Hydrodistillation, comparative analysis and optimization of essential oils from Thymus schimperi R, Thymus serrulatus R, and Ocimum lamiifolium Hochst ex Benth

Essential oils are valuable natural products that are currently popular worldwide due to their positive effects on human health and their significant role in preventing and curing diseases. The increasing prevalence of antibiotic-resistant pathogens poses a major global health challenge, limiting the effectiveness of conventional antimicrobial therapies. Medicinal plants such as Thymus schimperi R., Thymus serrulatus R., and Ocimum lamiifolium Hochst. ex Benth., are traditionally used for treating infections and are known to produce essential oils rich in bioactive compounds with antimicrobial activities. Investigating the essential oils from these plants provides a potential alternative. This study focused on the parametric optimization of essential oil extraction from the leaves of T. schimperi R., T. serrulatus R., and O. lamiifolium Hochst. ex Benth., collected from the Ankober and Tarmaber Districts, North Shewa Zone, Amhara Region, Ethiopia, using hydrodistillation method. T. schimperi R., T. serrulatus R., and O. lamiifolium Hochst. ex Benth., leaves were gathered, authenticated, dried, and ground into three different particle sizes (0.25, 2, and 4 mm). Using a Clevenger apparatus, essential oils were hydrodistilled at 95 °C for specified extraction durations (30, 60, and 120 min). Particle size and extraction time were optimized using a Taguchi experimental design, and oil yield was determined gravimetrically. Every experiment was conducted in triplicate, and factors influencing yield were evaluated for significance using ANOVA (p < 0.05). The maximum yield of essential oil was obtained from T. schimperi R., (3.05%, w/w) with particle size of 2 mm and extraction time of 60 min at constant sample loading (10 g) and volume of water (350 mL). Of the parameters investigated, particle size had the most significant influence on essential oil yield. This study indicates that while pure and sufficient amounts of essential oils extracted within a short timeframe, the yield will eventually decrease due to evaporation of the extracted oils.