Antioxidant and antimicrobial activities of leaves extracts of five Juniperus L. (Cupressaceae) species included in Juniperus section from Turkey

Introduction The genus Juniperus L. (Cupressaceae) comprises about 60 monoecious or dioecious evergreen species, trees or shrubs distributed throughout the Northern hemisphere. The genus is usually divided into three distinct sections or subgenera: Juniperus (syn: Oxycedrus, 9 or 10 species), Caryocedrus (one species, J. drupacea Labill.), and Sabina (approximately 50 species). However, concerning this genus, Flora of Turkey reports only two sections, Juniperus and Sabina Spach., and J. drupacea is included in Juniperus section (Taviano et al., 2011). In Turkish traditional medicine, the species under the Juniperus section are more frequently employed as a folk remedy. Juniperus L. female cones (improperly called “berries”) and leaves have been used by Anatolian people since ancient times as antihelmintic, diuretic, stimulant and antiseptic (Oztürk et al., 2011). In continuation of our studies on Juniperus L. species under Juniperus section from Turkey, this work was designed to evaluate the antioxidant and antimicrobial potential of methanol leaves extracts of J. communis L. var. communis (Jcc), J. communis L. var. saxatilis Pall. (Jcs), J. drupacea Labill. (Jd), J. oxycedrus L. ssp. oxycedrus (Joo), J. oxycedrus L. ssp. macrocarpa (Sibth. & Sm.) Ball. (Jom). Method The total polyphenol content of Juniperus L. spp. leaves extracts was determined spectrophotometrically by the Folin-Ciocalteau reagent. The antioxidant properties were examined by different in vitro methods: DPPH test, reducing power assay, Ferrous ions (Fe2+) chelating activity and TBA assay. Further, the correlation between TPC and antioxidant activity was evaluated. The antimicrobial potential of Juniperus L. spp. extracts against bacteria and yeasts was evaluated by standard methods. The inhibition of biofilm formation was quantified using a microplate-based screening assay (Miceli et al., 2011). Results / Discussion / Conclusion The total polyphenol content (TPC) ranged from 71.77 ± 0.13 mgGAE/g (Jcc) to 133.28 ± 1.74 mgGAE/g (Joo). In the DPPH test the extracts exhibited strong scavenging activity (IC50 from 0.092 ± 0.006 mg/mL Joo to 0.403±0.043 mg/mL Jcc). The extracts showed good reducing power (ASE/mL from 2.56 ± 0.06 Joo to 9.66 ± 0.16 Jd). In the Ferrous ion-chelating assay Jd displayed the strongest effect (IC50 2.65 ± 0.37 mg/mL), whereas Joo and Jom did not manifest any activity. In the TBA assay the extracts showed anti-lipid peroxidation activity (IC50 from 4.39 ± 0.47 μg/mL Jcs to 71.42 ± 3.01 μg/mL Jom). A strong positive correlation between TPC and both DPPH test and reducing power assay was highlighted (R2>0.9); no correlation with Ferrous ion-chelating and TBA assays was found. All the extracts have shown bacteriostatic activity exclusively against S. aureus in the range of 19.53-78.12 µg/mL, and Jd resulted the most effective. The extracts had no significant effect on the S. aureus biofilm formation at sub-minimum inhibitory concentration (MIC) levels. The obtained results give support to the ethnopharmacological use of these Turkish Juniperus L. species, as well as demonstrating the potential of these plants as sources of natural antioxidant and antimicrobial compounds. Bioassay-guided fractionation procedures are necessary to characterize and isolate the active constituents.