Phenolic composition and antioxidant activity of thedifferent extracts from Thymus longicaulis C Presl. subsp longicaulis var. longicaulis and T. longicaulis C. Presl. subsp longicaulis var. subisophyllus growing in Turkey

Abstract

The objectives of the present study were to investigate the phenolic composition and in vitro antioxidant capacities of the infusions and different extracts of two Thymus taxa: Thymus longicaulis C. Presl. subsp. longicaulis var. longicaulis and Thymus longicaulis C. Presl. subsp. longicaulis var. subisophyllus (Lamiaceae). The quantitative estimation of total flavonoid, flavonoland phenolic contents of the studied extracts were performed by spectrophotometrical method; the aluminum chloride the aluminum chloride+Na acetate and Folin-Ciocalteau methods, respectively. The determination of phenolic acids in the studied species was achieved by using a modified reverse phase-High Pressure Liquid Chromatography method adopting an internal standard. Antioxidant activities of the extracts were determined by three test systems namely, radical scavenging on DPPH, beta-carotene bleaching and Rancimat methods. The results were compared to those of BHT as synthetic antioxidant. Ethyl acetate extracts were found to be rich as a source of phenolics. In addition, the main phenolic acid of the extracts identified by HPLC-DAD was rosmarinic acid. Also, the infusions containing especially water-soluble compounds were observed to exhibit lower antioxidant capacities than those of the methanol and ethyl acetate extracts. Our results indicated that ethyl acetate fraction of studied Thymus taxa can be used as antioxidant in food and medicinal preparations. In addition, the present study revealed that the infusions of these plants exhibit lower activity in contrast to general believes in which aqueous extracts, as in the case of herbal teas, have high antioxidant activity.