Evaluation of the Antioxidant Capacity and Phenolic Content of Three Thymus Species

Thymus species are known to have significant amounts of phenolic and flavonoid compounds and exhibit strong antioxidant activities. This work was designed to evaluate the antioxidant activities of three endemic Iranian Thymus species (including T. daenensis, T. kotschyanus, and T. pubescens) in different test systems [namely DPPH (2,2′-diphenyl-1-picrylhydrazyl), ABTS+ [2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid], and linoleic acid/β-carotene bleaching assays] to determine the total phenolic and flavonoid contents of the species (assayed by colorimetric techniques) and to study the possible composition-activity relationship. All the tested plants exhibited concentration-dependent antioxidant and free radical scavenging activities. T. pubescens showed the highest free radical scavenging activities in both DPPH and ABTS+ methods, while T. daenensis and T. kotschyanus were the most active species in the β-carotene bleaching inhibition test. Alternatively, T. pubescens exhibited a significantly higher level of the total flavonoid content compared with those of the other species, while no significant statistically differences were found among the tested plants regarding the total phenolic content. In addition, significant correlations were found between the flavonoid content and DPPH/ABTS+ radical scavenging activities, but not between the β-carotene bleaching inhibition system and the flavonoid content.