|Baldwin, Elizabeth - Liz|
Submitted to: International Conference on Industrial Crops and Rural Development Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/30/2004
Publication Date: N/A
Technical Abstract: Thymus hyemalis L. and Spanish Thymus vulgaris L. shrubs are characterized by a great chemical intraspecific variability among plants. This fact makes it difficult to detect real changes happening in their essential oil composition during the vegetative cycle. Based on this, in the present work, clones of T. hyemalis and T. vulgaris were used to monitor real seasonal variations in the composition of the essential oil. Shrubs were harvested at five different phenological stages during the plant vegetative cycle. Capillary GC/MS analysis was used to determine the volatile profile of the essential oil samples. This technique allowed for the identification of 99 and 98 components in T. hyemalis and T. vulgaris essential oils respectively. Regarding Spanish T. vulgaris essential oil, major components quantified were cineol, followed by terpenyl acetate, borneol, linalool, ß-pinene, a-terpineol and camphor. With respect to the concentrations of some of the most abundant components, the vegetative stage seems to be the most adequate harvesting time for this species. Cineol, borneol, monoterpenic hydrocarbons and camphor exhibited their maximum concentrations at this phenological stage. Nevertheless, terpenyl acetate, a-terpineol, and linalool, probably components that are associated with a fresh aroma in the oil, showed their greatest concentrations from full bloom to advanced fructification. No correlations were detected among concentrations of the most abundant components in this essential oil. In T. hyemalis, thymol, which defines the chemotype and the essential oil quality, and its precursors gamma-terpinene and p-cymene showed synchronized patterns of variation during the whole vegetative cycle. In this way, the minimum relative concentration of a-terpinene, a precursor of p-cymene, was achieved at the phenological stage of fructification (F), coinciding with the maximum concentration detected for p-cymene, a precursor of thymol. However, the maximum relative concentration of thymol was detected at the phenological stage of full bloom/beginning of fructification (FB-FR). From this it can be concluded that FB-FR could be the point beyond which the sequence gamma-terpinene to p-cymene to thymol begins. On the other hand, at the vegetative stage the essential oil exhibited the highest richness in alcohols, ketones and esters.