Physicochemical and biofunctional properties of Sargassum thunbergii extracts obtained from subcritical water extraction and conventional solvent extraction

The aim of this study was to analyze Sargassum thunbergii extracts prepared via subcritical water extraction (SWE). The total maximum contents of phlorotannin, total sugars, and reducing sugars of the S. thunbergii extracts were (13.57 ± 0.19) mg phloroglucinol equivalent (PGE)/g of dry sample, (61.95 ± 0.75) mg glucose/g of dry sample, and (48.51 ± 1.40) mg glucose/g of dry sample in extracts prepared at 180 °C, 150 °C, and 180 °C, respectively. The antioxidant activity of S. thunbergii extracts in the ABTS, DPPH, and FRAP assays was the highest at extraction temperature of 180 °C, with values of (17.99 ± 0.02, 56.72 ± 0.09, and 29.79 ± 0.11) mg Trolox equivalent (TE)/g of dry sample, respectively. In the extract prepared at 180 °C, the largest range of phenolic compounds was identified, and the antibacterial activity was strongest. In the agar well diffusion assay, 50 mg/mL S. thunbergii extract obtained at 180 °C resulted in the largest zones of clearance for Escherichia coli and Bacillus cereus and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were higher for E. coli than for B. cereus.