Extraction of essential oil from Aloysia citriodora Palau leaves using continuous and pulsed ultrasound: Kinetics, antioxidant activity and antimicrobial properties

The impact of continuous and pulsed ultrasound pre-treatments (15, 30 and 45 min) followed by conventional hydrodistillation on the characteristics of extracted essential oils (EOs) from dried leaves of Aloysia citriodora Palau was evaluated for the first time. Chemical composition of EOs, antibacterial and antioxidant activities, as well as the contents in heavy metals (iron, copper, lead, arsenic, and cadmium) were determined. Pretreating the leaves with ultrasound (continuous and pulsed), before hydrodistillation, resulted in shorter extraction time (93.81-121.16 min) and higher extraction yields (2.8 (v/w) %) (p < 0.05), compared to the non-sonicated leaves (extraction time: 153.52 min; yield: 2.6 (v/w) %). Relatively high concentrations of geranial (23.24-26.84%) and neral (16.55-17.45%) in the EOs, regardless of the mode of extraction, were measured. Nevertheless, the recovery of all components was improved using ultrasound pretreatment. The antioxidant and antibacterial activities were strengthened in the ultrasonic-assisted extraction process (both continuous and pulsed ultrasound). No measurable quantity of Pb, As and Cd was detected. Higher growth inhibition for bacteria (p < 0.05), as well as the higher free radical scavenging activity (p < 0.05), was observed for the EOs extracted from the hydrodistillated leaves pretreated during 45 min using ultrasound.