Effects of extracting solvents on phytochemical, antioxidant, and antibacterial activity of some seaweeds from the Bay of Bengal offshore Island

Abstract

Seaweed is a rich source of bioactive compounds. Therefore, searching of natural antioxidant and antibacterial agents as alternatives to a synthetic counterpart is of great interest. The effects of various extracting solvents (viz. methanol, ethanol, and acetone) on the phytochemical content, antioxidant, and antibacterial activity of seven seaweeds consisting of three brown seaweeds (Sargassum natans, Sargassum fluitans, Spatoglossum asperum), three red seaweeds (Hypnea pannosa, Hypnea musciformes, Porphyra linearis) and one green seaweed (Ulva lactuca) were evaluated. The antioxidant capacity of crude extracts was evaluated by total antioxidant activity (TAA), 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2, 2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and cupric reducing antioxidant capacity (CUPRAC) assays. Seaweed extracts were also tested against Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, and Pseudomonas aeruginosa by agar well diffusion method. The total phenolic content (TPC) of seaweed extracts varied significantly (P < 0.05) ranging from 51.08 ± 0.72–74.62 ± 1.15 mg GAE/g. Methanolic extracts of S. natans showed significantly the highest TPC, total flavonoid content (79.22 ± 5.21 mg QE/g), and TAA (57.79 ± 4.35 mg AA/g) than other seaweed extracts. Methanolic extracts of S. natans also exhibited the highest DPPH and ABTS radical scavenging effects (EC50 = 0.74 ± 0.04 and 0.14 ± 0.01 mg/ml, respectively). While, methanolic and ethanolic extracts of S. natans showed significantly the highest effective concentration (ECA0.50) value (0.19 ± 0.02 mg/ml and 0.14 ± 0.02 mg/ml, respectively) of CUPRAC. Pearson's correlation test and principal component analysis showed the relation between TPC and various antioxidant activity assays of seaweed extracts. The seaweed methanolic extracts showed a comparatively higher zone of inhibition against all the bacterial strains than other solvent extracts. However, all the solvent extracts of U. lactuca were almost inactive against all the bacterial strains. The results of this study demonstrated that methanolic extracts of brown seaweeds showed comparatively better antioxidant and antibacterial activity, which could be used in the food and pharmaceutical applications.