When large-energy ultrasonic waves act on the extraction medium, when the vibration is in a sparse state, the medium is torn into many small holes by the natural product extraction device, and these small holes are instantaneously closed, and instantaneous pressure of up to several thousand atmospheres is generated when closed. , that is, cavitation. The strengthening effect of ultrasonic on the extraction and separation of various components is mainly due to its cavitation.
The extreme pressure generated by the bursting of tiny bubbles in the cavitation causes the rupture of the cell wall and the whole organism to be broken in an instant, shortening the breaking time, and the vibration generated by the ultrasonic waves enhances the release, diffusion and dissolution of intracellular substances. Can significantly improve the extraction efficiency. The ultrasonic fracture process is a physical process in which no chemical reaction occurs and the biologically active material being extracted remains unchanged.
During the cavitation, the tiny bubble nuclei in the liquid oscillate, grow, shrink and collapse under the action of high-intensity ultrasonic waves, and generate high temperature and high pressure around the cavitation bubbles in a very short time of collapse. The strong shock wave and the micro-jet above 400km/h create a new active surface for the peeling, etch and pulverization of the solid surface. This interface effect increases the mass transfer surface area. The turbulence effect generated during cavitation makes the mass transfer boundary layer in the solid-liquid interface thin, resulting in a much faster decrease in the concentration gradient of solute in the interface layer than other methods. The perturbation effect caused by cavitation strengthens the micropore diffusion in the solid-liquid mass transfer process, which enhances the eddy diffusion and accelerates the extraction process. The ultrasonic frequency is increased, the extraction time is prolonged, and the energy absorption effect generated by the ultrasonic field causes the temperature of the extract to rise. Turbulence effects, perturbation effects, interfacial effects, and energy-concentration effects are related to the frequency, power, and temperature of the system. In the natural product extraction process, cell wall breakage, solute diffusion and equilibrium velocity are related to the ultrasonic power per unit area, and both of them will affect the extraction efficiency and recovery rate. Therefore, low-frequency high-power ultrasound is generally used.
Although ultrasonic extraction is very effective in the preparation of small samples in the laboratory and has been widely used, especially in the processing of analytical samples, its rapid and efficient characteristics have been widely recognized, but the range and intensity of the ultrasonic field limit each time. The amount of material processed, the lack of effective engineering amplification methods and methods limit its application in large-scale production.