Comparative analysis of specialized metabolites and antioxidant capacity in vitro of different natural populations of Globularia spp.

Total phenolic, flavonoid, condensed tannin and iridoid content, as well as antioxidant capacity in vitro, were determined spectrophotometrically in methanolic extracts of different plant parts of the Mediterranean medicinal plant Globularia alypum L. and three widespread European species of the same genus: G. cordifolia L., G. meridionalis (Podp.) O. Schwarz and G. punctata Lapeyr. In order to consider possible environmental influences on the production of specialized metabolites, each species, except G. alypum, was collected from three different natural populations. Great variations in the amounts of specialized metabolites were observed among different plant parts and species. For example, total phenolic content ranged from 10.13 (G. punctata, flowers) to 44.90 (G. cordifolia, flower stems) mg gallic acid equivalent g–1 dry weight. Moreover, great differences, attributed to location-specific environmental factors, were observed among different populations of the same species. For example, a strong positive correlation was observed among mean monthly temperatures and total phenolic contents in the leaves of studied Globularia spp. (r = 0.75, p = 0.019). However, despite these differences, all species were rich in bioactive substances when compared to G. alypum, especially in their aerial parts. A very good positive correlation was observed between total phenolic content and DPPH radical scavenging capacity (r = 0.86, p <0.001)/ABTS radical scavenging capacity (r = 0.83, p < 0.001). The results obtained show that G. cordifolia, G. meridionalis and G. punctata are rich in bioactive substances, providing support for their pharmaceutical utilization. Further investigations are needed to verify the possibility of their medicinal use