Abstract
Alpinia zerumbet (Pers.) B.L. Burtt & R.M. Smith is an aromatic plant, distributed widely in the Ryukyu Islands, Japan. It has been extensively studied because its essential oil has a variety of biological functionalities. Underwater shock waves consist of instantaneous high pressures that penetrate entire plant cells and selectively destroy the cell walls of leaves and stems by spalling destruction. Therefore, it is expected that exposing leaves to shock waves as a preprocessing step draws more effective extraction of essential oil by subsequent steam distillation. In this study, we prepared A. zerumbet materials that were subjected to underwater shock wave pretreatment, and evaluated its effect on the leaves for steam distillation. With shock wave loading, multiple cracks in the cell walls were observed by scanning electron microscopy. Moreover, the extracted volume of volatile compounds increased with the number of shock wave processing. In particular, the concentrations of camphor and p-cymene in the vapor phase increased more than four times compared with these of untreated leaves. Underwater shock wave processing selectively and effectively destroyed the fiber and/or cell structures. The headspace gas chromatography/mass spectrometry indicated that the volatile components within the structures were easily volatilized.
