Extraction, purification, chemical characterization and antioxidant properties in vitro of polyphenols from the brown macroalga Ascophyllum nodosum

This study aims to investigate enzyme-assisted extraction (EAE) and ultrasound-assisted enzyme extraction (UAEE) using several enzymes (viscozyme or alcalase) and extraction time (1–4 h) for the extraction of polyphenols from brown macroalga Ascophyllum nodosum. The extraction yields and antioxidant activities of polyphenols were evaluated. The extracts using the most efficient extraction method were further purified by liquid-liquid partition and identified by UHPLC-hybrid quadrupole-orbitrap mass spectrometry. Polyphenols were separated by molecular weight cut-off filtration (MWCO) or gel filtration (Sephadex LH-20). UAEE (alcalase, 3 h) achieved the highest extraction yields (1913.33 mg phloroglucinol equivalents (PGE)/100 g dry weight (DW) macroalgae). Ethyl acetate fractions purified using liquid-liquid partition achieved the highest polyphenols content (73.85 g PGE/100 g extract), and 74 % of this fraction had molecular weight >10 kDa. Less polar polyphenols, separated from the ethyl acetate fraction by gel filtration had the highest antioxidant activities. Twelve polyphenols were identified in the ethyl acetate extract. This research provides a strong support for expanding the application of polyphenols derived from A. nodosum by identifying both a suitable extraction process as well as identifying the polyphenols with antioxidant activities for their future use as nutraceuticals or pharmaceuticals.