Functionality-Driven Optimization of Green Ultrasound-Assisted Extraction of Antioxidant Compounds from Edible Brown Algae

The extraction of antioxidant compounds from brown macroalgae is of growing industrial interest; however, the weak correlation often observed between polyphenol content and antioxidant activity challenges the conventional strategy of optimizing only extraction yield. This study introduces, for the first time in brown macroalgae, a functionality-driven optimization approach in which ultrasound-assisted extraction (UAE) conditions are optimized based on antioxidant activity as the primary response variable, rather than compound concentration. A green UAE process was developed and optimized for four edible brown algae (<i>Himanthalia elongata</i>, <i>Eisenia bicyclis</i>, <i>Sargassum fusiforme</i>, and <i>Laminaria ochroleuca</i>), considering algae amount, solvent type and concentration, extraction time, ultrasound power, and temperature. The optimized extracts achieved 69.17-94.68% DPPH inhibition, together with high antioxidant capacity supported by ORAC (18.63-491.30 μmol TE g^-1 DW) and FRAP (1.24-87.65 µmol Fe⁺² g^-¹ DW) values, identifying <i>E. bicyclis</i> and <i>H. elongata</i> as the most promising species. Chromatographic analyses confirmed the presence of phlorotannins and carotenoid pigments such as fucoxanthin as the main contributors to antioxidant activity. Overall, this work validates a functionality-driven UAE optimization strategy for efficiently maximizing antioxidant activity in brown algal extracts.