Optimization of extraction of phenolic compounds from the brown seaweed Fucus spiralis using Natural Deep Eutectic Solvents

Brown seaweeds (Phaeophyceae) have received considerable attention as a rich natural source of bioactive compounds including polysaccharides, vitamins, carotenoids and polyphenols. The phenolic composition of these seaweeds is characterised by the prevalence of phlorotannins, which are oligomers of phloroglucinol recognised for their diverse bioactivities, including antioxidant properties. The present study aimed at evaluating the effectiveness of different natural deep eutectic solvents (NADES) on the extraction of phenolic compounds from spiral wrack, Fucus spiralis, and its antioxidant properties. Firstly, using ultrasound-assisted extraction (UAE), we compared the extraction capacity of different NADES with those of conventional solvents. The results obtained demonstrated that extracts prepared with NADES (glycerol:urea; 1:1, and glucose: lactic acid; 1:5) exhibited significantly higher total phenolic contents in comparison with extracts with conventional solvents. Subsequently, an attempt was made to optimize the ultrasonic extraction of phenolic compounds using a Box-Behnken design, with total phenolic content, as well as the extracts’ antioxidant activity (by different chemical assays), designated as the response variables. The optimization process was conducted with three key factors in mind: extraction temperature (ranging from 20 to 50 °C), extraction time (ranging from 30 to 120 minutes), and liquid-to-solid ratio (ranging from 5 to 55 mg mL-1). Highest phenolic content was achieved at the highest temperature, with the longest extraction time, and an intermediate liquid-to-solid ratio.The experimental findings substantiate the hypothesis that the integration of UAE and NADES can serve as a viable substitute for conventional organic solvents, thereby facilitating a more sustainable extraction of bioactive compounds from seaweed.