Optimized extraction of polyphenols with antioxidant and anti-biofilm activities and LC-MS/MS-based characterization of phlorotannins from Sargassum muticum

The Sargassum genus is rich in glycoglycerolipids, phytosterols, terpenoids, polyphenols, nitrogenous compounds, and other components, and it exhibits various biological activities. Response surface methodology optimization based on Box-Behnken design was applied to extract polyphenols with antioxidant and anti-biofilm activities from Sargassum muticum. Results indicated that the optimal extraction conditions were an ethanol concentration of 56%, a temperature of 58 °C, a time of 5 h, and a liquid/material ratio of 40 mL/g. Under these conditions, the contents of polyphenols and phlorotannins were 10.76 ± 0.42 mg/g and 1.62 ± 0.04 mg/g, respectively. The EtOH extract of S. muticum was further purified with organic solvents of different polarities, and the ethyl acetate fraction (HA-PTs) exhibited the highest purity of polyphenols and phlorotannins, along with the best antioxidant and anti-biofilm activities. In phytochemical analysis, the main substances identified were polysaccharides, phytosterols, polyphenols, flavonoids, and phlorotannins. According to UHPLC-DAD-ESI-MS/MS analysis, four types of phlorotannins were identified from HA-PTs: dibenzodioxine-1,3,6,8-tetraol, tetraphlorethol, pentaphlorethol, and fucopentaphlorethol. These results indicate that the polyphenols of S. muticum have the potential to become new natural antioxidants and antibacterial agents.