Application of microwave in the field of agricultural product processing

I. Overview With the continuous improvement of people's living standards and changes in consumer attitudes, higher and higher requirements are placed on the product structure, quality, safety and hygiene of the food industry, especially for various traditional and convenient bagged foods. It has become a hot spot for consumption in today's food market. However, in the production, storage, transportation and sale of these foods, it is highly susceptible to deterioration and loss of commercial value. Although the National Food Sanitation Law has strict regulations on the health indicators of various foods, in general, it is difficult to meet the standards. This not only greatly affects the shelf life of goods, but also is extremely detrimental to the health of the people. Although conventional techniques such as high temperature drying, blanching, pasteurization, freezing, and preservatives can generally be used to achieve insecticidal sterilization and preservation of food. However, these devices are large in size, long in processing time, incompletely sterilized or difficult to achieve automated production, and often affect the original flavor and nutrients of the food. Microwave insecticidal sterilization is to make microorganisms such as insects in food, and at the same time, it is combined with the microwave thermal effect and the non-thermal effect to cause the protein and physiological active substances in the body to mutate, which leads to the growth and development of the microorganisms, delaying and dying. The purpose of insecticide, sterilization and preservation.
Second, the mechanism of microwave sterilization and preservation Microwave sterilization, preservation is the hope that the food can be treated by microwave energy to make the bacteria, bacteria and other microorganisms in the food lose vitality or death, to ensure that the food contains no more than the food in a certain storage period The scope of the stipulations provided by the Health Law, thereby extending its shelf life.

The following is a brief description of the possible mechanism of microwave sterilization: it is well known that bacteria and adults, like any biological cell, are a coagulation medium composed of complex compounds such as water, protein, carbohydrates, fats and inorganic substances. Among them, water is the main component of biological cells, and its content is 75-85%. Because all kinds of physiological activities of bacteria must be carried out by water, the growth and reproduction process of bacteria and the absorption of various nutrients are through cell membrane. Diffusion, osmotic absorption to complete. Under the action of a certain intensity microwave field, the insects and bacteria in the food will also relax due to molecular polarization, while absorbing microwave energy to heat up. Because they are condensed matter media, the strong interaction between molecules increases the energy conversion of microwave energy to thermal energy. Therefore, the protein in the body is simultaneously subjected to both non-polar thermal motion and polar rotation, and the spatial structure is changed or destroyed to denature the protein. After denaturation of the protein, its solubility, viscosity, swelling, permeability, and stability all change significantly, and the biological activity is lost. On the other hand, the non-thermal effect of microwave energy plays a special role in conventional physical sterilization in sterilization, and is also one of the reasons for the death of bacteria. Microwave sterilization and preservation are the result of the combined effects of microwave thermal and non-thermal effects. The thermal effect of microwaves mainly plays a role in rapid temperature sterilization; while the non-thermal effect uses the proteins and physiologically active substances in microorganisms to mutate and lose vitality or death. Therefore, the microwave sterilization temperature is lower than the conventional method. Generally, the sterilization temperature of the conventional method is 120 ° C - 130 ° C, the time is about 1 hour, and the microwave sterilization temperature is only 70 ° C - 105 ° C, and the time is about 90-180 seconds.

Third, the characteristics of microwave sterilization and preservation 1, short time, fast speed Conventional thermal sterilization is through heat conduction, convection or radiation to transfer heat from the food surface to the interior. It takes a long time to reach the sterilization temperature. Microwave sterilization is a direct interaction between microwave energy and microorganisms such as food and bacteria. The thermal effect and non-thermal effect work together to achieve rapid heating and sterilization, and the treatment time is greatly shortened. The sterilization effect of various materials is generally 3-5 minutes.
2, low temperature sterilization to maintain nutrients and traditional flavor Microwave sterilization is through special thermal and non-thermal effect sterilization, compared with conventional thermal sterilization, can achieve the desired disinfection effect at a lower temperature and a shorter time. Practice has shown that the general sterilization temperature can achieve the effect at 75-80 ° C. In addition, the microwave treatment food can retain more nutrients and color, fragrance, taste, shape and other flavors, and has a puffing effect. For example, conventionally heat treated vegetables retain 46-50% of vitamin C, while microwave treatment is 60-90%. Conventional heated pig liver vitamin A is maintained at 58%, while microwave heating is 84%.
3, energy conservation Conventional thermal sterilization often has heat loss in the environment and equipment, and microwaves directly deal with food, so there is no additional heat loss. In addition, its conversion efficiency of electric energy to microwave energy is 70-80%, compared with 30-50% of electricity.
4. Uniform and thorough Conventional thermal sterilization starts from the surface of the material and is then transmitted to the inside through heat conduction. There is an internal and external temperature difference. In order to maintain the flavor of the food and shorten the processing time, the inside of the food does not reach a sufficient temperature to affect the sterilization effect. Since the microwave has a penetrating effect, when the food is processed as a whole, both the surface and the inside are simultaneously acted upon, so the sterilization is uniform and thorough.
5, easy to control microwave food sterilization treatment, the equipment can be used immediately, without the thermal inertia of conventional thermal sterilization, flexible and convenient operation, microwave power can be continuously adjusted from zero to rated power, transmission speed is continuously adjusted from zero, easy to control .
6. Simple equipment and advanced technology Compared with conventional disinfection and sterilization, microwave sterilization equipment does not require boilers, complicated pipeline systems, coal yards and transportation vehicles, as long as it has basic conditions of water and electricity.
7. Improve working conditions and save floor space The working environment temperature of the equipment is low and the noise is small, which greatly improves the working conditions. The entire microwave equipment operator only needs 2-3 people. Widely used in fungus, ginseng, flowers, onion ginger and garlic slices. The heating, drying and sterilization of jujube tablets, peppers, dehydrated vegetables, soy products, etc., through microwave sterilization and preservation technology, will not damage the original nutrients of the materials, the health indicators can be completely lower than the national food hygiene standards, completely It can reach the export-grade standard of food and greatly extend the shelf life of food.