In vitro antioxidant activity
was determined by DPPH radical scavenging assay, ferric-reducing antioxidant power (FRAP) assay,
ferrous ion chelating (FIC) assay, โ-carotene bleaching (BCB) assay and total phenolic content (TPC)
quantification. Cytotoxicity was evaluated with the brine shrimp Artemia sp. lethality test. The TPC values
observed in the present study indicated that both species A. multifida and M. echinocarpa are rich in
phenolic compounds, reaching values of 45.40 and 28.46 mg gallic acid equivalent (GAE) g-1 of ethanolic
extract, respectively. DPPH radical scavenging and ferrous ion chelating showed values of 60% and 17%,
respectively. Both seaweed extracts inhibited โ-carotene oxidation by approximately 40%. None of the
algal extracts were potentially cytotoxic. The results have showed that extracts of both species of marine
red algae exhibit antioxidant potential and low toxicity. They are sources of natural antioxidant compounds.