Antioxidant activities and phenolic contents of three red seaweeds (Division: Rhodophyta) harvested from the Gulf of Mannar of Peninsular India

Abstract

The antioxidant activities of methanol extract and its solvent fractions (n-hexane, dichloromethane and ethyl acetate) of three red seaweeds (Hypnea musciformis, H. valentiae, and Jania rubens) collected from the Gulf of Mannar of South eastern coast of India were evaluated, using different in vitro systems, viz., DPPH, ABTS, HO radical scavenging activities, H2O2 scavenging ability, Fe(2+) ion chelating ability and reducing potential. Folin-Ciocalteu method was used to determine the total phenolic content of the extracts/fractions, and the results were expressed as mg of gallic acid equivalent (GAE)/g of the seaweed extracts/fractions. Thiobarbituric acid-reactive substances (TBARS) inhibition assay was employed to assess the ability of the seaweed extracts/fractions to inhibit lipid oxidation. Ethyl acetate (EtOAc) fractions of H. musciformis exhibited significantly higher total phenolic content (205.5 mg GAE/g), DPPH· scavenging activity (IC50 0.6 mg/mL), ABTS(.+) scavenging activity (IC50 0.51 μg/mL), Fe(2+) chelating ability (IC50 0.70 mg/mL), H2O2 scavenging activity (IC50 0.39 mg/mL), reducing ability (Abs700 nm 1.46) and lipid peroxidation inhibitory ability (2.71 MDAEC/kg) (P < 0.05) compared to its n-hexane, DCM fractions, crude MeOH extract and MeOH extracts/fractions of H. valentiae and J. rubens. DCM fraction of J. rubens showed significantly higher hydroxyl radical scavenging activity (IC50 0.55 mg/mL) compared with H. musciformis and H. valentiae (P < 0.05). This study indicated the potential use of red seaweeds, in particular, H. musciformis as candidate species to be used as food supplement for increasing the shelf-life of food industry, and candidates in combating carcinogenesis and inflammatory diseases.

Keywords: Antioxidant activity; Hypnea sp; Jania rubens; Lipid peroxidation; Phenolics; Red seaweeds.

Fig. 1

Indicative photographs of Hypnea musciformis, H. valentiae and Jania rubens collected from the Gulf of Mannar region in Southeast coast of India (Lat 8º48′ N; Long 78º9′ E and Lat 9º14′ N; Long 79º14′E). The geographical indicators showing the location of the sampling area of the red seaweeds have been illustrated

Fig. 2

IC₅₀ (Inhibition concentration) values for (a) DPPH scavenging activities (mg/mL), (b) ABTS·⁺ scavenging activities (μg/mL), (c) Hydroxyl (HO^.) radical scavenging activities (mg/mL), (d) H₂O₂ scavenging capacity (mg/mL) and (e) Fe²⁺ ion chelating activity (mg/mL). IC₅₀ values were determined from the linear regression curve of scavenging/chelating activities against the different concentrations of seaweed extracts/fractions. IC₅₀ value is defined as the amount of antioxidant necessary to decrease the initial DPPH/ABTS/HO· radicals, H₂O₂ concentration by 50 % and amount of antioxidant necessary to chelate the Fe²⁺ ion by 50 %

Fig. 3

Correlation between antioxidant activity assays by scatter plot analyses. Scatter plot diagrams showing the correlation of total phenolic content (TPC) vis-à-vis (a) DPPH· (n = 12; R² = 0.657), (b) ABTS.⁺ (n = 12, R² = 0.765), (c) H₂O₂ scavenging activity (n = 12, R² = 0.704), (d) reducing ability (n = 12, R² = 0.757), (e) lipid peroxidation (TBARS) inhibitory activity (n = 12, R² = 0.444), (f) Scatter plot showing correlation between DPPH and ABTS radical scavenging activity (n = 12, R² = 0.403)

Fig. 4

Loading plot diagram (various components viz., principal components., PC-1 and PC-2 in rotated space) of antioxidant activities of extracts/fractions from H. musciformis, H. valentiae, and J. rubens. T – Total phenolic content, D - DPPH· scavenging activity, A - ABTS.⁺ scavenging activity, H - HO^. radical scavenging activity, P - H₂O₂ scavenging activity, L - lipid peroxidation inhibitory activity, R – reducing ability, F - Fe²⁺ ion chelating activity. 1, 2, 3 and 4 represents methanol extract, n-hexane, dichloromethane and ethyl acetate fractions, respectively