Phytochemical Constituents, Antioxidant and Antimicrobial Activities of Red Seaweed Corallina elongata (Syn. Ellisolandia elongata) from the Mediterranean Sea (Algeria)

In recent years, seaweeds have garnered significant attention due to their chemical and bioactive properties, presenting an avenue for the discovery of novel molecules with valuable applications. Among the major metabolites of seaweeds are phenolic compounds, which exhibit the greatest structural diversity. This study aimed to assess the phytochemical profile, antioxidant and antimicrobial activities of various solvent (hexane, chloroform, methanol and water) extracts of the red seaweed Corallina elongata, sourced from the Algerian West Coast. The phytoconstituents of the methanol extract were identified by high-pressure liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS-MS), followed by quantitative evaluation of the total phenolic, flavonoid, and condensed tannin contents. Antioxidant activity was assessed using 2,2-Diphenyl-1-picrylhydrazyl (DPPH) scavenging, 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) scavenging, ferric reducing antioxidant power (FRAP), and phenanthroline assays. The antimicrobial potential was assessed using the disc diffusion method. HPLC-ESI-MS-MS analysis identified 21 compounds, with p-hydroxy coumaric acid as the major compound. The methanol extract displayed the highest phenolic content (142.44 µg GAE/mg extract), while the aqueous extract had the highest flavonoid and condensed tannin contents (23.32 µg QE/mg extract and 20.00 mg CE/g extract, respectively). The aqueous extract exhibited superior antioxidant activity, with IC₅₀ values of 148.15, 27.01, and 45.85 µg/mL for DPPH, ABTS, and phenanthroline assays, respectively. Both the aqueous and methanol extracts demonstrated promising antibacterial activity against all tested bacterial strains, with inhibition zones ranging from 8.83 to 20.66 mm. Overall, the aqueous and methanol seaweed extracts proved to be the most effective, highlighting their potential as sources of bioactive compounds.