Water-based microwave-assisted extraction of polyphenols from Saccharina latissima: process optimization and rapid extraction kinetics

Microwave-assisted extraction (MAE) under pressurized water conditions represents an intensified solid-liquid extraction strategy for sustainable biomass valorization. However, quantitative kinetic characterization under intensified regimes remains limited. In this study, the optimization and extraction kinetics of total polyphenols from Saccharina latissima were investigated using water as the extraction solvent. Single-factor experiments and Box-Behnken response surface methodology identified extraction temperature and solvent-to-biomass ratio as the dominant parameters governing total polyphenol content (TPC), while extraction time exhibited diminishing influence at high thermal severity. The optimized conditions (196 °C, 40 mL g−1, 10 min) were experimentally validated within the predicted confidence interval. Sub-minute kinetic analysis conducted at the optimized temperature revealed that more than 90% of the equilibrium TPC was recovered within approximately 0.5 min. The extraction behavior was accurately described by a first-order approach-to-equilibrium model (R2 = 0.988; k = 4.75 min−1), indicating strongly intensified mass transfer under microwave-induced volumetric heating and pressurized hot water conditions. The extremely short characteristic extraction time suggests a shift from conventional diffusion-controlled regimes to structurally-assisted release mechanisms. Moreover, the findings provide quantitative parameters relevant for reactor sizing and residence time optimization, supporting water-based MAE as a viable and intensified unit operation for sustainable bioseparation within seaweed biorefinery systems.