Ultrasound-assisted extraction of phlorotannins and polysaccharides from Silvetia compressa (Phaeophyceae)

Silvetia compressa is a brown seaweed native to the coast of Baja California, Mexico. It is a rich source of phlorotannins and polysaccharides, two compound families with important nutraceutical applications. Optimal conditions for obtaining highly concentrated phlorotannin and polysaccharide extracts from S. compressa were determined using Box-Behnken experimental design combined with response surface methodology (RSM). The effect of extraction temperature (X1: 50–65 °C), ultrasound power density (X2: 1.2–3.8 W cL−1), solvent/seaweed ratio (X3: 10–30 mL g−1 seaweed meal), and ethanol concentration (X4: 25–100% ethanol in water) on phlorotannin and polysaccharide yield was explored. Experimental results were fitted to a second-degree polynomial model, while model fitness was assessed using analysis of variance (ANOVA). From this analysis, optimal phlorotannin and polysaccharide extraction conditions were determined for the evaluated parameters (X1 = 50 °C, X2 = 3.8 W cL−1, X3 = 30 mL g−1 seaweed meal, and X4 = 32.33%). Under these conditions, experimental phlorotannin and polysaccharide yields were 0.73% and 23% (w/w), respectively. Phlorotannin extraction was significantly enhanced by ultrasound power density, while polysaccharide extraction improved when using low ethanol concentration in the solvent, therefore both families of compounds were obtained combining those parameters. Experimental data agreed with predictions from the RSM model, indicating suitability of the obtained model and the success of RSM in optimizing the extraction conditions. In addition, the identification of the main compounds in the phlorotannin extract was carried out by HPLC-MS-TOF; 8 of the 12 identified phenolic compounds belonged to the phlorotannin family, 4 from the fuhalol group, 3 being eckol derivatives, and 1 being a phloroglucinol subunit.