Antioxidant activities in vitro of ethanol extract from brown seaweed Sargassum pallidum

The crude extract (CE) was obtained by extracting the powder of Sargassum pallidum with a solution of 70% ethanol. Then, CE dissolved in distilled water was fractionated with chloroform (Cf), ethyl acetate (EtOAc), and n-butanol (n-BuOH), respectively, affording four fractions of Cf, EtOAc, n-BuOH and aqueous. First, the contents of total polyphenols, vitamin C (V-C) and vitamin E (V-E) in CE and its four fractions were determined. As results, the contents of total polyphenols in CE and its fractions decreased in the following order: aqueous fraction > n-BuOH fraction > EtOAc fraction > CE > Cf fraction. The aqueous fraction had significantly higher V-C content (1.82%) compared with CE and fractions of Cf, EtOAc, and n-BuOH (P < 0.05). The contents of V-E in CE and its fractions were all in low level compared with the total polyphenol content and V-C content. Second, the antioxidant activities in vitro of CE and its four fractions were evaluated. Among all the fractions, EtOAc fraction exhibited the highest total antioxidant activity (0.52 mu mol FeSO4 equivalent/mg extract), while fractions of EtOAc and n-BuOH exhibited the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and capacity of chelating iron ions, respectively. In addition, a higher content of total polyphenols (52.08 mg chlorogenic acid equivalent/g extract) and reducing power (0.505 at A(700)) for aqueous fraction were noticed. Finally, it was found that the extracts of S. pallidum contained large amounts of phlorotannin dimers and trimer based on the analytical results of ultra high performance liquid chromatography-mass spectroscopy. The results suggest that S. pallidum can be a good source of natural antioxidant.