(1), high temperature and high pressure (pressure steam sterilization method);
② Gas fumigation (ethylene oxide) method;
(3) Sterilization by ionizing radiation (gamma rays and electron beams).
High temperature and high pressure method is the earliest sterilization method, and its main disadvantages are: incomplete sterilization; Not suitable for those heat-sensitive materials (such as plastic products, some rubber products, etc. ); This method also consumes a lot of energy; Can't work continuously, can't mass production. This is a primitive and backward method.
Gas fumigation is to fumigate sterilized articles with chemical substances, and the main chemicals used are ethylene oxide, methyl bromide and so on. Compared with the former method, it has made great progress: it can be produced in large quantities and sterilized thoroughly. However, this method has many disadvantages: many process parameters and difficult control; Can't produce continuously; Packaging materials must be breathable (but impermeable to bacteria); There will be microbial residues where the sterilized products are compressed and can not penetrate gas; There are chemical residues in the product. It is particularly worth pointing out that these chemicals are strong carcinogens. Although there are clear restrictions on residues, there are still residues that pose a threat to human health.
After the first two methods, people have adopted advanced radiation sterilization methods, and the radiation sources used are mainly gamma rays generated by radioisotope cobalt -60 and high-energy electron beams or X-rays generated by accelerators. This method is an environment-friendly sterilization method: the sterilization process is easy to control (only the irradiation dose is controlled); Thorough sterilization, no heat convection and gas diffusion problems; Because it is carried out at room temperature, this method is practical for all kinds of heat-sensitive materials. Can be continuously produced on a large scale; The product does not produce induced radioactivity and has no pollution.
"Since 199 1, Europe and its trading partners have banned the use of ethylene oxide and methyl bromide for fumigation and disinfection in the medical and health industry. According to the Montreal Protocol on environmental protection promulgated by 1989, it is necessary to stop using chemicals that destroy the ozone layer, such as ethylene dibromide, methyl bromide or ethylene oxide, for food fumigation and sterilization. Instead, it is a pollution-free gamma-ray irradiation sterilization method such as cobalt -60. " (Excerpted from Science Times).
From the above comparison, it is not difficult to see that irradiation sterilization is the most advanced sterilization method at present, and most medical and health products in developed countries are sterilized by this method. As we all know, irradiation sterilization is used to replace other sterilization methods, and it is an irreversible trend to eliminate ethylene oxide gas fumigation sterilization.
In fact, irradiated foods are gradually entering the homes of ordinary people, such as dehydrated vegetables, instant noodle seasonings and vacuum-packed cooked meat products, health drinks and local products. From June 1998 to June 1, all irradiated foods sold in China market must be labeled with irradiated foods, which are gradually recognized and accepted by consumers.
Irradiated food uses 60Co γ-rays, X-rays or high-energy electron beams to penetrate the food body, ionize water and various nutrients, and then destroy DNA molecules in cells (the destruction of cytoplasm and biofilm is also an important process), thus inhibiting the germination and rooting of vegetables. The irradiated grain will not be moth-eaten and moldy within 3 years; The shelf life of garlic, potato and onion can be prolonged by 6 ~ 12 months after irradiation.
After radiation treatment, meat and poultry food can completely eliminate corrupt and pathogenic microorganisms such as mold and Escherichia coli, thus greatly prolonging its shelf life. Developing irradiated meat is beneficial to improve the competitiveness of China meat products in the international market. In recent years, the meat production in China has been increasing continuously. For example, 1995, China's livestock meat output reached 49.66 million tons, accounting for 20% of the world's total output, ranking first in the world. However, exports did not increase at the same time, and the export volume of major varieties even declined. One of the important reasons is that the hygienic standard of related meat products can not meet the import requirements of developed countries and regions in Europe and America. According to the Montreal Convention, the use of traditional refrigerant methyl bromide was completely banned in developed countries before 2005 and in developing countries 20 15 years ago. This poses a challenge to the traditional method of preserving meat in China, but it provides an opportunity for the development of irradiated meat market. For example, the shelf life of small packaged fresh meat products circulating in major supermarkets is generally 2 days at 2 ~ 4℃, and even if vacuum packaging or vacuum inflatable packaging is adopted, the shelf life is only 5 ~ 7 days. However, if vacuum packaging or vacuum inflatable packaging is used and low-dose irradiation is used, the shelf life of irradiated fresh meat is 30 days at 2 ~ 4℃, which has effectively killed various parasites and pathogens and greatly improved. Radiation chemical products are the fastest developing field of radiation processing technology. Radiation chemistry is a new processing method to modify materials through chemical changes (combination, decomposition, crosslinking, polymerization, grafting, curing, degradation, etc.). ) is caused by ionizing radiation. Compared with conventional processing technology (heat treatment, optical processing, chemical processing, etc.), its main feature is that it can react at room temperature to low temperature without adding initiator or catalyst, and can synthesize or prepare high-performance special materials that are difficult to obtain by conventional methods.
Radiation chemical products have high added value and are widely used, involving many important fields of national economy such as communication electronics, electric power transportation, petrochemical industry, aerospace and so on, and occupy a very important position in radiation technology in the same industry. In recent ten years, with the upgrading of industrial structure and the enhancement of environmental awareness around the world, radiation chemical industry, as a green chemical industry with high efficiency, energy saving, no pollution and easy control, has attracted worldwide attention and shown strong vitality. Because of its simple process, convenient operation, good product quality and good benefit, its industrialization speed is very fast. Radiation chemical industry mainly produces chemical products by γ -ray irradiation to initiate heterogeneous polymer polymerization. Table 4 lists its application in detail. In this field, many products have been produced on a large scale, such as heat shrinkable materials, which have been applied to power and various departments. ① In agriculture, artificial mutation induced by radiation is called mutation breeding, that is, mutation is used to improve varieties. In other words, useful morphological traits can be directly used as varieties or as mating female parent materials. Its purpose is to increase yield and use varieties early. These aspects have made gratifying achievements.
② Sterilization of animal compound feed: A long time ago, more than 30 kinds of feed additives were designated as the objects of irradiation treatment. Irradiation processing technology has developed considerably in the treatment of aseptic feed, and its application prospect is very considerable. Experiments show that high-dose irradiation of protein and amino acids hardly causes nutritional changes, and there is no problem in the radiation decomposition of vitamins except vitamins A and E. The decomposition degree of vitamins A and E is similar to that of heat treatment, especially most experimental feeds are irradiated. Leading enterprises in the domestic feed industry, such as Hunan Quyuan Zheng Hong Science and Technology Group and Zheng Da Group, can consider introducing this technology and project and applying it to the fields of feed production and meat product preservation.
(3) Radiation-treated starch: Radiation-treated starch has been widely valued, and it has been used as an auxiliary material for refined aquatic products and as a filler for baby food, patient food and dried gravy. In a word, the purpose of radiation treatment of starch is to modify industrial raw materials, sterilize food raw materials and improve processing adaptability.
(4) Radiation treatment of immobilized enzyme: enzyme is a protein with catalytic effect on biological objects. It can only be used once because it is soluble in water. After the reaction, the activity of the enzyme still exists, but it is unrecoverable for the enzyme. After heating, solidification and precipitation, it can only be taken out and thrown away. From the point of view of saving resources, it is uneconomical to use enzymes like this. If the enzyme can be solidified and participate in the comprehensive reaction, the enzyme reaction can be automated and continuous, and this complex can be produced under 60Coγ -ray irradiation. For example, in Kawayama Island, Japan, in 1975, the mixed solution of acrylamide and enzyme was frozen on dry ice acetone, and irradiated with 60Coγ gamma rays for 5- 10 minutes per hour to combine them. After thawing, it can be made into sponge-like membrane structure or beads-like immobilized enzyme.
⑤ Disinfection, sterilization and antisepsis of leather: It has special effects on freshly peeled leather. For example, freshly peeled cowhide. Sheepskin can be treated by radiation, so that it will not deteriorate and taste, and it will not rot for a long time.
6. Pasture: There are many microorganisms and germs in the pasture eaten by cattle and sheep. In order to ensure the healthy reproduction of cattle and sheep, the pasture after radiation treatment has been fed. In particular, these grasses have to be irradiated when they are exported.
⑦ It also has many applications in other fields, such as commodity conservation and flower preservation.
As can be seen from the above, irradiation technology has a wide range of applications. Facts have proved that radiation processing technology is a high-tech that is moving towards industrialization and commercialization, and it also shows that radiation processing technology is a very vital cause.