| Summary: | Sulfated polysaccharide fucoidan isolated from brown algae shows a wide range of biological activities that are significantly dependent on its chemical composition, which is closely related to the applied technique and extraction parameters. Therefore, the objective of this study was to evaluate the influence of microwave assisted extraction (MAE) and pressurized liquid extraction (PLE) parameters (solvent, temperature, time, and number of cycles) on the <i>Fucus virsoides</i> and <i>Cystoseira barbata</i> polysaccharide yield (%PS) and chemical composition (total sugar, fucose, and sulfate group). The optimal MAE parameters that resulted in the highest polysaccharide extraction from <i>F. virsoides</i> and <i>C. barbata</i> were 0.1 M H<sub>2</sub>SO<sub>4</sub> for 10 min at 80 °C, while the optimal PLE parameters were 0.1 M H<sub>2</sub>SO<sub>4</sub>, for two cycles of 15 min at 140 °C. Furthermore, the %PS, chemical structure, molecular properties, and antioxidant activity of the <i>F. virsoides</i> and <i>C. barbata</i> polysaccharide extracts obtained with MAE, PLE, and conventional extraction (CE) performed under previously determinate optimal conditions were compared. PLE resulted in a significantly higher %PS from <i>F. virsoides,</i> while for <i>C. barbata</i>, a similar yield was achieved with CE and PLE, as well as CE and MAE, for both algae. Furthermore, the polysaccharides obtained using PLE had the highest polydispersity index, fucose, and sulfate group content, and the lowest uronic acid content; however their antioxidant activity was lower.
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