Ultrasound-assisted extraction technology is a new type of separation technology developed in recent years. Compared with conventional extraction technology, ultrasonic-assisted extraction technology is fast, economical, safe, and efficient. Under the action of the cavitation field, the instantaneous pressure increase and decrease produces a pressure difference between the inside and outside of the cell wall, causing the target extract to be released from the tear, thereby achieving the purpose of extraction. In addition, the thermal and mechanical effects of ultrasonic waves can also promote the enhanced extraction of ultrasonic waves.
At present, in the use of ultrasonic extraction technology, a single frequency is often used for ultrasonic extraction, but a single frequency ultrasonic wave is more likely to generate standing waves, which reduces the cavitation time and cannot maximize the ultrasonic auxiliary effect. In recent years, some scholars have researched a self-focusing ultrasonic transducer that can achieve the superposition effect of two frequencies of ultrasound. Theoretical analysis and experimental results show that the transducer can achieve dual-wave superposition and generate sound scattering effects. The two columns of sound waves generated by the complex frequency transducer can be acoustically scattered, widening the sound field spectrum, and providing a larger range of cavitation nuclei with the opportunity to produce cavitation effects. At present, there is no unified theory on the mechanism of combined ultrasound enhanced leaching, which needs to be studied. Compared with the intermittent ultrasonic extraction, which is more commonly used, continuous extraction has more industrial prospects.
2. Ultrasonic wall breaking and promoting penetration
During the ultrasonic treatment, the cavitation effect releases huge energy, causing the cells to rupture to achieve the purpose of breaking the wall. S. Aparna and MNGupta studied the process of extracting almond oil from almonds. It first used ultrasonic waves with a power of 70W to treat the almond cell wall for 2 minutes at a pH of 4 and a temperature of 40 ° C. This helped the almond cell wall rupture and helped the extraction solvent to interact more effectively with The contact with the target extract shortened the extraction time to 6h and increased the extraction rate by 77%. The effect was obvious.
3. Ultrasound homogenization and emulsification
Use the cavitation of ultrasonic waves in liquids to achieve a homogeneous effect. MLMelissa et al. Used 20kHz ultrasound to treat 28% corn slurry for 3h, with a processing capacity of 10 ～ 28L / min, and the homogenization effect was increased by 2 ～ 3 times compared with the traditional method; observed by scanning electron microscope, ultrasonic treatment greatly reduced corn The particle size of the slurry reduces the particle size from 1200 μm to an average of 361.8 μm, thereby achieving the purpose of homogeneity. S.Kentish et al. Applied phacoemulsification technology to the beverage industry, using
Ultrasonic waves with a frequency of 20 to 24 kHz make the mixture molecules of linseed oil and water form an emulsion with a particle size of 135 nm. The droplet size is proportional to the ultrasonic power, thereby improving the emulsification efficiency.
4. Ultrasonic cutting
In the food industry, ultrasound is also used in food cutting assistance technology. The mechanical and thermal effects of ultrasound affect the contact surface of food cutters, which can change the loss of cutting force on some foods. Susann Zahn et al. Studied the impact of ultrasonic frequency and vertical cutting speed on food cutting quality, controlling a specific cutting speed, and increasing the ultrasonic frequency can increase the workload, but when the maximum cutting speed is reached, 20 ～ 40kHz ultrasonic waves have no effect on it. Significant impact. S. Yvonne et al. Studied the effect of ultrasonic frequency on cutting force and proposed that the power consumption of ultrasonic depends on the amplitude and frequency. Increasing the amplitude increases the processing capacity, but there is a greater power demand. Increasing the ultrasonic frequency can effectively improve the cutting Speed, increase throughput and reduce energy consumption.
5.Ultrasonic atomization spraying
At present, ultrasonic waves are applied to a new packaging technology, namely the ultrasonic-assisted atomization packaging system, which uses high-frequency mechanical motion of ultrasonic waves to atomize and spray the packaging material on the surface of the package to be packaged. K. Wanwimol and Yao-Wen Huang used ultrasonic waves with a frequency of 40 kHz and a power of 130 W to mix chitosan and water at a ratio of 1:10 and mix them with 240 mg / g of encapsulating powder. Emulsify and atomize the surface of tuna oil first. The package has low water content and water activity, and the package appearance is acceptable, which can improve the stability of tuna oil and other oils in industrial applications.
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