Ionic Liquids or Eutectic Solvents: Which Is the Best for Extracting Phenolic Compounds from Macroalgae?

Abstract The increased biomass of invasive macroalga species (e.g., Sargassum muticum) is a valuable source of phenolic compounds. This study presents the extraction of these compounds using ionic liquids (ILs) and eutectic solvents (ESs) and, more importantly, addresses the broader question of which solvents may be most suitable for extracting valuable compounds from biomass. Extracts were obtained using maceration and microwave-assisted extraction. The total phenolic content, total flavonoid content, and antioxidant activity of the extracts were determined. The composition of selected extracts was characterized by LC–MS. The results showed that the choline-salicylate-based extract afforded the highest concentrations of compounds and the best antioxidant properties. As expected, depending on whether ESs or ILs with “identical structures” were used for extraction, the compositions of the extracts were different. The environmental impact of the solvents and the extracts was evaluated. The extracts were classified as “practically nontoxic” or “relatively harmless” toward Artemia franciscana and Daphnia magna. Phytotoxicity assays toward white mustard indicated “no toxicity”, “low toxicity”, or “moderate toxicity”. These findings indicate that ecotoxicity depended on the extract composition and the solvent. Collectively, these findings highlight the critical role of solvent design in enabling efficient, selective, and environmentally responsible extraction of bioactive compounds from macroalgae.