Chemical Composition and Biological Activities of Bulgarian Thyme (Thymus callieri Borbás ex Velen) and Summer Savory (Satureja hortensis L.) Essential Oils.

Thyme (Thymus callieri Borbás ex Velen) and summer savory (Satureja hortensis L.) are aromatic plants from the Lamiaceae family widely used in traditional medicine and the food industry. This study provides a comparative analysis of the phytochemical profiles and biological potential of the essential oils (EOs) of these two plant species from Bulgaria. The chemical composition was determined using GC-MS analysis. Biological evaluation included determination of antioxidant activity (DPPH assay), antimicrobial activity (MIC assay), ex vivo anti-inflammatory effects (IL-1β expression in rat stomach smooth muscle preparations), and in vitro antihemolytic activity. GC-MS analysis identified 16 compounds in T. callieri EO, dominated by p-cymene (46.42%) and thymol (35.80%). In contrast, 17 compounds were identified in S. hortensis EO, with carvacrol (58.81%) and γ-terpinene (22.46%) as major constituents. Both EOs exhibited concentration-dependent antioxidant activity, with S. hortensis showing higher radical scavenging potential. In antimicrobial tests, both oils demonstrated broad-spectrum efficacy with MIC values ranging from 0.313 to 2.5 mg/mL. Ex vivo experiments revealed that T. callieri EO significantly increased IL-1β expression, suggesting immune activation, while S. hortensis EO showed a lower effect, indicating higher anti-inflammatory potential. Furthermore, S. hortensis EO demonstrated superior erythrocyte membrane stabilization (antihemolytic activity) compared to T. callieri EO and the reference anti-inflammatory drug Aspirin. In conclusion, the findings highlighted the distinct biological potential of both Bulgarian EOs, suggesting their diverse applicability as natural bioactive agents in the pharmaceutical and food industries.