Phenological changes to the chemical composition and biological activity of the essential oil from Moroccan endemic thyme (Thymus maroccanus Ball)

The chemical composition, antioxidant and antimicrobial activities of essential oils isolated by hydrodistillation from the aerial parts of wild endemic Moroccan Thymus maroccanus at different developmental stages (vegetative, flowering and post-flowering) were evaluated. The yield of essential oils (v/w%) based on dry weight at different stages were: vegetative (2.14%), flowering (leaves: 1.80%; flowers: 3.46%), and post-flowering (leaves: 0.98%; post-flowers: 2.46%). Analysis of the essential oils by GC/MS revealed the presence of 28 components represented mainly by monoterpenes, both oxygenated (59.4-79.4%) and hydrocarbons (14.3-34.2%). The ranges of major constituents were as follow: carvacrol (14.1-77.6%), p-cymene (3.5-7.9%), γ-terpinene (3.8-6.6%) and α-pinene (1.2-7.8%). Leaves at post-flowering stage also contained a significant amount of borneol (16.3%) and thymol (27.8%). Essential oils obtained from flowering stage showed the highest antioxidant activity as measured by DPPH free radical scavenging ability, reductive potential and β-carotene/linoleic acid assays with IC50 values ranging from 61.48±1.58μg/mL to 182.86±2.84μg/mL for leaves and from 63.81±1.96μg/mL to 129.93±6.16μg/mL for flowers. The essential oils were also screened for antimicrobial activity against seven bacteria of significant importance for food hygiene and four pathogenic fungal strains. The results indicated that Candida strains were the most sensitive among the microorganisms tested (MIC values of 0.12-0.25mg/mL) followed by Gram positive and Gram negative bacterial strains, with the Gram-negative Pseudomonas aeruginosa being the most resistant strain. The maximum antimicrobial activity was observed with oils obtained from the vegetative and flowering stages, which therefore represent the optimal harvesting times of this plant for application in the pharmaceutical and food industries.