Evaluation of the antioxidant potential of brown seaweeds extracted by different solvents and characterization of their phenolic compounds by LC-ESI-QTOF-MS/MS.

Seaweeds, serving as valuable natural sources of phenolic compounds (PCs), offer various health benefits like antioxidant, anti-inflammatory properties, and potential anticancer effects. The efficient extraction of PCs from seaweed is essential to harness their further applications. This study compares the effectiveness of different solvents (ethanol, methanol, water, acetone, and ethyl acetate) for extracting PCs from four seaweed species: Ascophyllum sp., Fucus sp., Ecklonia sp., and Sargassum sp. Among them, the ethanol extract of Sargassum sp. had the highest content of total phenolics (25.33 ± 1.45 mg GAE/g) and demonstrated potent scavenging activity against the 2,2-diphenyl-1-picrylhydrazyl radical (33.65 ± 0.03 mg TE/g) and phosphomolybdate reduction (52.98 ± 0.47 mg TE/g). Ecklonia sp. had the highest content of total flavonoids (0.40 ± 0.02 mg QE/g) in its methanol extract, whereas its ethyl acetate extract contained the highest content of total condensed tannins (8.09 ± 0.12 mg CE/g). Fucus sp. demonstrated relatively strong antioxidant activity, with methanolic extracts exhibiting a scavenging ability against 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical (54.41 ± 0.24 mg TE/g) and water extracts showing ferric-reducing antioxidant power of 36.24 ± 0.06 mg TE/g. Likewise, liquid chromatography-mass spectrometry identified 61 individual PCs, including 17 phenolic acids, 32 flavonoids, and 12 other polyphenols. Ecklonia sp., particularly in the ethanol extract, exhibited the most diverse composition. These findings underscore the importance of selecting appropriate solvents based on the specific seaweed species and desired compounds, further providing valuable guidance in the pharmaceutical, nutraceutical, and cosmetic industries. PRACTICAL APPLICATION: The PCs, which are secondary metabolites present in terrestrial plants and marine organisms, have garnered considerable attention due to their potential health advantages and diverse biological effects. Using various organic/inorganic solvents during the extraction process makes it possible to selectively isolate different types of PCs from seaweed species. The distinct polarity and solubility properties of each solvent enable the extraction of specific compounds, facilitating a comprehensive assessment of the phenolic composition found in the seaweed samples and guiding industrial production.