The main goal of the research was to optimize microwave-assisted simultaneous distillation and extraction (MA-SDE) using response surface methodology
(RSM), based on Box-Behnken design (BBD). A process was designed to extract the essential oil from the leaf sheath of Siam cardamom. The experimental
data were fitted to quadratic equations, and the experiment conditions for optimal extraction of 1,8-cineole were extraction time 87.68 min, material-towater
ratio 1:13.18 g/mL and microwave power 217.77 W. Under such conditions, the content of 1,8-cineole was 157.23 +/- 4.23 mu g/g, which matched with
the predicted value. GC-MS results indicated the presence of predominant oxygenated monoterpenes including 1,8-cineole (20.63%), iso-carveol (14.30%),
cis-p-mentha-1(7),8-dien-2-ol (12.27%) and trans-p-2,8-menthadien-1-ol (9.66%), and oxygenated contents were slightly higher in the MA-SDE and
extraction compared to usual SDE. In addition, the essential oil extracted by MA-SDE exhibited strong antibacterial effects against the tested Gram-positive
bacteria. Scanning electron micrographs provided more evidence of destruction of the leaf sheath treated by MA-SDE. Conclusively, microwave-assisted
simultaneous distillation and solvent extraction appear to be an effective technique for the separation of essential oils enriched 1,8-cineole from Siam
cardamom leaf sheath in a shorter time.