Abstract:To investigate the optimal extraction processes，chemical compositions，and antioxidant and antibacterial activities of tea tree essential oil and thyme essential oil，ultrasound-assisted water distillation was used to extract the two essential oils.Extraction yield was used as the optimization index，and single-factor experiments combined with response surface methodology were applied to optimize the extraction processes.Gas chromatography-mass spectrometry （GC-MS） and a total antioxidant capacity （T-AOC） assay kit were used to identify the chemical components and determine the in vitro total antioxidant activities of the two essential oils，respectively.The antibacterial activities were evaluated using three common pathogenic bacteria as test strains.The results showed that the optimal extraction conditions for tea tree essential oil were a sodium chloride concentration of 6.13%，a liquid-to-material ratio of 10∶1 （mL/g），and an extraction time of 1.1 h，with an extraction yield of （2.53±0.45）%.The optimal extraction conditions for thyme essential oil were a sodium chloride concentration of 4.18%，a liquid-to-material ratio of 15.04∶1 （mL/g），and an extraction time of 1.1 h，with an extraction yield of （1.48±0.21）%.A total of 17 compounds were identified in tea tree essential oil，and the main volatile components were olefins and alcohols，accounting for 59.27% and 37.84%，respectively，phenolic compounds were not detected.A total of 22 known compounds were identified in thyme essential oil，mainly olefins，phenols，and alcohols，accounting for 75.93%，14.03%，and 6.69%，respectively.Both tea tree essential oil and thyme essential oil exhibited good antioxidant activity with concentration dependence，and the higher contents of phenolic and olefinic compounds conferred stronger antioxidant activity to thyme essential oil.The inhibition zone diameters of the two essential oils ranged from 16.77 mm to 26.45 mm，the minimum inhibitory concentrations ranged from 0.182 3 mg/mL to 5.833 3 mg/mL，and the minimum bactericidal concentrations ranged from 0.364 6 mg/mL to 11.666 7 mg/mL，indicating that tea tree essential oil and thyme essential oil possessed significant broad-spectrum antibacterial activity.