Objective  Thuja koraiensis is a kind of precious economic tree species with fragrance, ornamental and medicinal functions and its essential oil has good antibacterial activity. In order to provide technical scientific basis for the development and utilization of T. koraiensis, we studied the optimization of extraction process, component analysis and antibacterial activity of essential oil from branches and leaves of T. koraiensis.

  Method  The essential oil from the branches and leaves of T. koraiensis was extracted by steam distillation, and the single factor experiment was carried out. The extraction process of the essential oil from the branches and leaves of T. koraiensis was optimized by orthogonal test and response surface methodology. The chemical constituents were analyzed by GC-MS. The antibacterial activity of the essential oil was detected by filter paper and plate coating methods.

  Result  The single factor experiment showed that when the liquid-solid ratio was 7.0 mL/g, the mass fraction of NaCl was 2.0%, the distillation time was 2.0 h, the storage condition was fresh, the extraction rate of essential oil was high. The orthogonal test showed that the optimal combination of the factors was distillation time of 2.0 h, liquid-solid ratio of 7.0 mL/g, NaCl mass fraction of 2.0%. And under the condition, the extraction rate of essential oil was 4.2%. The response surface optimization method showed that the optimal combination was liquid-solid ratio of 6.9 mL/g, distillation time of 2.7 h, NaCl mass fraction of 2.6%. Under the condition, the extraction rate of essential oil was 4.3%, while the actual ate from the experiment was 4.4%, which means that they fit well. From GC-MS analysis, 48 kinds of compounds were detected, accounting for 93.79% of the total, in which the highest was carvyl acetate. There were 17 alkenes, 15 alcohols, 6 esters, 5 ketones and 5 phenols, which accounted for 26.79%, 25.40%, 28.47%, 11.84% and 1.11% of the total, respectively. The diameters of bacteriostatic circle against Staphylococcus aureus, Bacillus subtilis and Escherichia coli were 13.28, 12.04 and 12.94 mm, respectively. The minimum inhibitory concentration (MIC) of the branches and leaves of T. koraiensis to Staphylococcus aureus was 0.005 μg/L, and to Bacillus subtilis and Escherichia coli was 0.010 μg/L.

  Conclusion  The research on the best technology of extracting the essential oil from Thuja koraiensis branches and leaves by steam distillation not only saves the amount of solvent, shortens the distillation time, but also ensures the extraction rate, which is beneficial to the follow-up research and has a certain reference to the production of enterprises. The essential oil from Thuja koraiensis branches and leaves has obvious antibacterial effect and great development potential, so it is recommended for collection and utilization.