With the development of science and technology, sterilization methods and methods are increasingly diversified, and are developing in the direction of safety, efficiency, energy conservation and environmental protection. The traditional sterilization method is heat sterilization. Because the heat transfer performance of food is generally poor, the time required for the material center of the food to reach the sterilization temperature is long, resulting in a decrease in the nutritional value of the food. In addition, energy absorption due to the heat capacity of the heating device itself causes energy absorption. High consumption, high temperature and easy to make food "cooking taste" and "canned taste", to a certain extent, limit consumers' choice of high temperature food.
In comparison, the microwave sterilization temperature only needs 65~85°C, and the sterilization time is 5-10 minutes. The whole process does not damage the nutrient content of the material, and is widely used in the sterilization of seasonings, vacuum-packed foods, sauces, etc. It can be used for sterilization of agricultural products and chemical products.
Microwave has the dual effect of thermal and non-thermal effects. Microwave thermal effect sterilization mechanism refers to: a biological cell is a condensed medium composed of complex compounds such as water, protein, nucleic acid, carbohydrate, fat and organic matter. The medium is heated by the action of a strong microwave field. The spatial structure changes or destroys, and the protein denatures, affecting its solubility, viscosity, swelling, stability, and thus losing biological activity.
Conventional thermal sterilization is to transfer heat from the surface of the food to the inside through heat conduction, convection or radiation. It often takes a long time for the internal temperature to reach the sterilization temperature. The microwave uses its transmissive action to combine the thermal effect and the non-thermal effect to uniformly and rapidly heat the bacteria inside and outside the article. The processing time is greatly shortened, and even under a strong power density intensity, even a few seconds to several tens of seconds can achieve satisfactory results.
Low temperature sterilization and maintenance of its nutrients The rapid heating of the microwave thermal effect and the biochemical action of the non-thermal effect enhance the bactericidal function. Microport has a processing method that retains more active ingredients. Maintain the original color, fragrance, taste, shape and other flavors. For example, the conventional treatment of vegetables with vitamin C is 46-50%, microwave treatment can reach 60-90%; conventional heating pig liver vitamin A is maintained at 58%, while microwave heating is 84%.
Microwave thermal efficiency is high, generally above 80%, far superior to other heating methods. In addition, the microwave directly converts the magneto-thermal energy to the food (object), and the microwave heater itself is not heated, so there is no additional thermal power consumption, so energy saving, compared with energy saving 30-50%.
Conventional thermal sterilization starts from the surface of the material. Through heat conduction, it gradually heats up from the inside and outside. There is a temperature difference gradient inside and outside, which causes the internal and external sterilization effects to be inconsistent. The thicker the problem, the more prominent the problem. In order to maintain the flavor of the food and shorten the processing time, it is necessary to increase the treatment temperature to shorten the processing time, but this will reduce the color, fragrance, taste, shape and the like of the food surface. The penetration of the microwave allows the surface and the interior to be heated at the same time to ensure uniform sterilization inside and outside.