Materials suitable for irradiation

Different types of microorganisms have different sensitivity to radiation. This inherent sensitivity is called "resistance". From the perspective of cell metabolic activity, the radiosensitivity of cells and tissues is proportional to their reproductive capacity and inversely proportional to the degree of differentiation. In the early stage of cell division, which is the period of DNA replication, it is the most sensitive to radiation. The rate of cell metabolism is one of the important factors that determine the radiosensitivity of cells. Therefore, any physical and chemical factors that affect metabolism will affect the radiosensitivity of cells. In addition, different kinds of microorganisms have different sensitivity to radiation. A large number of recent experimental results show that Bacillus pumilus, Bacillus subtilis and their variants have the same strength. The resistance of lipobacillus thermophilus, Bacillus megaterium and perforator Clostridium botulinum were more obvious than that of Bacillus pumilus.

 

medium

Suspension or attachment of microorganisms to different media has a great influence on the sensitivity of irradiation. Dried serum Roufen can protect bacteria against radiation damage, and fatty film, agarose and other compounds also have this effect. This protective effect is shown by delaying the mortality curve.

 

oxygen

Oxygen can increase the sensitivity of pseudobacteria to radiation. If anoxic conditions are maintained during and after irradiation, the tolerance of microorganisms is often increased by 2-5 times. For example, the D2 value of Bacillus brevis spores exposed to radiation in the air was 175 kGy (0.17 mrad), and in hypoxia was 3.6 kGy (0.306 mrad). However, a small amount of oxygen is sufficient to maintain maximum sensitivity. Potassium permanganate is a strong oxidant and can replace molecular oxygen. It makes spores sensitive to radiation under anaerobic conditions, but does not increase when oxygen is used.

 

temperature

The radiosensitivity of biological system decreases with the decrease of irradiation temperature. When the spores of Clostridium spp. (strain 33a) were irradiated in phosphate buffer and soybean broth, the tolerance of Clostridium spp. This may be due to the weakening of the activity of free radicals produced by irradiation at low temperature, thus reducing their interaction with oxygen and reducing the damage caused by oxygen effect. Other studies have shown that increasing temperature by 10 ℃ can reduce D10 value by 50%. Therefore, it is very useful to combine radiation with moist heat or dry heat sterilization in food industry. Under certain conditions, synergism can be observed when heating and radiation are simultaneously provided.

 

Chemical factors

Glycerol, thiourea, dimethyl sulfoxide, sulfhydryl compounds, vitamin C, protein and so on may protect bacteria against radiation damage by scavenging free radicals. The other is chemical sensitizers, such as aminophenol, sulfoacetamide, n-acetylmaleimide, naphthalene, halide, nitrate, nitrite, vitamin K, etc., which can increase the sensitivity of microorganisms to radiation.

 

Ionizing radiation has been used for sterilization for many years. The earliest report of irradiation sterilization for preservation of food was found in the 1930 US patent collection. Since the first use of electron beam to sterilize surgical sutures in the United States in 1956, irradiation sterilization technology has been rapidly commercialized and commercialized. In the 1950s, China built large-scale co gamma ray irradiation sources for commercial irradiation. The application field of this radiation sterilization technology expanded rapidly, from the initial sterilization of disposable medical supplies to the sterilization of medical equipment materials, medical drugs, food sterilization and preservation, disposable household goods sterilization, environmental microbial pollution control and so on.