Principle of ultrasonic extraction
Ultrasound (frequency between 20 kHz and 1 MHz) is a mechanical wave that requires an energy carrier-medium to propagate.
The principle of ultrasonic extraction is to use the cavitation effect, mechanical effect and thermal effect of ultrasonic waves to extract the chemical composition of the sample by increasing the moving speed of the medium molecules and increasing the penetrating power of the medium. The following is an example of Chinese herbal medicine:
(1) Cavitation effect Generally, some microbubbles are dissolved more or less inside the medium. These bubbles vibrate under the action of ultrasonic waves. When the sound pressure reaches a certain value, the bubbles increase due to the directed diffusion, forming a resonant cavity. And then suddenly closed, this is the cavitation effect of the ultrasound. When the bubble is closed, it generates pressure of several thousand atmospheres around it, forming a micro-shock, which can cause the plant cell wall and the whole organism to rupture, and the entire rupture process is completed in an instant, which is favorable for the dissolution of the active ingredient.
(2) Mechanical effect The propagation of ultrasonic waves in the medium can cause the medium particles to vibrate in their propagation space, thereby enhancing the diffusion and propagation of the medium, which is the mechanical effect of the ultrasonic waves. Ultrasonic waves generate a kind of radiation pressure in the process of propagation, which propagates along the direction of sound waves, which has a strong destructive effect on the material, which can deform the cell tissue and denature the plant protein. At the same time, it can also give the medium and the suspension different accelerations. And the velocity of the medium molecules is much faster than the velocity of the suspension molecules. Thereby, friction is generated between the two, which can depolymerize the biomolecules, so that the active components on the cell wall dissolve in the solvent more quickly.
(3) Thermal effect Like other physical waves, the propagation of ultrasonic waves in a medium is also an energy propagation and diffusion process. That is, during the propagation of ultrasonic waves, the acoustic energy is continuously absorbed by the particles of the medium, and the medium will absorb it. All or most of the energy is converted into heat energy, which leads to an increase in the temperature of the medium itself and the medicinal tissue, which increases the dissolution rate of the active ingredient of the drug. Since the increase in the internal temperature of the drug tissue caused by the absorption of the acoustic energy is instantaneous, the biological activity of the extracted component can be kept constant.