The principle of microwave sterilization
The microwave sterilization equipment utilizes the interaction of microwave thermal effect and biological effect. The potential distribution of microwave on the cross section of bacterial membrane affects the concentration of electrons and ions around the cell membrane, thus changing the permeability of the cell membrane. As a result, bacteria are malnourished, unable to metabolize normally, and their growth and development are hindered and die.
From the biochemical point of view, nucleic acid (RNA) and deoxyribonucleic acid (DNA) that bacteria normally grow and reproduce are curled macromolecules that are closely connected by several hydrogen bonds. Microwave causes hydrogen bonds to relax, break and recombine, thus inducing genetic genes or chromosomes to be distorted or even broken. Microwave sterilization uses electromagnetic field effect and biological effect to kill microorganisms. Practice has proved that microwave devices have obvious advantages in sterilization temperature, sterilization time, product quality maintenance, product shelf life and energy saving.
Characteristics of microwave sterilization
1. Short time and high speed
Conventional thermal drying sterilization transfers heat from the surface of an object to the inside by means of heat conduction, convection or radiation. It often takes a long time to reach the required dryness and sterilization temperature inside the object. The medium consists of polar molecules and nonpolar molecules. Under the action of electromagnetic field, these polar molecules change from the original random distribution to the orientation according to the polarity of electric field. However, under the action of high-frequency electromagnetic field, these orientations change constantly according to the frequency of alternating electromagnetic field, which causes the movement and friction of molecules and thus produces heat. At this time, the field energy of alternating electric field is transformed into heat energy in the medium, which makes the temperature of the medium rise continuously, so microwave heating is the loss of electric field energy and heat generation of the medium material itself. Therefore, the processing time of microwave heating is greatly shortened, and under a certain power density, it usually takes only tens of seconds and minutes to achieve satisfactory results.
2. Low-temperature drying and sterilization can keep the nutrients
Microwave has the dual sterilization functions of rapid heating with thermal effect and non-thermal effect, and can obtain the required drying and sterilization effect at a lower temperature and in a shorter time compared with conventional thermal drying and sterilization. Generally, the sterilization temperature is 65-7℃, 75-8℃ or 13-121℃, and the time is 3-8 minutes, and more food nutrients and flavors such as color, aroma, taste and shape can be retained. For example, the vitamin C in vegetables treated by conventional heating is 46-5%, compared with 6-9% by microwave treatment, 58% by conventional heating and 84% by microwave heating.
3. Save energy
Microwave power conversion efficiency is high, generally above 7%. Microwave directly treats food, and the heating box itself is not heated, so there is no extra heat loss, so it saves energy and electricity, generally 3-5%.
4. Uniformity and thoroughness
Conventional thermal drying and sterilization start from the surface of the material and then spread to the inside of the material through heat conduction. There is a temperature difference between the internal and external temperatures of materials, and the consistency of drying and sterilization effects inside and outside is poor. In order to keep the flavor and shorten the treatment time, the internal temperature often does not reach enough, which affects the drying and sterilization effect. This phenomenon can be improved by increasing the treatment temperature, however, it reduces the quality of the surface of the article, such as color, fragrance, taste and shape. Microwave has penetrating performance, and the surface and the interior act at the same time, which can ensure that the internal and external temperatures reach the required value together, so the drying and sterilization are uniform and thorough.
5. It is easy to control and realize automatic production.
The microwave food drying and sterilization equipment is simple to operate, easy to control, and has no thermal inertia. It can be processed according to the requirements of different food process specifications, reducing production operators and production costs.
6. Simple equipment and advanced technology
Compared with conventional sterilization, microwave equipment does not need boilers, pipeline systems, coal yards and transport vehicles, as long as it has the basic conditions of water and electricity, and has no special requirements for factory buildings, with less investment and quick results.
7. Improve working conditions and save floor space
Microwave equipment is free from high temperature, helpless heat, self-heating and thermal radiation. It can greatly improve the working conditions, and the equipment structure is compact, saving the workshop area.