Views:20 Author:Site Editor Publish Time: 2019-09-01 Origin:Site
Application of low-intensity ultrasonic technology in food field
The qualitative measurement of low-intensity ultrasonic technology used in the food field began in the 1940s, but this technology has only recently attracted the attention of researchers. The application of ultrasonic analysis and measurement technology in the food industry is mainly based on several main characteristic parameters (sound velocity, attenuation coefficient and sound impedance) of measurable ultrasonic waves, which can reflect the physical and chemical properties of food systems (such as composition, texture and rheology). Physical properties). This relationship can be established in two ways. One is to establish a modified curve by establishing the measured ultrasonic characteristic parameters and the physical parameters of the food, and the other way is to theoretically describe the occurrence of the ultrasonic wave through the medium. A qualitative change in the nature of the food system.
1.Determine the thickness of the medium
Ultrasonic equipment can accurately determine the thickness of the medium. Compared with other technologies, ultrasonic measurement of the thickness of the medium is as long as the instrument is close to one end of the sample to be tested. Therefore, when it is difficult to measure the thickness of the sample using conventional techniques, it is convenient to use ultrasonic to measure the thickness. This technique has been used for the determination of the thickness of the chocolate coating in the candy, the thickness of the meat, the thickness of the liquid layer in the can, and the thickness of the eggshell.
2.Detecting foreign matter in foods
In the food processing process, there are often foreign materials such as metal chips, glass fragments and wood chips. Traditional optical inspection techniques cannot be applied to optical non-transparent systems. In this case, ultrasonic detection technology is very fast and convenient. The principle of measurement is that when an ultrasonic pulse is introduced into the sample, the pulse will be reflected back from all the surfaces of the medium encountered. Due to the obvious difference between the impurity and the sound impedance of the product component, the ultrasonic properties are also significantly different, so the impurity can be detected. come out.
3.Determination of flow rate
In many food processing operations, it is important to control the flow rate of food materials. Researchers have developed a series of flow meters for measuring the flow of food materials through pipes, such as flow meters. The range of measurement of ultrasonic flow meters ranges from a few millimeters per second to tens of meters. These ultrasonic flow meters generally measure the average flow rate of the material. Recently developed more sophisticated flow meters can be used to qualitatively determine the cross-sectional state parameters of fluid flow through the pipe. Many ultrasonic flow meters are used to accurately determine the flow rate of different components in a fluid rather than being limited to determining the flow rate of a single fluid.
4.Determination of food composition
The principle of ultrasonic technology for measuring food composition is the difference in ultrasonic properties of different components, such as sound velocity, attenuation coefficient and sound impedance. The greater the difference, the easier it is to identify the composition of the food. This technology has been successfully used to measure the concentration of sugar in various juices and beverages.
5.Determination of the particle size of the dispersed phase
The size of the dispersed phase particles has a significant effect on the physicochemical properties of dispersions such as emulsification, suspension and foam, affecting the stability, appearance and mouthfeel of the system. Compared with the traditional method, the ultrasonic wave can eliminate the pre-treatment of the sample preparation and realize the on-line detection operation when measuring the particle size of the dispersed phase, and is also suitable for the detection of the non-transparent system.
The principle of ultrasonic measurement of the size of the dispersed phase particles is that the scattering occurs when the ultrasonic wave is incident on the system. The scattering effect depends on the concentration and size of the particles. The sound velocity and attenuation coefficient of the ultrasonic wave can be expressed by the degree of scattering. Therefore, data on the particle size of the dispersed phase can be obtained by measuring the speed of sound and the coefficient of attenuation. In fact, the size and concentration of the particles in the emulsion and the suspension can be determined by measuring the frequency, and the distribution of the particle size can be measured by measuring the attenuation coefficient. This technique has been used to determine the size of food system particles such as mayonnaise and margarine.
6.the detection of emulsion stratification
Since the density of the oil is generally lower than the density of water, this causes the droplets in the oil-in-water emulsion to float and stratify on the liquid surface, whereas the droplets in the water-in-oil system, in contrast, cause the liquid to stratify due to precipitation. The application of ultrasonic technology to determine the propagation speed or attenuation coefficient of sound waves in the system can provide important reference data for the determination of product system stability. The appropriate mathematical equations can be used to convert the ultrasonic parameters into the physical and chemical properties of the desired detection system, such as particle concentration and size, thus effectively monitoring the occurrence of foaming and precipitation in complex food systems. This technique has been used to study the stability of milk emulsions, juices, margarines, beer foams and salad creams.
7.Phase transition monitoring
Phase transitions occur primarily because foods contain ingredients that melt or crystallize, such as sugar, oil, and moisture. Since the ultrasonic properties of the melting or crystallization process system change significantly, the phase transition can be monitored using ultrasonic technology.
The ultrasonic velocity of the solid is significantly greater than the liquid, so the speed of the ultrasonic waves increases significantly as the components in the sample crystallize. The speed of the ultrasonic wave is significantly reduced when melted. In practical applications, it is often determined by measuring the wave velocity to determine whether phase separation of mayonnaise or margarine occurs.
8, ultrasonic development technology
This technique is more commonly used in medicine and is also used to study the internal structure of some materials, which are now used in the food industry. There are many literatures and applications in foreign literature, which classify animals. Ultrasonic development technology can also be used to detect the stratification of emulsions and suspensions, to detect the presence of impurities and to determine the degree of crystallization that occurs in foods. Moreover, the cost of ultrasonic developing technology instruments is gradually being lowered, and it is expected to be further utilized in the food industry.