaluated regarding its physicochemical and rheological properties. Results showed that JSP was mainly composed of an agar-like xylogalactan sharing the general characteristics of corallinans. The structure of JSP was mainly composed of agaran disaccharidic repeating units (→3)-β-d-Galp-(1,4)-α-l-Galp-(1→)n and (→3)-β-d-Galp-(1,4)-3,6-α-l-AnGalp-(1→)n, mainly substituted on O-6 of (1,3)-β-d-Galp residues by β-xylosyl side chains, and less with sulfate or methoxy groups. (1,4)-α-l-Galp residues were also substituted by methoxy and/or sulfate groups in the O-2 and O-3 positions. Mass-average and number-average molecular masses (Mw) and (Mn), intrinsic viscosity ([η]) and hydrodynamic radius (Rh) for JSP were, respectively, 8.0 × 105 g/mol, 1.0 × 105 g/mol, 76 mL/g and 16.8 nm, showing a flexible random coil conformation in solution. The critical overlap concentration C* of JSP was evaluated at 7.5 g/L using the Williamson model. In the semi-diluted regime, JSP solutions displayed a shear-thinning behavior with a great viscoelasticity character influenced by temperature and monovalent salts. The flow characteristics of JSP were described by the Ostwald model.
Highlights
Water-soluble sulfated galactans are the main constituents of the non-fibrillar cell walls and intercellular matrix of most red algae (Rhodophyta) [1,2,3]
Using Fourier-transform infrared spectroscopy (FTIR), high-pressure size exclusion chromatography (HPSEC) with a multi-angle laser light scattering (MALLS), gas chromatography coupled to mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR)
Tostructure conclude, these analyses showed that JSPof presents a new and complex and complex polysaccharide compared to other xylogalactans corallinans reported in the polysaccharide structure compared to other xylogalactans of corallinans reported in the literature
Summary
Water-soluble sulfated galactans are the main constituents of the non-fibrillar cell walls and intercellular matrix of most red algae (Rhodophyta) [1,2,3]. They show a linear backbone consisting of alternating (1,4)-linked α-Gal (and/or 3,6-α-AnGal) and (1,3)-linked β-Gal units. The main backbone can be substituted by pyruvic acid ketals, sulfate, O-glycosyl and/or methyl groups and by side chains, giving rise to great structural changes along the galactan chain. These structural changes affect the physicochemical and rheological behaviors of these polymers. Seaweeds (micro- and macroalgae) are attracting growing attention as an alternative source of biofuel by converting the seaweed biomass and, in particular, the cell wall, which is rich in carbohydrates, into liquid biofuels [15]
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