Antioxidant activity and phenolic profile in filamentous cyanobacteria: the impact of nitrogen

In the present study, ethanolic extracts of ten cyanobacterial strains cultivated under different nitrogen conditions were assessed for the phenolic content and antioxidant activity. The amount of detected phenolic compounds ranged from 14.86 to 701.69 mu g g(-1) dry weight (dw) and HPLC-MS/MS analysis revealed gallic acid, chlorogenic acid, quinic acid, catechin, epicatechin, kaempferol, rutin and apiin. Only catechin, among the detected phenolics, was present in all the tested strains, while quinic acid was the most dominant compound in all the tested Nostoc strains. The results also indicated the possibility of increasing the phenolic content in cyanobacterial biomass by manipulating nitrogen conditions, such as in the case of quinic acid in Nostoc 2S7B from 70.83 to 594.43 mu g g(-1) dw. The highest radical scavenging activity in DPPH assay expressed Nostoc LC1B with IC50 value of 0.04 +/- 0.01 mg mL(-1), while Nostoc 2S3B with IC50 = 9.47 +/- 3.61 mg mL(-1) was the least potent. Furthermore, the reducing power determined by FRAP assay ranged from 8.36 +/- 0.08 to 21.01 +/- 1.66 mg AAE g(-1), and it was significantly different among the tested genera. The Arthrospira strains exhibited the highest activity, which in the case of Arthrospira S1 was approximately twofold higher in comparison to those in nitrogen-fixing strains. In addition to this, statistical analysis has indicated that detected phenolics were not major contributor to antioxidant capacities of tested cyanobacteria. However, this study highlights cyanobacteria of the genera Nostoc, Anabaena, and Arthrospira as producers of antioxidants and phenolics with pharmacological and health-beneficial effects, i.e., quinic acid and catechin in particular.