Dissolved Oxygen Removal From Aqueous Phase of Prepared Thyme Essential Oil in Water Nanoemulsions and Assessment of Their Physico-Chemical Properties and Antibacterial Activities.

Thyme essential oil (TEO), due to its valuable compounds such as thymol and carvacrol, has high antioxidant and antimicrobial activities. But, its applications in aqueous system limits due to its nonpolar nature. In the present study TEO in water naonoemulsions (NEs) were prepared using pressurized water (PW). Results indicated that, the produced NEs had droplet size, polydispersity index (PDI), zeta potential, and antioxidant activity of 78 nm, 0.136, -19.2 mV, and 31.3%, respectively. Due to the oxygen sensitivity of TEO, effectiveness of three different dissolved oxygen (DO) removal techniques, based on nitrogen purging, sonication, and boiling of aqueous phase were evaluated. Results indicated that DO in the aqueous phase was 9.25 ppm and decreased to 0.61 ppm, using DO removal technique based on nitrogen purging. Results revealed that, sonication was more efficient DO removal method and prepared TEO NE by this pretreatment had droplet size, PDI, zeta potential, and antioxidant activity to 52 nm, 0.122, -20.4 mV, and 48.4 %, respectively. Furthermore, this prepared NE had enhanced bactericidal activity against Streptococcus mutans and Escherichia coli. It can be concluded that by removing DO from aqueous phase, TEO NEs with significantly higher biological activities can be prepared for various applications.