# Chemical Composition and Antioxidant Activities of Three Bulgarian Garden Thyme Essential Oils
## 1 Introduction  
Thyme is a herbaceous, perennial plant of the _Lamiacane_ family, known since ancient times for its medicinal properties. About 350 species have been identified in the genus _Thymus_, which differ in habit, growth, development, amount, and composition of biologically active substances--essential oil, polyphenolic acids, flavonoids, etc. Garden thyme (_T. vulgaris_ L.) and common thyme (_T. seryllium_ L.) are industrially important for obtaining essential oils and extracts. Different chemotypes are known from these two species, which contain in their essential oil various aromatic substances, for example, the phenols thymd and carvacrol, the hydrocarbons p-cymene and \(\gamma\)-terpinene, as well as many other components in different proportions [1,2]. Garden thyme (_T. vulgaris_) originates from the Mediterranean part of Europe and Africa. It is grown in countries located in Southern and Northern Europe, North Africa, and North America [1,2]. The main component is its essential oil, which in dry plant material ranges in quantities of 0.32-4.90% [1, 2, 3, 4, 5, 6, 7, 8, 9]. Wild or cultivated plants, depending on the region of growth, have a different chemical composition, which is determined mainly by soil and climatic factors [2; 10; 11; 12; 13]. [PERSON] et al. [10] examined the composition of four essential oils of the species _T. vulgaris_ for different chemotypes, and found the following: linalool chemotype (linalool, 76.2%; linaly acetate, 14.3%); geraniol chemotype (geraniol, 59.8%; geranyl acetate, 16.7%); sabinene hydrate chemotype (cis-sabinene hydrate, 30.8%; trans-sabinene hydrate, 5.0%); and thymol chemotype (thymol, 47.1%; p-cymene, 20.1%). [PERSON] et al. [11] determined the chemical composition, and antimicrobial and antioxidant activity of five essential oils of the species _T. vulgaris_, collected from different areas of Italy. They found that phenolic components significantly prevailed over the rest in all the studied oils. The most common compounds were thymol (46.2-67.5%), carvacrol (5.7-7.3%), and carvophyllene oxide (1.7-7.3%). A predominantly aromatic substance in the composition of the essential oil of garden thymre is the phenol thymol (18.11-55.44%), which is responsible for the typical spicy smell. Thymol is usually accompanied by compounds related to its biosynthesis, its isomer carvacrol (1.00-18.31%), and p-cymene (6.61-25.20%) and \(\gamma\)-terpinene (2.23-10.00%). From the group of monoterepens, linalool (3.72-4.66%), and in smaller quantities (0.5-1.5%), borneol, camphor, limonene, myrcene, \(\beta\)-pinene, trans-sabine hydrate, \(\alpha\)-terpineol, and terpinene-4-ol were found in the composition of the oil. Sesquiterpenes are poorly represented in garden thymre essential oil (\(\beta\)-caryophyllene 5.38-8.47%) [1; 2]. A factor for the different chemical compositions of essential oils is also the season when the plants are harvested [14; 15]. [PERSON] et al. [15] report that the main components in the essential oil of the species _T. vulgaris_ cultivated in Brazil are thymol (38.99-52.92%), p-cymene (14.38-26.58%), and \(\gamma\)-terpinene (10.43-19.09%). Antioxidant activity is determined by the DPPH, ABTS, and FRAP methods. They found that the results varied according to the methods. Thyme essential oils have prominent antimicrobial [12; 13; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26], antioxidant [12; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36], and other biological properties [13; 22; 34]. This is due to the phenols thymol and carvacrol contained in their composition [24; 37; 38; 39; 40]. Due to their characteristic biological properties, thyme essential oils are used in the food industry, medicine, and pharmacy [41; 42; 43; 44; 45]. In Bulgaria, common thymre is a very popular plant, which is mainly found in the wild in fields and the lower parts of mountains. It finds exclusive use in folk medicine, as well as for flavoring various food products. Several cultivars of the species _T.