A Comparative Study on the in vitro Antioxidant and Antimicrobial Potentials of Three Endemic Ononis L. Species from Turkey

Objectives: In this study, the antioxidant capacity, antimicrobial activity and phenolic contents of aerial parts and roots extracts of three endemic Ononis L. (Leguminosae) species (O. sessilifolia Bornm., O. basiadnata Hub. & Mor., O. macrosperma Hub. & Mor.) were investigated for the first time.

Materials and methods: The phenolic contents of the extracts [water and ethanol (EtOH)] and fractions [dichloromethane, EtOAc and n-butanol] were determined using Folin-Ciocalteu's phenol reagent. Also, their antioxidant capacities were studied using qualitative DPPH˙ (1,1-diphenyl-2-picrylhdrazyl radical) and TBA assays. The antimicrobial activity of these extracts and fractions compared with standard antibiotics were studied using disc diffusion assays against various Gram-positive and Gram-negative bacteria and fungi.

Results: The total phenolic contents of the water extracts were found to range between 14.78-80.33 mg/g, and the EtOH extracts ranged from 67.19-145.33 mg/g. EtOAc fractions of the three species were rich in terms of total phenolic contents when compared with other extracts (242.56-620.89 mg/g). The most significant results in the TBA assays were obtained in EtOH extracts of O. macrosperma (IC₅₀=0.13±0.17 µg/mL), O. sessilifolia (IC₅₀=1.41±0.58 µg/mL) and root (IC₅₀=1.96±0.39 µg/mL).

Conclusion: EtOAc fractions rich in phenolic content were also found to be the most effective in antioxidant activity assays. Although all water extracts had no antimicrobial activity, EtOH extracts and n-butanol fractions showed generally moderate activity against bacteria. Some EtOAc fractions except for O. sessilifolia showed less activity against Escherichia coli, Staphylococcus aureus, MRSA and Candida albicans.

Keywords: Ononis basiadnata; Ononis macrosperma; Ononis sessilifolia; antimicrobial activity; antioxidant capacity; endemic.