1、 Overview
Microwave sterilization yes Microwave heating technology The extension of function is manifested in the changes and reactions of biological cell physiological activities after the interaction between microwave, organism and its basic unit cell.
Compared with pasteurization in food and other industries, experimental data show that microwave sterilization has the following significant characteristics:
⑴ Under the same sterilization temperature, the required sterilization time is short; Under the same sterilization conditions, the temperature of bacteria death is relatively low.
(2) It can implement overall sterilization on the sterilized material table at the same time. It can greatly shorten the sterilization cycle and ensure the consistency of sterilization process.
2、 Analysis of microwave sterilization mechanism
As a result of the action of microwave on organisms, organisms as polar media absorb microwave energy and produce two effects: thermal effect and non thermal effect (also known as biological effect). Both of these effects will affect the changes and reactions of biological activities. The thermal effect of microwave on the organism is that the organism absorbs microwave energy and converts it into heat energy (heat) in the body, which increases its own temperature, resulting in thermal denaturation and coagulation (>50 ℃) of the protein that makes up the organism. The consequence will kill bacteria, which is the theoretical basis of pasteurization. As far as the thermal effect of microwave on organisms is concerned, this is the same as the pasteurization effect. However, the impact of microwave radiation on organisms goes beyond this point.
1. Physical environment of microwave sterilization
Microwave radiation has a two-way effect on the interaction of organisms. If the microwave dose exceeds the tolerance threshold of the organism (which can be the whole or a local sensitive part), it will cause harm to the organism. However, if it is below the threshold value, microwave radiation can activate and catalyze the physiological activities of organisms.
Philosophically, the sterilization process is to create a man for the environment, so that bacteria can be affected in such an environment to achieve the purpose of killing bacteria that is not conducive to their survival. Pasteurization creates an artificial environment, which is a thermal field (or temperature field), allowing the proteins that make up bacteria to coagulate and terminate their lives when heated.
Pasteurization environment is physical. Different sterilization temperatures indicate that the bacteria are killed in the temperature field with different heat levels, which reflects the different heat resistance of the killed bacteria or spores.
There are three physical environments for microwave sterilization: one is the thermal temperature field, and the other is the electromagnetic force with high frequency. It is the effect of two physical fields on microorganisms, in which the sterilization of electromagnetic force field is the leading role.
2. Exploration of microwave sterilization mechanism
The mechanism of microwave sterilization is as follows.
(1) Response statement means that the response of biological system to electromagnetic field under certain conditions interferes with the normal biological activity of bacteria, resulting in their death. This statement can be supported by the following experimental facts. The "cell ion channel" and its specific function discovered by Erwin Neer and Bert Zuckerman, two cell physiologists of Max Planck Institute in Germany, who won the 1991 Nobel Prize in biology or medicine, can vividly explain the cause of bacterial death. The experiments of the two scholars recorded the special ion channel currents and
Its changes indicate that external interference factors (such as cross surface magnetic field) will prevent the opening and closing of ion channels that cells rely on to exchange substances with the outside world to maintain normal physiological activities, thus resulting in abnormal cell physiological activities.
⑵ Polarization refers to the phenomenon that cells, as a medium, show polarization in the cross surface electromagnetic environment.
That is to say, with the change of the polarity of the external alternating electromagnetic field, the induced even moment of the cell is subjected to the torque to generate rotation and friction heat in alternate directions. At the same time, the external electric field changes the permeability of cell membrane, leading to the breakdown of cell membrane. The experimental data shows that when the electromagnetic field radiation time is less than 1 μ s. When the membrane potential is lower than 1V, this breakdown is reversible. However, if it is exposed to electromagnetic radiation for a long time, it will form irreversible breakdown. Some scholars took pictures of the broken cell membrane of brewer's yeast magnified by an electron microscope, which showed that the conventional heating caused the cell membrane to break into chaotic fragments, while the edge interface of the broken cell membrane wall under microwave radiation was neat, and there was a significant difference in the condition of the broken cell membrane between the two. German scholars also pointed out experimentally that when the instantaneous microwave electric field intensity reaches 2-20kv/m, the bacterial cell membrane can be broken, and the temperature of the material will not rise significantly.
For the cells of microorganisms, the cell wall that makes up the cell is to protect the overall survival interface of the cell. If the cell wall is damaged (for whatever reason, including electromagnetic damage) and breaks, the nucleic acid, protein and other body fluids in the cell leak out of the body, which is fatal to microorganisms.
In a word, both the response theory and the polarization breakdown theory reflect the physiological activities of cells, and the abnormalities under the external microwave electromagnetic field environment are the effects of electrical properties, resulting from the unique physical environment of microwave sterilization. It shows that the microwave sterilization method changes the single physical environment of conventional heating into a dual physical environment, that is, the physical environment with thermal and electromagnetic properties, and the electromagnetic force plays a leading role in strengthening the sterilization, which is the fundamental reason why microwave sterilization is superior to conventional heating sterilization.
3. Technological characteristics of microwave sterilization
And microwave heating As for drying, microwave energy penetrates into materials, so microwave sterilization is also applied to materials as a whole. Compared with conventional heating sterilization, microwave sterilization has the following simultaneity:
⑴ The simultaneity of sterilization of all parts of the material means that it can simultaneously sterilize the surface of the material or other parts of the material (including the inside of the material). The simultaneity of the sterilization parts is very conducive to sterilization and preservation of thick materials such as bread and moon cakes in food. Taking bread as an example, the temperature of conventional baking bread itself does not rise too high, about 60-70 ℃, and its central sterilization temperature is low, and the central sterilization temperature can not be maintained for a long time, which often makes the internal sterilization of bread incomplete. Therefore, the mildew of bread begins again. The freshness of domestic baked bread can only last for two or three days. If it is sliced bread - shaped bread is processed into slices, its fresh-keeping period is shorter, because the bread will be secondary polluted by the knife and the mold scattered in the air during the slicing process. For this reason, Swiss Carroll Company uses a microwave sterilization device for bread to sterilize sliced bread. Its power is 80kw, and its working frequency is 2450MHz. After microwave irradiation for a few minutes, the temperature of bread slices rises from room temperature to 80 ℃, and heat preservation treatment is conducted for 5-6min.
Domestic examples of microwave sterilization and fresh-keeping, such as Zolai filling noodles, moon cakes, sandwiches (pies), have also been successful.
The simultaneity of sterilization of each part of the material provides favorable conditions for shortening the total sterilization time and improving the sterilization quality, which can avoid the impact of long-term heating sterilization on food quality. Especially for foods that should not be sterilized at higher temperature or for longer heating time, such as ginger powder with volatile spice ingredients, fresh and tender jellyfish with more water, etc. For materials that need to be sterilized while maintaining the quality requirements such as color, flavor and taste unchanged, microwave sterilization can achieve good results.
⑵ Simultaneous sterilization time. It can ensure that the sterilization process conditions of materials are consistent without lag.
4. Quantitative discrimination of bacterial death
It must be pointed out that in the process of sterilization, bacterial death has an integral effect. As we all know, the premise of temperature rise of each part of the material by relying on surface heat conduction determines that the temperature rise of each part of the material has a certain time interval during conventional heating, and the length of this time interval varies with the speed of its temperature rise rate. Therefore, the ambient temperature of bacteria death in the process of conventional heating sterilization is not a single temperature value, but includes the temperature experienced during the whole heating sterilization period from the thermal sterilization temperature of live bacteria death. The lethal rate (slope value) of living bacteria at each specific temperature is unequal. Therefore, during the whole heating sterilization period, we can not distinguish and determine the specific temperature and time at which the living bacteria died. The lethal value of bacteria detected in the experiment can only represent the cumulative value of the number of bacteria killed during the heating period. If expressed in mathematical language, this value is only the integral effect of bacterial death on temperature and time. In this sense, it also shows that the lethal integral effect of the bacterium is related to its path (selection of temperature and time), and has certain complexity. Obviously, the microwave heating material is the overall heat source, and the complexity of this integral effect is greatly reduced.
The concept of food sterilization is different from that of medical sterilization. Food sterilization only refers to the sterilization required by commercial requirements, which means that it is required to kill the putrefactive bacteria, pathogenic bacteria and mold bacteria that can reproduce during normal storage and sales and cause food deterioration and corruption, so as to ensure the health of consumers, which is different from the sterility required by medical requirements. It must be pointed out that microwave sterilization can completely meet the aseptic requirements of food and other logistics after microwave sterilization in technology, but people still change or do not change the flavor and quality requirements of food after commercial sterilization and medical sterilization when using microwave sterilization. Therefore, its process feature is to give consideration to both sterilization and quality maintenance, As long as the commercial sterilization requirements can be met, it is enough. However, if the microwave sterilization process designed according to the requirements of medical sterilization, it must be determined with the ultimate goal of killing all bacteria
3、 Design of Industrial Microwave Sterilization Equipment
According to the needs of customers, different Microwave equipment 。 Please call for consultation.
