Essential oil composition, total phenolic, flavonoid contents, and antioxidant activity of Thymus species collected from different regions of Iran

Abstract

In this study, the essential oil (EO) composition, flavonoid and phenolic contents, and antioxidant activities of fourteen Thymus accessions belonging to ten species were evaluated. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the presence of 38 compounds with the major constituents including thymol (12.4-79.74%), carvacrol (4.37-42.14%), geraniol (0.3-22.44%), and p-cymene (0.8-12.86%). Cluster analysis identified three groups of high thymol, geraniol/linalool, and high carvacrol. The highest phenolic and flavonoid contents were detected in T. daenensis-1 (70.6mg tannic acid equivalents (TAE) g^-1 DW) and T. vulgaris (8.55mg quercetin equivalents (QE) g^-1 DW), respectively. The antioxidant activities of the samples were determined using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and reducing power assay. The results demonstrated that T. daenensis-3 (IC₅₀=273.36), T. vulgaris (IC₅₀=289.3), and T. fedtschenkoi-3 (IC₅₀=339.22) possessed higher antioxidant activities than the others. Finally, the Thymus species with high bioactive compounds may be recommended for further food applications.

Keywords: Antioxidant activity; DPPH; Essential oil; Reducing power; Thyme.