Polyphenols extraction kinetics from Ascophyllum nodosum seaweed employing water and saltwater: Effect of ultrasound sonication

Saltwater (S), with the same ionic strength of seawater, was employed as solvent to extract polyphenols from seaweeds. Aqueous extracts were chemically characterized by means of total polyphenols (TPC), carbohydrates (CHOS) and uronic acids (UA) content and antioxidant capacities (DPPH, ABTS and FRAP). S-extracts showed lower TPC than those obtained with distilled water (D) using two different extraction methods, conventional solid-liquid extraction (SLE) and ultrasound-assisted extraction (UAE). The antioxidant capacities of both non-sonicated extracts did not show significant (p < 0.05) differences. SLE kinetics employing both solvents (D and S) were successfully modelled by Peleg's model, and equilibria were achieved after 15 min. Long-time UAE (15 min) increased phytochemical content in both D- and S-extracts with respect to SLE. Extracts showed three main (A, B, and C) regions from RP-HPLC profiles with different peak areas and shapes. Normalized regions areas from RP-HPLC were related to antioxidant activities by linear regressions and showed that B-region was the main responsible of phytochemical features of the extracts. SLE with saltwater promoted the leaching of other compounds (mainly proteins) that formed intermolecular complexes. These interactions were notoriously diminished with UAE. At these conditions, saltwater can be employed as eco-friendly solvent according to the green chemistry principles.