Temporal, Plant Part, and Interpopulation Variability of Secondary Metabolites and Antioxidant Activity of Inula helenium L.

Variations in abiotic environmental factors have significant effects on quantity and quality of secondary metabolites, which is particularly important for plant species that possess biologically active compounds. The purpose of this study is determination of the total phenolic content, flavonoid concentration, and antioxidant activity of the different parts of Inula helenium L. (Asteraceae) sampled from different populations and in different time periods. The amounts obtained for the total phenolics varied from 16.73 to 89.85 mg of gallic acid (GA)/g. The concentration of flavonoids ranged from 9.32 to 376.22 mg of rutin (Ru)/g. The IC₅₀ values of antioxidant activity determined using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical method varied from 161.60 to 1563.02 μg/ml. The inflorescence and roots possessed high concentration of phenolic compounds and significant antioxidant activity, while leaves contained the highest concentration of flavonoids. Additionally, the quantity of the phenolics, as well as antioxidant activity, significantly varied among the different populations due to different impacts of environmental factors. This research showed that I. helenium represents an abundant source of bioactive substances, and that the quantity of these compounds greatly differs among the different populations as well as in the same populations regarding the different time periods as well as plant parts.