Indian Journal of Geo-Marine Sciences Vol. 43 (4), April 2014, pp. 507-518 Antioxidant activity and phytochemical analysis of a few Indian seaweed species Dharmesh R Chejara a,b , Stalin Kondaveeti a , Ramavatar Meena a,b & A. K. Siddhanta a,b * a Marine Biotechnology & Ecology Discipline, CSIR-Central Salt & Marine Chemical Research Institute G.B.Marg, Bhavnagar-364002, Gujarat, India b Academy of Scientific & Innovative Research, Anusandhan Bhavan, 2 Rafi Marg, New Delhi-110001, India [E-mail: aks@csmcri.org] Received 19 August 2013; revised 25 February 2014 Antioxidant activities of crude methanol extracts and fractions of the seaweed species viz. Bryopsis plumosa (BP), Dictyopteris australis (DA) and Gracilaria pudumadamensis (GP) of Indian waters were evaluated and correlated with their phytochemical contents. In DPPH assays the most promising antioxidant sample was the crude methanol extract (BP M ), which was comparable with standard antioxidant BHT. In the superoxide radical activity assays no sample in the group was as active as BHT, however the promising ones were DA M , DA E and GP M , GP E , GP H (subscripts M, E and H stand for the respective methanol extracts and their ethyl acetate and hexane fractions). In the Fe 2+ chelating activity assays EDTA showed far stronger activity than those of the promising samples. In reducing power assays BP M , BP E , and BP H showed comparable activity with BHT at a concentration 0.5 mg/mL. Thus these seaweed species would be of potential utility as a source of natural antioxidants. [Keywords: Seaweeds, Antioxidant activity, Phytochemicals, Bryopsis plumosa, Dictyopteris australis, Gracilaria pudumadamensis] Introduction against these damaging ROS species, antioxidants play an important role inhibiting the oxidation of lipid and other biomolecules by blocking the initiation step as well as scavenge various free radicals thereby detoxifying the organism 6 . Commonly used and commercially available antioxidants such as BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) have been reported to be responsible for liver damage and carcinogenesis 7-8 . Therefore, search for natural antioxidants was initiated resulting in the identification of various antioxidants in higher plants 9-10 . Seaweeds have been reported to be a rich source of antioxidant compounds 11-12 . The antioxidant properties of some specific brown and red seaweeds from across the globe were reported 13-19 . Phenolic * Correspondence Over the past several decades seaweeds and their extracts have been studied as novel sources of variety of compounds and some of them were reported to possess biological activity for potential medicinal value 1-2 . Oxidative and free radical damages of cell metabolism play an important role in the living systems attracting increased attention of researchers. 3 Formation of Reactive Oxygen Species (ROS) is a common process during cellular metabolism and there are various forms of activated oxygen species commonly known as hydroxyl radicals and superoxide anion radicals etc., which harm the living cells. 4 The possibilities of some anti oxidative defence mechanisms in plants including seaweed cells were proposed by Matsukawa et al., (1997) 5 . To combat