Characterization and in vitro assessment of the antioxidant and anti-inflammatory activities of water-soluble polysaccharides isolated from the brown algae Cystoseira amentacea from the Mediterranean coasts

Polysaccharides from marine macroalgae are biopolymers with several biological and functional properties, justifying their great interest in the food and pharmaceutical industries. In this study, polysaccharides were extracted from the brown seaweed Cystoseira amentacea, harvested on the Algerian coast. Their contents of total sugars, proteins, and polyphenols are assessed by colorimetric methods. FTIR-ATR, NMR, and GCMS-MS were used to characterize their structural and functional properties. Additionally, the antioxidant and anti-inflammatory activities of these polysaccharides were evaluated in vitro. The results show that the polysaccharides are mainly constituted of total sugars (84.25 ± 1.84 %), and glucose is the most prevalent monosaccharide in their composition, followed by rhamnose and galactose, in addition to other minor sugars, including fucose. The FTIR-ATR analysis confirmed the presence of sulfur in the polysaccharide structure. On the other hand, these heteropolysaccharides have exhibited considerable antioxidant activity, revealed by their DPPH free radical scavenging and iron reduction abilities, whose IC₅₀ were evaluated at 446.00 ± 1.41 and 1142.33 ± 1.44 μg/mL, respectively. In addition, inhibition of the protein denaturation and antiproteinase activity tests highlighted the appreciable anti-inflammatory effect of the algal polysaccharides. Therefore, they can be used as natural antioxidants and serve to develop new anti-inflammatory drugs with less harmful effects on human health and the environment.