Stress amelioration and anti-inflammatory potential of Shiikuwasha (Citrus depressa Hayata) essential oil, limonene, and γ-terpinene

Shiikuwasha (Citrus depressa Hayata) essential oil (SEO) extracted from Shiikuwasha fruit pulp contains two major volatile components, limonene and γ-terpinene (56.56–57.31 and 24.41–24.98%, respectively). In this study, we showed that the aroma streams of SEO, limonene, and γ-terpinene exhibited significant physiological stress amelioration effects in nine healthy female panelists tested in a 30-min visual display task. While SEO administration significantly reduced work errors by 15 min compared to the odorless control condition, the limonene stream reduced work errors only at the first and fourth 5-min intervals, and the γ-terpinene effect lasted only for the initial 5-min. However, γ-terpinene inhalation reduced stress by significantly increasing post-work electrocardiogram R–R interval variability and lowering electroencephalogram beta wave powers at the midline occipital Oz position. Additionally, SEO, limonene, and γ-terpinene displayed anti-inflammatory activity in vitro by suppressing the pro-inflammatory markers NO and IL-1β in BV-2 microglial cells in a dose-dependent manner.