Seasonal variation of Thymus hyemalis Lange and Spanish Thymus vulgaris L. essential oils composition

Thymus hyemalis L. and Spanish Thymus vulgaris L. shrubs are characterized by a large chemical intraspecific variability among he plants. This fact makes it difficult to detect real changes occurring in their essential oil composition during the vegetative cycle. ased on this, the clones of T. hyemalis and Spanish T. vulgaris were used in this present work to monitor seasonal variations in the omposition of the essential oil. Shrubs were harvested at five different phenological stages during the vegetative cycle. The volatile rofile of the essential oil samples was determined by capillary GC/MS analyses. This technique identified 99 and 98 components n T. hyemalis and T. vulgaris essential oils, respectively. For the Spanish T. vulgaris essential oil, the major components quantified were 1,8-cineole, followed by terpenyl acetate, borneol, inalool, -pinene, -terpineol, and camphor. With respect to the concentrations of some of the most abundant components, the id-vegetative stage seems to be the most appropriate harvesting time for this species. Cineol, borneol, monoterpenic hydrocarbons, nd camphor exhibited their maximum relative concentrations at this phenological stage. In contrast, terpenyl acetate, -terpineol, nd linalool, probably components that are associated with the fresh aroma in the oil, were mostly concentrated from full bloom to dvanced fruit formation. Correlations were detected among the concentrations of the most abundant components in this essential il. Thus, terpenyl acetate and cineol concentrations varied during the entire vegetative cycle. The same behaviour was observed etween sabinene and linalool. For the T. hyemalis, the thymol, which defines the chemical type and the essential oil quality, and its precursors -terpinene nd p-cymene, showed synchronized patterns of variation during the entire vegetative cycle. In this way, the maximum relative oncentration of -terpinene, a precursor of p-cymene, was achieved at the full bloom (FB) phenological stage that coincided with he minimum concentration detected for p-cymene, a precursor of thymol. However, the maximum relative concentration of thymol as detected at full bloom/at the beginning of fruit maturation (FB–FR). From these observations, we can conclude that between B and FB–FR stages could be the period beyond which the sequence -terpinene→ p-cymene→ thymol begins. On the other and, the essential oil exhibited the highest amount in alcohols, ketones, and esters at the vegetative stage. 2006 Elsevier B.V. All rights reserved.