Antioxidant potential of solvent extracts of Kappaphycus alvarezii (Doty) Doty – An edible seaweed

Various solvent extracts of Kappaphycus alvarezii, an edible red seaweed (family Solieriaceae) were screened for total phenol content and antioxidant activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferrous ion chelating activity, reducing power and antioxidant activity assays in a linoleic acid system with ferrothiocyanate reagent (FTC). The total phenol content of different extracts of K. alvarezii varied from 0.683 ± 0.040% to 2.05 ± 0.038%. The radical-scavenging activity of ethanol extract was, as IC₅₀ 3.03 mg ml⁻¹, whereas that of the water extract was IC₅₀ 4.76 mg ml⁻¹. Good chelating activity was recorded for methanol extract (IC₅₀ 3.08 mg ml⁻¹) wherein 67.0 ± 0.924% chelation was obtained using 5.0 mg ml⁻¹ of extract. The reducing power of the samples was in the following order: BHT > methanol > ethanol > ethyl acetate > water > hexane. But, in the linoleic acid system, the ethanol extract proved superior to the synthetic antioxidants butylated hydroxytoluene (BHT). Hence, these extracts could be considered as natural antioxidants and may be useful for curing diseases arising from oxidative deterioration.