Effect of physicochemical parameters of seawater on antioxidant capacity in green, brown, and red macroalgae from the Persian Gulf

The present study aimed to investigate the effect of seasonal variations in physicochemical parameters of seawater including temperature, pH, dissolved oxygen, electrical conductivity, total suspended solids, total nitrogen, and total phosphate, on the antioxidant capacity of the green, brown, and red algae from the northern coasts of the Persian Gulf. The algal collection involved 34 samples (18, 9, and 7 green, brown, and red macroalgae, respectively) from 4 different months of the year 2016 (March, May, October, and December). Antioxidant activity was evaluated by the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging assay. Total phenolic and flavonoid contents were determined using the Folin-Ciocalteu’s reagent and the colorimetric method, respectively. Water sampling was performed at two-day intervals on days 6, 4, and 2 before algal sampling. Results revealed that the highest phenolic content and antioxidant capacity were observed in October for the sampled brown algae, whereas for red algae the highest antioxidant capacity was obtained in December. Higher levels of flavonoids were noticed in the green algae in October. In both green and red algae, there was a negative significant correlation between IC50 and flavonoids, whereas in the brown algae a negative significant correlation was observed between IC50 and phenolic content. In a multivariate regression model, the main and interaction effects of each variable were examined. The antioxidant parameters were influenced by temperature, dissolved oxygen, and total nitrogen. pH at different levels of algal groups showed different effects on IC50, phenolic, and flavonoid contents.