Over the past decade, particular attention was given to matricial polysaccharides from marine Pheophyceae and Rhodophyceae due to their biological and rheological properties. Among them, those extracted from algae belonging to Cystoseira genus have been poorly explored despite its abundance along the eastern Atlantic and Mediterranean coasts. So, the main goals of this study were the structural characterization and the evaluation of rheological and antioxidant properties of a fucoidan (CCF) and an alginate (CCSA) extracted from the Tunisian (Kerkennah, Sfax) brown seaweed Cystoseira compressa.
CCF was a sulfated (14.7%) heterogalactofucan (62.5% fucose, 24.3% galactose) composed of highly-branched α-(1,3) and α-(1,4)-linked L-Fucp as main backbone. 31.8% of O-3 and O-4 positions were ramified by monosaccharides and side chains such as terminal α-L-Fucp, terminal β-D-Galp, β-D-Galp-(1→3)-α-L-Fucp and β-D-Galp-(1→4)-α-L-Fucp. The Mw, Mn, PDI and [η] of CCF were respectively 105 KDa, 23 KDa, 4.6 and 42 mL/g. CCF solutions in water exhibited a fluid-like viscoelastic behavior with a low viscoelasticity character as influenced by temperature and monovalent salts.
CCSA, characterized by several chromatographic analyses, was composed of mannuronic (44%) and guluronic (56%) acids revealing its polyelectrolyte nature. The M/G ratio determined by 1H-NMR was close to 0.77. This alginate was constituted by 93% of homoblocks (FGG = 53% and FMM = 40%) and 6% of heteroblocks (FMG = 3% and FGM = 3%) with a high distribution of homopolymeric blocks (η= 0.13 < 1). CCSA solutions in water displayed a shear-thinning behavior, a fluid-like viscoelastic behavior with a great viscoelasticity character as influenced by temperature and adding monovalent and divalent salts.
Finally, CCF and CCSA revealed effective antioxidant activities by ferrous ion chelation, ferric ion reduction and DPPH radical scavenging, outlining their potentials as natural additives.