The antioxidative properties of phlorotannins isolated from the brown alga Eisenia bicyclis were measured using the H-ORAC (Hydrophilic Oxygen Radical Absorbance Capacity) method. The ORAC values of phloroglucinol and it's oligomers: eckol, fucofuroeckol A, phlorofucofuroeckol A, dieckol, 8,8'-bieckol, were 2.57 ± 0.14, 4.97 ± 0.36, 9.82 ± 0.70, 8.97 ± 0.89, 10.22 ± 0.85, 8.62 ± 0.92 μmol Trolox equivalent/μmol, respectively. With the exception of eckol, the ORAC values of tested phlorotannins

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... ere higher than those of the well-known antioxidants (epigallocatechin gallate, resveratrol and L-ascorbic acid) used as positive controls. As a result of comparing with known ORAC values, it was found that the dieckol and fucofuroeckol A had stronger antioxidant activity than representative polyphenols (e.g., kaempferol, quercetin, myricetin and chlorogenic acid) derived from terrestrial plants.