Extraction and structural characterization of the polysaccharide fraction of Launaea acanthodes gum

Abstract

In this work a physico-chemical characterization of the polysaccharide fraction of the exudates of Launaea acanthodes, a common medicinal species in central regions of Iran, was performed. The extraction of the polysaccharide fraction of the exudates was described. The structure characterization of the polysaccharide was performed with mono and bi-dimensional NMR spectroscopy techniques, which allowed the chemical composition and the relative monomers abundance of the extracted fraction to be estimated. The constituent monosaccharides were predominantly galactose, rhamnose, arabinose and galacturonic acid residues. Interchain association phenomena in the main arabinogalactans component (Mw = 33.550 Da) were evidenced both from high-performance size-exclusion chromatography (HP-SEC–TDA), and by intrinsic viscosity ([ η] 0 = 0.323 dl g −1 in water and [ η] 0 = 0.115 dl g −1 in NaNO 3 0.1 M at 20 °C) measurement and the Huggings coefficient λ. Due to the formation of hyperentanglements, a unique function of C[ η] 0 cannot be defined. The technological consequence was that once structured, the polysaccharide network did not express a sufficient degree in polymer orientation and therefore cast films showed weak mechanical properties.