Abstract

The antioxidant activities of Methanol/Chloroform (MC) extracts and fractions of five brown algae (Sargassum fusiforme, Sargassum kjellmanianum, Sargassum. pallidum, Sargassum thunbergii and Sargassum horneri) from China were evaluated through DPPH/hydroxyl radical-scavenging activity and reducing power. Total phenolic content was investigated using Folin–Ciocalteau reagent. The MC extract of S. kjellmanianum showed higher antioxidant activity than other seaweeds. However, the MC extracts of all the seaweeds showed lower DPPH radical-scavenging activity than Gallic Acid (GA) and ascorbic acid (AscA) at 50 µg/ml. The MC extracts were further purified by liquid–liquid partition to afford four fractions: Petroleum Ether (PE), Ethyl Acetate (EA), Butanol (BU) and Aqueous (AQ), among which the EA was found to be the most effective fraction and showed higher antioxidant activity than AscA, except that the EA fraction of S. thunbergii presented lower reducing power than GA. Antioxidant activities of MC extracts showed an increase with increasing concentration (between 15 and 45 μg/ml) indicating the dose dependency of these properties. The phenolic compounds with highest activities were concentrated in the EA fraction and were of medium polarity. The finding showed that the antioxidant-rich extracts or fractions had a significant potential to be use as a natural antioxidant agent.

Key words: Brown seaweeds, Sargassum, antioxidant activity, phenols content.