Phenolic Compounds, Antioxidant Capacity, and DNA-Protective Properties of Onopordum carduchorum Flower Extracts

This study presents the first comprehensive report on the phenolic composition, antioxidant activities, antimicrobial properties, and DNA protection potential of methanol and water extracts from flower parts of Onopordum carduchorum collected in the Gaziantep region of Turkey. In quantitative chromatographic analysis, bioactive compounds such as chlorogenic acid, 4-hydroxybenzoic acid, syringic acid, pinoresinol, protocatechuic acid, caffeic acid, and apigenin were detected in both extracts, with a total of 22 phenolic compounds found. While the total phenolic content was higher in the aqueous extract (35.41 mg GAE/g), the methanol extract showed a higher flavonoid content (13.80 mg RE/g) (p < 0.05). The aqueous extract exhibited significant antioxidant activity in DPPH, ABTS, FRAP, CUPRAC, metal chelation, and phosphomolybdenum tests, showing lower IC₅₀ and EC₅₀ values compared to the methanol extract (p < 0.05). In contrast, the methanol extract showed relatively weaker antioxidant potential with higher IC₅₀ and EC₅₀ values in all analyses. Both extracts showed protective effects on DNA and provided significant protection against UV radiation. In contrast, no antimicrobial activity was observed against the tested strains. This study presents the first report on O. carduchorum flowers and provides baseline data to explore their phenolic profiles, antioxidant, and UV-protective potential.