Structural characterization and antioxidant activity of water-soluble polysaccharides from the Tunisian brown seaweed Cystoseira compressa

A fucoidan (CCF) and a sodium alginate (CCSA) were extracted and purified from the Tunisian brown seaweed Cystoseira compressa. CCF was a highly sulfated heterogalactofucan composed of alpha-(1 -> 3), alpha-(1 -> 4)-linked L-Fucp as main backbone which could be highly branched (31.84%) at O-3 and O-4 positions of alpha-(1 -> 4)-L-Fucp and alpha-(1 -> 3)-L-Fucp by terminal monosaccharides and side chains such as terminal alpha-L-Fucp, terminal ss-D-Galp, ss-D-Galp-(1 -> 3)-alpha-L-Fucp and ss-D-Galp-(1 -> 4)-alpha-L-Fucp. The ratio of alpha-(1 -> 3)/alpha-(1 -> 4) linkages was estimated at 3.86:1. CCSA was characterized by HPAEC-PAD, GC/MS-EI, ATR-FTIR, and H-1-NMR. The M/G ratio was M/G = 0.77, indicating that CCSA respectively contained 44% and 56% of mannuronic and guluronic acids. The values of F-GG, F-MM, F-GM (or F-MG) blocks as well as the parameter. were estimated. The two polysaccharides exhibited effective antioxidant activities by ferrous ion chelation, ferric ion reduction and DPPH radical-scavenging, outlining their potentials as natural additives.