A Phenological Variation in Essential-Oil Yield and In Vitro Antibacterial Activity of Thymus algeriensis and Thymus capitatus from Tarhuna, Libya

Phenological Variation in Essential-Oil Yield and In Vitro Antibacterial Activity of Thymus algeriensis and Thymus capitatus

Abstract

Background: Phenological development can strongly influence essential-oil (EO) production in aromatic plants, although comparative evidence for Libyan Thymus species remains limited.

Aims: To quantify phenological variation in EO yield of Thymus algeriensis and Thymus capitatus from Tarhuna, Libya, and to describe the in vitro antibacterial activity of the corresponding pooled oils.

Methods: Dried aerial parts collected at vegetative, flowering and post-flowering stages were hydrodistilled for 3 h using a Clevenger apparatus. Three independent hydrodistillations were performed per species × stage combination. Yield was analysed by two-way factorial ANOVA. The three oils from each combination were then pooled and screened by disc diffusion against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 using three technical disc measurements.

Results: Yield was affected by species, stage and their interaction (all p < 0.0001). Flowering produced the highest yield in both species: 1.85 ± 0.05% in T. algeriensis and 3.22 ± 0.10% in T. capitatus. The species × stage interaction was very large (partial η² = 0.942), reflecting a modest flowering increase in T. algeriensis (+13.3% over vegetative) versus a much larger increase in T. capitatus (+62.2%). Mean inhibition zones of pooled oils ranged from 22.67 to 25.33 mm; the largest observed zone was obtained against E. coli with post-flowering T. capitatus oil.

Conclusion: Phenological timing has species-specific consequences for EO recovery, with flowering providing the highest yield under the investigated conditions. Antibacterial patterns did not parallel the yield trajectory. Because oils were pooled before antibacterial testing, activity differences are descriptive and require confirmation using independently tested extraction replicates and quantitative dilution assays.