Cell-free extracts of twenty terrestrial cyanobacteria were evaluated for their antioxidant properties in terms of free-radical scavenging (DPPH and ABTS) and metal chelating activity and deoxyribose protection. Extract of Anabaena constricta was the most prominent antioxidant agent (IC 50 for DPPH activity 0.91 mg ml -1 , ABTS 0.23 mg ml -1 , deoxyribose protection 0.63 mg ml -1 and Fe ?2 -ion chelating 0.9 mg ml -1 ). The extracts of cyanobacterial species contained high quantity of total phenol and total flavonoid that were supposed to impart prominent antioxidant properties. Cyanobacterial species also showed fairly high PAL activity. We reported varied quantities of polyphenolics gallic, chlorogenic, caffeic, vanillic and ferulic acids and flavonoids rutin, quercetin and kaempferol in cyanobacterial extracts. The presence of these polyphenolics was linked with the free radical scavenging, metal chelating and antioxidative damage protecting properties of the organisms. Cyanobacteria are the most feasible, promising and alternative candidates for searching out new chemical leads for industrial applications in pharmaceuticals, neutraceuticals and biomolecules of importance. Presence of biomolecules such as polyphenolics and their connection with the prominent biological functions (e.g., antioxidant properties) make these organisms a potential source of secondary metabolites with predominant biological activities. Additionally, dominant presence of polyphenols as antioxidant agents in cyanobacterial species may reflect their adaptation strategies against abiotic stresses for their ecological success in different habitats.

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