Seaweeds are now recognized as a treasure of bioactive compounds. However, the bioactivity of seaweed originating in Bangladesh is still unexplored. So, this study was designed to explore the secondary metabolites and antioxidant activities of solvent extracts of Padina tetrastromatica and Gracilaria tenuistipitata. Phytochemical screening and FTIR spectra confirm the diverse type of bioactive compounds. Antioxidant activity of extracts were evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2, 2-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), reducing power (RP), phosphomolybdenum, hydrogen peroxide and nitric oxide (NO) scavenging assays. Here, methanolic extract of P. tetrastromatica showed highest amount of total phenolic content (85.61 mg of GA/g), total flavonoid content (41.77 mg of quercetin/g), DPPH (77.07%), ABTS (77.65%), RP (53.24 mg AAE/g), phosphomolybdenum (31.58 mg AAE/g), hydrogen peroxide (67.89%) and NO (70.64%) assays compared to its methanolic extracts of G. tenuistipitata. This study concluded that methanol as a solvent extract of brown seaweed (P. tetrastromatica) exhibited bioactivity and antioxidant potentiality which will be useful for pharmacological as well as in functional food application.

Seaweeds are now recognized as a treasure of bioactive compounds. However, the seaweed of Bangladesh is still unexplored. So, this study was designed to explore the secondary metabolites and antioxidant activities of solvent extracts of Padina tetrastromatica and Gracilaria tenuistipitata. Phytochemical screening and Fourier transform infrared (FTIR) confirm the diverse type of bioactive compounds. Antioxidant activity of extracts were evaluated by 1, 1-diphenyl-2- picrylhydrazyl (DPPH), 2, 2-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), reducing power (RP), phosphomolybdenum and hydrogen peroxide assays. Here, methanolic extract of P. tetrastromatica showed the highest amount of total phenolic content (85.61 mg of GA/g), total flavonoid content (41.77 mg of quercetin/g), which showed as potent antioxidant properties confirmed by DPPH (77.07%), ABTS (77.65%), RP (53.24 mg AAE/g), phosphomolybdenum (31.58 mg AAE/g) and hydrogen peroxide (67.89%) assays followed by ethanol and water. This study concluded that bioactive compound and antioxidant activities are dose and solvent-dependent and seaweed type.