Seasonal variation of Thymus piperella L. essential oil composition. Relationship among γ-terpinene, p-cymene and carvacrol

Abstract

ABSTRACT A wild population of Thymus piperella L. was monitored for two years in order to correlate phenological stages and meteorological data with yield and, essential oil (EO) composition. The plant material was extracted by hydrodistillation and the EO was submitted to GC-MS and GC-FID analysis. To achieve reliable quantification, relative response factors were applied. The results showed a progressive increase in the proportion of carvacrol according to the sunlight duration and temperature increase, until reaching a maximum at the beginning of flowering stage (52.9 % and 41.0 % in 2018 and 2019, respectively). A simultaneous decrease was found in the amount of p-cymene (8.2 % and 12.8 % respectively) in the same stage, whereas -terpinene showed a similar evolution to that observed for carvacrol but with lower values (3.3 % - 14.6 %). From statistical analysis, significant changes in the relative proportions of carvacrol and its metabolic precursors: γ-terpinene and p-cymene were found. They have been explained based on the proposed metabolic pathways in the literature. On the other hand, when relating the changes in the EO profiles with rainfall data, a strong influence of the water supply on the evolution of the chemical composition was observed.