Improved yield and antioxidant activity of essential oil from Alpinia zerumbet (Zingiberaceae) leaves by underwater shockwave pretreatment

The aromatic perennial plant Alpinia zerumbet (Pers.) Burtt & Smith (Zingiberaceae) is widely distributed in the tropical and sub-tropical regions of Japan, from southern Kyushu to the Ryukyu Islands. Its essential oil has a distinct aroma and antioxidant activity but is expensive due to low extraction efficiencies. Applying underwater shockwave pretreatment to A. zerumbet leaves is expected to enable more effective essential oil extraction during subsequent steam distillation. Thus, we subjected A. zerumbet leaves to shockwave pretreatment and analyzed its effects on the essential oil yield and components. Multiple cracks formed in the cell walls via spalling destruction induced by the shockwaves, creating permeation pathways that improved the passage of water vapor and greatly increased the essential oil yield. Moreover, the pretreatment increased the antioxidant activity of the essential oil and its water extract. Underwater shockwave processing selectively and effectively destroyed the fiber and/or cell structures of the leaves, resulting in efficient essential oil extraction. This novel process has the potential for application to many extraction processes, such as the extraction of compounds from medicinal plants. The dynamic control of instantaneous high pressures based on underwater shockwaves could pave the way for a new field of industrial technology.