In this study, we aimed to elucidate the antioxidant capacity of Eisenia bicyclis and evaluated its antioxidant activity using various assay systems such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, 2,2-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging, reducing power ability, and content of total polyphenol. Among all the performed experiments, the ethyl acetate fraction of E. bicyclis exhibited higher antioxidant activities. From this finding, isolation and purification were performed on the ethyl acetate fraction and identified dieckol and phlorofucofureoeckol-A by spectroscopic analyses including FAB-mass in the negative mode, 1H NMR, 13C NMR, 1H-1H COSY, HMQC, and HMBC spectra. Interestingly, ABTS radical scavenging activities of dieckol and phlorofucofuroeckol showed strong effects of 65.36% and 70.38% at a concentration of 50 μg/mL, respectively. DPPH radical scavenging and reducing power abilities were increased in a dose-dependent manner at various concentrations. These results suggest that dieckol and phlorofucofuroeckol-A of E. bicyclis may play an important role in protection from oxidative stress involving reactive oxygen species and may contribute to the development of new bio products, for example, a useful preservative to improve food quality and a drug for various oxidative damage-associated diseases.
Practical Application: The results suggest that dieckol and phlorofucofuroeckol-A can be utilized as a natural source for potential application of antioxidant in food industry and drug for oxidative damage-associated diseases.