The mechanism of ultrasonic extraction

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The mechanism of ultrasonic extraction Ultrasound extraction technology (Ultrasound Extraction, UE) is the latest and more mature method that has been applied to the extraction and separation of active ingredients in Chinese herbal medicines in recent years. Ultrasound refers to electromagnetic waves with a frequency of about 20 kilohertz to 50 megahertz. It is a mechanical wave that requires an energy carrier—a medium—to propagate. There is an alternating period of positive and negative pressure during the transmission process of ultrasonic waves. When in the positive phase, it squeezes the molecules of the medium and increases the original density of the medium. ； In the negative phase, the medium molecules are sparse and discrete, and the medium density decreases. In other words, ultrasonic waves do not polarize the molecules in the sample, but produce acoustic cavitation between the solvent and the sample, leading to the formation, growth, and explosion compression of bubbles in the solution, thereby dispersing the solid sample, increasing the contact area between the sample and the extraction solvent, and increasing the mass transfer rate of the target substance from the solid phase to the liquid phase. In terms of industrial applications, the use of ultrasonic waves for cleaning, drying, sterilization, atomization and non-destructive testing is a very mature and widely used technology. The principle of ultrasonic extraction The superiority of ultrasonic extraction of Chinese medicinal materials is based on the special physical properties of ultrasonic waves. It mainly uses fast mechanical vibration waves generated by piezoelectric transducers to reduce the force between the target extract and the sample matrix to achieve solid-liquid extraction and separation. (1) Accelerate the movement of medium particles. When ultrasonic waves with a sound frequency higher than 20 KHz propagate in a continuous medium (such as water), according to the Huygens wave principle, the wave front of the propagation will cause the movement of medium particles (including particles with important active components of medicinal materials), causing the movement of medium particles to acquire huge acceleration and kinetic energy. The acceleration of a particle is generally calculated to be more than two thousand times the acceleration of gravity. Because the medium particles act on the particles of the medicinal ingredients in the medicinal materials using ultrasonic energy, they gain huge acceleration and kinetic energy, and quickly escape from the matrix of the medicinal materials and become free in the water. (2) Cavitation. The propagation of ultrasonic waves in liquid media produces a special "cavitation effect". The "cavitation effect" continuously produces countless micro-cavitations with internal pressures reaching thousands of atmospheres and continuously "explodes" to produce microscopically powerful shock waves that act on the Chinese medicinal materials, causing the Chinese medicinal materials to be "bombarded" to escape, and the medicinal matrix is ​​continuously eroded, and the medicinal ingredients that do not belong to the plant structure are continuously separated. Accelerate the leaching and extraction of effective plant ingredients. (3) The vibration homogenization (Sonication) of ultrasonic waves causes uniform effects on each point in the sample medium, making the entire sample extraction more uniform. To sum up, under the action of ultrasonic field, the medicinal substances in Chinese herbal medicines not only gain their own huge acceleration and kinetic energy as medium particles, but also gain powerful external impact through the "cavitation effect", so they can be separated with high efficiency and fully. Characteristics of ultrasonic extraction: It is suitable for the extraction of active ingredients of Chinese medicinal materials. It is a new method and new technology for Chinese medicine pharmaceuticals that completely changes the traditional boiling and alcohol precipitation extraction method. Compared with boiling and alcohol precipitation processes, ultrasonic extraction has the following outstanding features:: (1) No need for high temperature. Ultrasonic wave-enhanced extraction at a water temperature of 40°C - 50°C, without boiling at high temperatures, will not destroy certain medicinal ingredients in Chinese medicinal materials that are thermally unstable and easily hydrolyzed or oxidized. Ultrasonic waves can cause plant cells to break down and improve the efficacy of traditional Chinese medicine. (2) Normal pressure extraction, good safety, simple and easy operation, and convenient maintenance. (3) High extraction efficiency. Ultrasonic-enhanced extraction can achieve the best extraction rate in 20 to 40 minutes, and the extraction time is only one-third or less of that of boiling and alcohol precipitation methods. The extraction is sufficient, and the extraction volume is more than twice that of traditional methods. According to statistics, ultrasonic waves work very efficiently at 65 to 70 degrees Celsius. The active ingredients of Chinese herbal medicine plants are basically not destroyed when the temperature is within 65 degrees Celsius. After adding ultrasonic waves (at 65 degrees), the extraction time of active plant ingredients is about 40 minutes. The cooking time of the steaming method often takes two to three hours, which is more than three times the time of ultrasonic extraction. Each jar is extracted three times, and basically more than 90% of the active ingredients can be extracted. (4) It has broad spectrum. It has wide applicability, and most of the various components of Chinese medicinal materials can be extracted by ultrasonic extraction. (5) Ultrasonic extraction has little relationship with the properties (such as polarity) of the solvent and the target extract. Therefore, there are many types of extraction solvents to choose from and a wide range of target extractables. (6) Reduce energy consumption. Since ultrasonic extraction does not require heating or the heating temperature is low and the extraction time is short, it * * Reduce energy consumption. (7) The processing volume of medicinal raw materials is large, doubled or several times higher, and there are few impurities, and the active ingredients are easy to separate and purify. (8) The extraction process has low cost and significant comprehensive economic benefits. ； (9) Ultrasonic waves have a certain bactericidal effect and ensure that the extraction liquid does not deteriorate easily. At present, the ultrasonic extraction instrument widely used in laboratories transmits the ultrasonic waves generated by the ultrasonic transducer (Transducer) through the medium (usually water) and acts on the sample. This is an indirect mode of action, and the intensity of the sound vibration is low, so * * Reduced ultrasonic extraction efficiency. In addition, the ultrasonic generators usually used in laboratories are relatively powerful.