Variation of Essential Oil Composition and Antioxidant Activity in Aerial Parts of Stachys Schtschegleevi Sosn at Different Growing Stages

Stachys schtschegleevii Sosn is an endemic medicinal plant that belongs to the Lamiaceae family and is mainly grown in the Northwestern parts of Iran. This plant contains essential oils that are medicinally valuable with very few available information on them. In this study, the aerial parts of S. schtschegleevii were collected at different plant growth stages (Vegetative, flowering, seed set and seed ripping) and their essential oil (EO) compositions were determined at each stage separately. In order to determine EO contents in S. schtschegleevii, the hydrodistillation method was used. The chemical compounds were then analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) methods in all studied stages. The highest EO yield was observed in the flowering stage (0.25 %). Significant variations were detected in EO compounds during various stages of growth. In vegetative stages, spathulenol (19.63 %), germacrene-D (11.3 %), α-pinene (7.8 %), α-cadinol (5.8 %) and β-eudesmol (7.2 %) were the major components; while in the flowering stages, the major compounds were α-pinene (15 %), germacrene-D (12.6 %), spathulenol (12 %) and β-pinene (5.9 %). α-pinene (17.9 %), α-cadinol (12.4 %), germacrene-D (11.6 %) and spathulenol (6.5 %) were the prominent constituent of the essential oil during seedset stage. Finally, when the seeds ripened, the main components of EO were reported as α-pinene (19.5 %), spathulenol (14.68 %), α-cadinol (10.5 %) and germacrene-D (5.6 %). In the seed ripping stage, monoterpene hydrocarbons recorded as the most dominant component (37.0 %). In the flowering stage, this component was as low as 15.4 % where the highest compound was α-pinene that followed by oxygenated sesquiterpenes. Also, the highest total phenol accumulation (81.70 mg GAE/g DW) and total flavonoid (8.70 mg QE/ g DW) were observed in the flowering stage which is also considered as the stage with maximum antioxidant activity. Based on the results, the flowering stage is the best harvesting time for S. schtschegleevii plants to produce EO for both food and pharmaceutical purposes.