Secondary metabolites and their antioxidant capacity of Caucasian endemic thyme (Thymus transcaucasicus Ronn.) as affected by environmental stress

Environmental factors can influence the yield and biochemistry of medicinal plants playing as natural tools for improvement or limiting herbal productivity and quality under controlled environment conditions. This study investigated the impacts of constant air temperature (15, 20, 25 degrees C) and air humidity (50, 70, 90%) on content, composition, antioxidant capacity and lipid peroxidation potential of essential oil, carotenoids, polyphenols of Thymus transcaucasicus under controlled environment conditions. The metabolite profile of Caucasian endemic thyme was analysed, bioactive compounds were quantified and their health-promoting properties were analyzed in bioassays. In climatic chambers the highest contents of essential oil, carotenoids and polyphenols were 0.553%, 110.8 mg% and 0.550 mM GAE, respectively. The main components of essential oil were borneol, alpha-terpineol, carvacrol, thymol, geraniol, linalool, 1,8-cineole and geranyl acetat. Lutein, zeaxanthin, chlorophyll a, chlorophyll b, alpha-carotene and beta-carotene were the major carotenoids, while polyphenols mainly consisted of phenolic acids and the dominant compound was rosmarinic acid. It was found that the comparatively high air temperature and humidity impacted positively on herbal productivity, while the content and yield of essential oil reached a maximum at high air temperature and low air humidity. 20 degrees C and 50% were found to be more effective for the best recovery of carotenoids and polyphenols, while the second peak of polyphenols was registered at 90% air humidity. The compositions of essential oil, carotenoids and polyphenols were mostly influenced by environmental temperature and humidity with different relationships. The environmental stress had a significant impact on antioxidative capacity and lipid peroxidation potential of carotenoids and polyphenols, while the health-promoting capacity of essential oil was affected to a lesser extent. Such biochemical response to environmental stress is important part of adaptation strategies of herbs and can be used as natural tool for the controlled production of high-quality herbal plant materials.