Rheological investigations of water-soluble polysaccharides from the Tunisian brown seaweed Cystoseira compressa

Abstract Rheological characteristics of a sodium alginate and a fucoidan extracted from the brown seaweed Cystoseira compressa harvested from Kerkennah island (Sfax, Tunisia) were investigated. Steady-shear flow and dynamical viscoelasticity were evaluated to describe physicochemical properties of the GulA-rich alginate (ManA/GulA, M/G = 0.77) and highly-ramified fucoidan in semi-diluted media depending on polymer concentration, shear rate, temperature, added mono- (KCl and NaCl) and divalent (CaCl2) salts. Alginate solutions exhibited shear-thinning behavior, with a temperature-dependent behavior highly correlated to the power-law model and the Arrhenius relationship. The results showed strong thixotropic and polyelectrolyte properties, influenced by addition of monovalent and divalent cations. The dynamic rheological characteristics showed a fluid-like viscoelastic behavior (tan δ > 1) whereas the critical overlap concentration C* and specific polymer constant ks were respectively 11 g.L−1 and 4.4 using Williamson model. Fucoidan solutions displayed a shear-thinning behavior with a low viscoelasticity character influenced by temperature and monovalent salts. The flow and viscoelastic characteristics of polysaccharides were described by the Ostwald model.