Abstract: The optimum extraction conditions of Thymus dahuricus Serg. essential oil by microwave method and the activity of the main components were explored by orthogonal design experiment. The extraction speed and components of essential oil extracted by microwave method was compared with that by steam distillation method. The antioxidant and antimicrobial activities of essential oils extracted by microwave method were also evaluated. The results showed that the optimal parameters were determined as follows:soaking time of 3 h, solid-liquid ratio of 1:1 (g:mL), extraction time of 40 min, microwave power of 540 W. Under this condition, the extraction ratio of essential oil is 1.04%. The main components of essential oil extracted by microwave method were thymol (52.52%), α-terpinene (12.72%) and p-cymene (8.24%), which was consistent with those obtained by conventional steam distillation extraction. The results of antioxidant activity evaluation showed that among the main components, thymol had the strongest DPPH·scavenging activity (IC₅₀=473.63 mg/L) and the highest β-carotene inhibition rate (IC₅₀=250.91 mg/L). Among the three main components, only the p-cymene had no antioxidant activity. In vitro antimicrobial experiments showed that among three main components of T. dahuricus. essential oil thymol had the strongest antimicrobial activity and was followed by α-terpinene. p-Cymene showed no inhibitory activity on all tested strains. Thymol showed the strongest inhibitory activity against Bacillus subtilis among all tested strains with the diameter of inhibitory zone of 16.85 cm and the minimum inhibitory concentration (MIC) of 0.23 g/L.

Key words: T. dahuricus Serg., essential oil, microwave method, antioxidant, antimicrobial