Microwave-assisted hydrodistillation extraction method

An ethos microwave extractor (1000 W, Frequency 2450 MHz, Milestone, Italy) was used for extracting oil from V. cinerea leaf. The sample (20 g) was placed in a 250 mL conical flask containing distilled water of 200 mL. The flask was placed in the extractor cavity and a condenser was mounted to collect the extracted oil (Fig. S1). The microwave was set at a power level of 500 W for a period of 90 min at 15 min intervals (15, 30, 45, 60, 75, and 90 min). This irradiation was enough to extract the oil in the plant sample. Thereafter, separating funnel was used to separate the oil by adding few drops of dichloromethane. The oil was dried over anhydrous sodium sulphate and stored at 4 °C until further use. The yield of essential oil from V. cinerea leaf was calculated using Eq. (1).