Higher than 100 degrees Celsius and lower than -20 degrees Celsius.
Bacteria also have a significant impact on human activity. On the one hand, bacteria are the causative agents of many diseases, including tuberculosis, gonorrhea, anthrax, syphilis, bubonic plague, and trachoma.
However, humans have also utilized bacteria from time to time, for example, in the making of cheese and yogurt and wine, the manufacture of some antibiotics, and the treatment of wastewater, all of which are related to bacteria. In the field of biotechnology, bacteria are also widely used.
Bacteria were first discovered by the Dutchman Levenhuk on the tartar of an old man who had never brushed his teeth, but at that time people thought that bacteria were naturally occurring. It was not until later that Pasteur pointed out with the gooseneck bottle experiment that bacteria were produced by existing bacteria in the air, rather than by themselves, and invented the "pasteurization method", which was later regarded as "the father of microbiology".
Extended information:
New heat sterilization technology
Ideal heat sterilization effect should be, in the heat of the food quality of the degree of influence on the minimum conditions, rapid and effective killing of harmful microorganisms in the food materials, to achieve the requirements of the product indicators. Ultra-high temperature sterilization, microwave sterilization and ohmic sterilization are new ways to achieve this ideal effect.
1) ultra-high-temperature sterilization
Ultra-high-temperature sterilization refers to the heating temperature of 135~150 ℃, the heating time of 2~8s, the heating of the product to achieve commercial sterility requirements of the sterilization process. This sterilization conditions relative to the conventional sterilization of low-acid food 100 ~ 135 ℃ used in 20 ~ 40 ℃ higher, so it is called ultra-high-temperature sterilization.
Application:
A large number of experiments show that the sensitivity of microorganisms to high temperatures is much greater than the sensitivity of most food ingredients to high temperatures, so UHT can effectively kill microorganisms in a very short period of time, and better maintain the quality of the food should be, and greatly extend the shelf life of the food. Therefore, it is now widely used in dairy, beverage and fermentation industries.
To achieve the sterilization requirements, while the food is not subject to thermal damage, the key to its technology is rapid heating and rapid cooling, the most commonly used heat transfer equipment is the plate heat exchanger. According to the material and heating medium direct contact or not, UHT process can be divided into indirect heating method and direct mixed heating method.
After UHT, the food reaches the commercial sterilization requirements, and must be aseptically packaged to prevent microbial contamination in the subsequent packaging, transportation, and marketing processes. However, the usual UHT equipment is only applicable to materials that do not contain particles or contain particles with a particle size of less than 1cm material heat sterilization. For granularity greater than 1cm of material, currently available microwave sterilization and ohm sterilization to achieve.
2) microwave sterilization
Microwave refers to the frequency of 300MHz ~ 300GHz, that is, the wavelength of 1m ~ 1mm of ultra-high frequency electromagnetic waves. Microwave sterilization is the result of thermal and non-thermal effects of **** the same.
On the one hand, the microwave penetrates the medium, polar molecules by the alternating electric field and orientation movement, friction and heat, resulting in thermal effects; on the other hand, organisms and microwave action will produce complex biological effects, that is, the non-thermal effect, such as microwave electric field to change the cell membrane cross-section of the distribution of electrons, so that the permeability changes; caused by the protein denaturation;
Changing the physiological and biochemical reactions of the activation energy; induces various ionic groups, so that the physiological active substances of microorganisms change; lead to the relaxation, breakage and recombination of hydrogen bonds in the structure of DNA and RNA, inducing some gene mutations and interrupting the normal physiological functions of cells.
Application:
Microwave heating equipment is mainly composed of DC power supply, magnetron, heater, controller and cooling system, which can be applied to a series of products such as meat products, poultry products, aquatic products, fruits and vegetables, canned food, dairy products, crops, pudding and bread.
3) Ohm sterilization
Ohm sterilization is the use of electrodes, the current is directed into the food, by the food itself dielectric properties of the heat generated by the purpose of direct sterilization.
Application:
Ohm sterilization technology is suitable for the treatment of liquid materials with high viscosity, and can contain some particles of materials, such as broth, pudding commercial aseptic treatment. The use of ohmic heating, so that the heating rate of the particles and the liquid heating rate close to the heating rate of the possibility, and can be obtained than the conventional method of particle heating rate (1 ~ 2 ℃ / s), and therefore can shorten the processing time, to obtain high-quality products.
Ohm sterilizing device system mainly consists of pump, column-type ohm heater, heat preservation tube, control instrumentation and so on, of which the most important part is column-type ohm heater. When heating high-acid products, the counterpressure is maintained at 0.2MPa and the sterilization temperature reaches 90~95℃, and when heating low-acid foods, the counterpressure is maintained at 0.4MPa and the sterilization temperature reaches 120~140℃.
At present, the British APVBaker company has manufactured industrial-scale ohmic heating equipment, which can make high-temperature transient technology applied to the processing of food containing particles (particle size up to 25mm).
Baidu Encyclopedia - Bacteria