Marine algae produce secondary metabolites with antioxidant activity and therapeutic effects. The aim of this study was to evaluate the antioxidant activity of ethyl acetate and methanolic extracts of three algal species: Nannochloropsis oculata (Droop) D.J. Hibberd, Enteromorpha sp., and Polysiphonia scopulorum Harvey. Ethyl acetate and methanolic extracts were prepared using the percolation method and evaluated for DPPH radical scavenging activity, nitric oxide scavenging activity, metal chelating activity, and reducing power activity. The means were compared using the Newman-Keuls Multiple Comparison test. The ethyl acetate extract of N. oculata was found to have the highest total phenol content (82.07 ± 1.32 mg gallic acid equivalent g^-1 of extract). The maximum flavonoid content belonged to Enteromorpha sp. (74.79 ± 0.91 quercetin equivalent g^-1 of extract). The maximum DPPH radical scavenging activity (67.73 ± 0.39%) belonged to ethyl acetate extract of P. scopulorum. The maximum nitric oxide scavenging activity and metal chelating activity belonged to ethyl acetate extract of N. oculata. The highest reducing power activity was observed in the methanolic extract of P. scopulorum. Ethyl acetate extracts of P. scopulorum and N. oculata show significant antioxidant activity, which may be due to their phenolic and flavonoid compounds.

Keywords: marine algae, Nannochloropsis oculata, Enteromorpha sp., Polysiphonia scopulorum, antioxidant activity

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