Sequential ultrasound-microwave assisted extraction as a green method to extract essential oil from Zataria multiflora

Sequential ultrasound-microwave associated extraction (SUMAE) is a combination of ultrasound waves and microwaves energies in which ultrasonic extraction is used as a pretreatment. It was performed to extract essential oil from Zataria multiflora. The extraction conditions were optimized by response surface methodology (RSM) and Central Composite Design (CCD). The antioxidant and antibacterial activities of the extracted essential oil were investigated. Moreover, the results were compared with microwave associated extraction (MAE) method in terms of process yield, chemical composition, antioxidant activity and environmental impacts. The results show that the optimal conditions were ultrasound power of 150W, microwave power of 800W, and extraction time of 12min. Under these conditions, the yield of the extracted essential oil was 0.812%, which was higher than that obtained by MAE method (0.6%). Regarding environmental impacts, the quantity of carbon dioxide emission was lower in case of SUMAE method (0.25kg) compared to MAE method (0.54kg). This is also true for energy consumptions, which were 0.3125kWh and 0.675kWh for performed SUMAE and MAE, respectively, at the same power level. Furthermore, antioxidant activity of essential oil extracted by SUMAE was higher than that of MAE. Generally, the SUMAE not only did not damage the antioxidant properties, but also improved it and had less environmental damage. Consequently, it can be introduced as a green and safe method for the extraction of essential oils from Zataria multiflora.