Validated RP-HPLC Method for Quantification of Phenolic Compounds in Methanol Extracts of Aerial Parts and Roots of Thymus sipyleus and Evaluation of Antioxidant Potential

Purpose: To evaluate the total phenolic content and antioxidant potential of the methanol extracts of aerial parts and roots of Thymus sipyleus Boiss and also to determine some phenolic compounds using a newly developed and validated reversed phase high performance liquid chromatography (RP-HPLC) method. Methods: The total phenolic concentration of the extracts were determined using Folin Ciocalteu method. The antioxidative potential of the samples was evaluated using DPPH and ABTS assays. Phenolics responsible for the antioxidant activity of the plant were quantified by a newly developed and validated RP-HPLC method for the first time. Results: The total phenolic concentration of the aerial parts and roots were 215.1 ± 2.24 and 152.25 ± 2.31 mg GAE/g extracts, respectively. The extract obtained from the aerial parts reduced DPPH with a half-maximal inhibition concentration (IC50) of 0.703 ± 0.027 mg/mL, while the IC50 obtained from ABTS assay was 0.869 ± 0.066 mg/mL. IC50 values of Trolox used as standard for DPPH and ABTS radical scavenging assays were 0.0430 ± 0.0001 and 0.0420 ± 0.0001 mg/mL, respectively. The results revealed that T. sipyleus contains remarkable amounts of rosmarinic acid in the aerial parts (0.8887 ± 0.0016 g/100g dw) and in the roots (0.3454 ± 0.0006 g/100g dw) which is believed to be mostly responsible for the observed activity. Conclusion: T. sipyleus is a major potential antioxidant source for the food, pharmaceutical and cosmetic industry due to its high contents of rosmarinic acid and total phenolics.