Research on the cold sterilization technology of t

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Research on food cold sterilization technology (II)

2 radiation sterilization

radiation (or irradiation) sterilization is the use of ionizing rays with extremely short wavelength that can certainly meet the experimental measurement needs of different materials to sterilize food. Rays commonly used in food sterilization are χ- Ray γ- Rays and electron rays. Electron rays are mainly obtained from electron accelerators, χ- Ray by χ- Ray generator generation, γ- X-rays are mainly obtained from radioisotopes, commonly used radioisotopes are 60Co and 137Cs. γ- The penetration of rays is very strong, which is suitable for the internal sterilization of complete food and various packaged food. The penetration of electronic rays is weak, which is generally used for the sterilization of small packaged food or frozen food, especially for the surface sterilization of food. 2.1 mechanism of radiation sterilization. The effect of radiation on food is divided into primary and secondary. The primary is the ionization and chemical action of microbial intercellular substance after being irradiated by high-energy electron rays, and the secondary is that water produces various free radicals and hydrogen peroxide after radiation and ionization, and then interacts with other substances in the cell. These two effects will hinder all activities in microbial cells, resulting in microbial cell death

the purpose of food radiation sterilization is different, and the radiation dose used is also different. The radiation dose of complete sterilization is 25~50kgy. Its purpose is to kill all microorganisms except bacillus, which are integrated with downstream systems (such as handling robots and molding presses). The radiation dose of disinfection and sterilization is 1~10kgy. Its purpose is to kill the pathogen that does not produce spores in food, reduce microbial pollution, and extend the storage period. In short, for different microorganisms, different radiation doses and electronic energy need to be controlled

2.2 the effect of radiation on the nutritional composition of food after the normal recommended dose of radiation, the nutritional components of food, such as protein, sugar, trace elements and minerals, have little loss, but vitamins and fats are sensitive to radiation. The degree of vitamin loss after radiation is related to the type of food, radiation dose, temperature, oxygen content and the type of vitamins. Generally speaking, fat soluble pheromone is more sensitive to radiation than water-soluble vitamin. Comparing the destructive effect of water-soluble vitamins in irradiated and heated foods with bactericidal dose, it can be found that there is almost no difference between them, while the fat soluble vitamins lose more, especially vitamin E and K. Among the water-soluble vitamins, the loss of vitamin C is the largest and the loss of niacin is the smallest. After high-dose radiation, the free radicals and their derivatives produced by oxidation reaction will promote the oxidation of fat and make it rancid, resulting in the reduction of the digestion and absorption rate of fat

2.3 effect of irradiation on color, flavor and texture of food

2.3.1 color irradiation has different effects on various food pigments. Plant pigments are relatively stable to irradiation treatment. Animal ima plans to provide guidance to specifiers, architects and construction personnel through a series of UK industry roundtables in 2018. Physical pigments are sensitive to irradiation. Irradiated hydrolysates can lead to oxidation of myoglobin and fat, causing discoloration. Irradiation can deepen the stable red or pink of frozen poultry breast meat. The deepening of red depends on the type of meat, intramuscular type, radiation dose and packaging materials. According to the report of NHM et al., the reducibility of irradiated meat increases, producing CO, which is strongly compatible with blood red pigment and improves the strength of red or pink. According to relevant research reports, using less than 1% Co combined with modified atmosphere packaging can maintain the stable strawberry red color of meat for 8 weeks, and prolong its shelf life. Kusmide further studied that adding less than 1% CO during packaging can greatly improve the color and flavor of fresh minced beef. At the dose of 4.5kgy, CO can reduce fat oxidation and provide a stable strawberry red color. In other words, CO packaging combined with low or medium dose irradiation can bring a pleasant and safe color to fresh beef offal with minimal quality damage

2.10 samples can only be successful for 1 and a half. 3.2 odor irradiation treatment will generally cause the loss of the unique aroma of food, and also produce unpleasant "radiation odor", especially meat food. Pratl reported that raw ham treated with 24kgy radiation had odor. Nam et al. Compared the irradiation effect of aerobic packaging and vacuum packaging of Turkey chicken breast meat. The experiment pointed out that the volatile odor will be produced during irradiation, accompanied by the oxidation of fat and the generation of volatile sulfur. The formation of volatile substances in aerobic packaging will increase with the increase of radiation dose and the extension of storage time. Ahn et al. Pointed out that sulfur compounds are the root cause of the peculiar smell of irradiated frozen pork. The irradiation hydrolysate of protein plays an important role in the generation of peculiar smell of irradiated meat

2.3.3 texture low dose radiation treatment of food will not have a significant impact on the texture of food. On the contrary, it can also inhibit softening, destroy the activities of some enzymes that cause post ripening of fruits, and delay the post ripening of some fruits. When food is treated with high dose irradiation, there will be softening in varying degrees, which is caused by the depolymerization of food macromolecules. Setsuko et al. Pointed out that the surface of dry materials irradiated by electrons with 300kV or lower can remove pollution (such as beans, spices, dehydrated vegetables and tea), which will not produce harmful effects. Treating soybeans with 170KV voltage can reduce the number of microorganisms to an undetectable level. The gelling property of soybean milk treated by soft electron is better than that of high-pressure sterilization. The quality of soybean milk and tofu processed by soft electron sterilization can be improved. McKenna et al. Pointed out that irradiation can increase the sensory tenderness and juice score of salmon, and increase the flavor intensity of catfish fillets

2.3.4 application of radiation sterilization in food industry aquatic products, meat products, eggs and bee pollen can be preserved for a long time after irradiation. After pretreatment, meat products are vacuum sealed, packaged and frozen, and irradiated at - 40 ℃, which has no adverse effect on meat products. Beef, chicken, ham, sausage, fish and shrimp that have been completely sterilized by radiation can be stored for a long time at room temperature, and longer if they are treated under low or no oxygen conditions. Generally, the irradiation sterilization of eggs can kill Salmonella with a dose of about 10kGy. If fresh eggs are irradiated with 80kgy electron rays, coated with a thin layer of polyvinyl alcohol plastic, and stored at 28 ℃ ~30 ℃ for more than a month, the good egg rate can reach 91.0% - 91.3%. Egg liquid and frozen egg liquid can be used β- and γ- Radiation, sterilization effect is good. Irradiation of bee pollen with a dose of 1.0kgy can effectively kill microorganisms in the pollen, and the temperature rise of the pollen is not obvious, which is very good for preserving the nutritional components of the pollen. In addition, radiation is also widely used for surface sterilization of packaging materials and packaging containers, and the general dose of 20~30kgy can meet the sterilization requirements. High voltage electron beam is suitable for sterilization of single-layer films

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