Phenolic Profile and In vitro Antioxidant Activity of Endemic Bulgarian Carduus Species

Background: Plant species from genus Carduus are widely distributed in the world and represented in Bulgaria by 14 species. Previous investigations on this genus demonstrated a strong antioxidant potential of extract from some Bulgarian Carduus species. Objective: The present study investigates the phenolic profile and the antioxidant potential of different extracts obtained from four endemic Compositae herbs, growing wild in Bulgaria: Carduus armatus Boiss and Heldr., Carduus candicans Waldst. et Kit ssp. globifer (Velen.) Kazmi., Carduus rhodopaeus Velen. and Carduus thracicus (Velen.) Hayek. Materials and Methods: Antioxidant capacity of the obtained extracts was estimated with 2,2-diphenyl-1-picrylhydrazyl, 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid), and ferric reducing antioxidant power and copper reduction antioxidant assays. Phenolic profile was estimated by high performance liquid chromatography. Results: Eleven phenolic acids and eight flavonoids were quantified in the inflorescences. Sinapic (2760.72 ± 15.68 µg/g dry weight [dw]), chlorogenic (2564.50 ± 19.73 µg/g dw) and ferulic acids (1648.71 ± 19.57 µg/g dw), as well as luteolin (2345.45 ± 18.61 µg/g dw) and apigenin (1332.75 ± 12.05 µg/g dw) were found to be the predominant compounds. The above contents are the highest values found in C. candicans ssp. globifer. The highest established antioxidant activity (AOA) was in favor of the ethanolic extracts, and the extract of C. rhodopaeus affirmed with the highest AOA among the investigated plant species. Conclusion: All identified phenolic compounds were reported for the 1st time in the studied endemic Carduus species, as well as their antioxidant capacities. The present study revealed that these plant species could be used as sources of antioxidants with potential medicinal properties.