Year-round yield of essential oil of Vitex negundo and its chemical constituent analysis

Leaves of 3 years old Vitex negundo L., were harvested and subjected to steam distillation to extract essential oil. Both leaves biomass and yield of essential oils were the highest during May to September. The extraction rate ranged from 0.5–0.6%, higher than the reported 0.35% by Mainland China. Consistent with previous reports, Caryophyllene is one major constituent occupy approximately 30–38% of total essential oil. In contrast, Guaiene is a minor constituent in previous reports but accounts for 50% of the total essential oil in our study. The results reveal that major constituents of essential oils of Vitex negundo L. can vary substantially among different months and countries of origin. The quality and functions of essential oil of Vitex negundo L. are worth of further investigation.