Bioactive Polysaccharides from Djiboutian Brown Algae: Antioxidant and Anti-Aging Potential for Cosmetic Applications

Brown macroalgae are a valuable source of bioactive polysaccharides, particularly alginates and fucoidans, with significant potential for cosmetic and pharmaceutical applications. In this study, polysaccharides were extracted from four species (Padina pavonica, Sargassum ilicifolium, S. latifolium, and Turbinaria decurrens) collected along the Djibouti coastline. Structural characterization by FT-IR and 1H-NMR revealed pronounced interspecific variability. Alginates displayed distinct mannuronate/guluronate (M/G) ratios, with Sargassum latifolium showing the highest and T. decurrens the lowest, reflecting differences in polymer composition and structural flexibility. Fucoidan spectra exhibited characteristic sulfate bands at 1217–1220 and 840 cm−1, with lower transmission values for T. decurrens indicating a relatively higher degree of sulfation. Biological assays demonstrated that alginate extracts exhibited moderate antioxidant activity, whereas fucoidans showed significantly stronger radical scavenging (DPPH) and ferric reducing (FRAP) capacities, in some cases comparable to vitamin C. Fucoidans also displayed potent inhibition of skin-aging enzymes, with elastase inhibition reaching 62.1% for P. pavonica and tyrosinase inhibition peaking at 63% for S. ilicifolium at 0.5 mg/mL. These results highlight the critical role of structural features, particularly sulfation patterns, in determining biological activity. Overall, Djiboutian brown algal polysaccharides combine antioxidant and enzyme inhibitory properties, confirming their potential as multifunctional and sustainable marine-derived ingredients for cosmetic formulations.