Saponins and the in vitro bioactivities of different solvent extracts of some tropical green and red seaweeds

Objective: To evaluate the antioxidant and antimicrobial activities of the saponins content and the corresponding sequential extracts prepared using petroleum ether, chloroform, ethyl acetate and acetone, of some seaweed species [consisting of red Gracilaria corticata, Gracilaria corticata var. cylindrica and Gracilaria foliifera and green Enteromorpha prolifera, Ulva fasciata and Chaetomorpha antennina (C. antennina) seaweeds], obtained from the southwest coast of India. Methods: The fractions were collected during the extraction of saponins and the saponins were chemically investigated for the saponification and iodine value. The antioxidant activities were estimated using the 2,2-diphenyl-1-picrylhydrazyl, UV-vis ferrous tartrate and KMnO4 titration methods against four standards. The antimicrobial activities were estimated against four pathogenic organisms. Bioactive fractions except saponins, were further investigated through gas chromatography-mass spectrometer. Statistical correlations were done to identify the correlation pattern between the activity and constituents. Results: The seaweed extracts exhibited appreciable biochemical activities. In general, the Chlorophyta had rich resource of saponins. C. antennina showed high content of saponins. Antioxidant activities were seen to be high when the saponins and fatty acid fractions were screened. C. antennina, Enteromorpha prolifera, Gracilaria corticata var. cylindrica and Gracilaria foliifera exhibited commendable antioxidant activities. Antibacterial activity was exhibited the highest in the extracts of Ulva fasciata. Selective antimicrobial inhibition was observed throughout. Gas chromatography-mass spectrometer investigation showed appreciable contents of ω-3, ω-5, ω-6, ω-7, ω-8, ω-9 and rare ω-11 fatty acids along with other saturated fatty acids. Conclusions: The correlation studies underlined the relation between the biochemical compositions and activities. These seaweeds could be considered as a potential source of valuable natural antioxidants, antibiotics and nutraceutical compounds