Green and efficient extraction of polysaccharides from brown seaweed by adding deep eutectic solvent in subcritical water hydrolysis

Abstract Herein, deep eutectic solvent combined with subcritical water extraction of seaweed polysaccharides were investigated from Saccharina japonica. In this regard, a deep eutectic solvent was added with sufficient amount of water and it was used as an extraction medium. To optimize, a Box–Behnken design was used to study the influences of the temperature (100 °C–150 °C), pressure (10–50 bar), water content (50%–70%), and liquid/solid (L/S) ratio (30–50 mL/g). The optimal conditions were 150 °C, 19.85 bar, and 70% water content, and L/S ratio of 36.81 mL/g showed a high yield of alginate (28.12%) and fucoidan (14.93%). FTIR, TGA, and DSC measurements confirmed that the extracted polysaccharides had the features of alginate and fucoidan. 1H NMR data revealed that extracted alginate had an M/G ratio of 4.5 and η