Bioactive compounds identification, antioxidant and antibacterial activities of Algerian marine algae extracts

Background: The marine algae produce bioactive compounds, including polyphenols. They have antioxidant, antibacterial, immune regulation and other biological activities. The aim of this study was to examine the antibacterial and antioxidant activities of extracts of five marine algae species: Cystoseira humilis, Halopteris scoparia, Pavonica padina, Sargassum vulgare and Rhodomela confervoides of Bejaia’s coast (northern Algeria). Methods: Phenolic content of the five marine algae was assessed using folin ciocalteu method and then characterized by HPLC-DAD and HPLC-ESI-QTOF-MS analyses. The antioxidant activity was evaluated by DPPH•, ABTS•+, NO• radical scavenging and FRAP assays. For the screening of the antibacterial activity, six strains were tested using three different methods: agar disc diffusion, agar well diffusion and spot methods. The minimum inhibitory concentrations (MICs) were also determined. Results: Protocatechuic acid was the phenolic compound identified in all the studied seaweeds, while Padina pavonica was the species where more phenolic compounds were identified (phloroglucinol, gallic acid, ferulic acid and syringic acid). Cystoseira humilis showed the highest antioxidant activity (DPPH•: 2237.50  148.34 µM TE/100 g dw, ABTS•+: 1992.50  165.97 µM TE/100 g dw, NO•: 2559.58  42.08 µM TE/100 g dw, FRAP: 2081.20 ± 115.29 µM TE/100 g dw), which was also the richest in phenolic compounds (4.63 ± 0.23 mg PhlE/g dw). Rodomela confervoides showed an important activity against all the bacterial strains tested with the greatest diameter of inhibition zone (18 mm) against E. coli with a MIC equal to 20 mg/mL. The extract of Padina pavonica showed a moderate activity (13.5 mm) against P. aeruginosa with a MIC ≤ 10 mg/mL and a MBC > 10 mg/mL. Conclusion: The studied marine algae showed antioxidant and antibacterial activities. So, they can be developed for their applications in medicine, food production and cosmetic industry.