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1. Microwave Sterilization Technology Microwave is a kind of high-frequency electromagnetic wave. When it acts in the medium, polar molecules such as water, protein, fat, and carbohydrate are violently oscillated by the action of the alternating electric field, causing strong friction. Heat, this is the dielectric induction heating effect of microwaves. This thermal effect also changes or inactivates the molecular structure of proteins, nucleic acids, etc. in microorganisms; the high-frequency electric field also changes the membrane potential and polar molecular structure; these all have a destructive effect on microorganisms and thus have a bactericidal effect. Using microwave sterilization, the processing time is short, and it is easy to realize continuous production without affecting the original flavor and nutrient components. Because of its good penetrability, it can be sterilized after packaging.
It has been reported that the use of 2450 MHz microwave processing soy sauce can inhibit the growth of mold and kill intestinal bacteria. Used for the sterilization of beer, achieving good results, and keeping the beer flavor well. It was used to treat cakes, moon cakes, sliced ​​bread and spring rolls. The results showed that the shelf life of these foods was extended from the original 3d-4d to 30d. Wu Hui reported that compared with the general heating and sterilization method, microwave sterilization has reduced the time of death of bacteria and fungi at a certain temperature. With Bacillus subtilis as the material, the D100 of microwave method is 0.65, and the control of Pap The law is 5.5. The lethal temperature of microwave sterilization under the same conditions is lower than that of conventional heat sterilization. In the 60s and 70s, foreign countries began to consider applying microwave technology to the actual production of fresh milk, beer, biscuits, bread, pigs, and beef. By the 1990s, process parameters and optimization have become hot topics for research.
2, high-pressure sterilization technology The so-called high-pressure sterilization refers to the release of food into the liquid medium, add 100MPa-1000MPa pressure for a period of time, like heating, kill the microorganisms in the food process. In autoclaving, proteins are usually considered to deform under high pressure (quadruplex structure) to denature and inactivate bacteria. However, some people think that biopolymers such as nucleic acids, polysaccharides, and fats that are composed of weaker bonds are generally considered. Other substances or cell membranes are affected by ultra-high pressure, especially through the shear force to rupture the biological membrane, so that the life activities of the organism are affected or even stopped, which can achieve sterilization, insecticidal and effect. Autoclaving avoids the various drawbacks that affect the quality of food that occur during heat treatment, maintaining the original flavor, color, and nutritional value of the food. Due to the instantaneous compression process of the liquid medium, sterilization is uniform, there is no pollution, operation is safe, and the energy consumption is lower than the heating method, and the environmental pollution is reduced. Li Jianrong et al studied the juice and vegetable juices after high pressure treatment. The experiment confirmed that high pressure treatment can achieve the bactericidal effect, and Vc loss is very little, the residual enzyme activity is only 4%, and the sensory indexes such as color and aroma are not changed. The effect is better than heat sterilization; animal food can also achieve bactericidal effect. At present, it has been used in foreign countries for the processing of meat, eggs, soy protein, fruits, spices, milk, fruit juice, mineral water, beer and other items. China's development and application of this technology is only in the laboratory research stage, and there are no reports of mass production.
3. High-voltage pulsed electric field sterilization technology The high-voltage pulse technology is used for food inactivation of enzyme sterilization. The main principle is based on the difference in electrical characteristics between the cell structure and the liquid food system. When a liquid food is placed in an electric field as a dielectric, the cell membrane of microorganisms in the food is electro-punctured under the action of a strong electric field, resulting in irreparable perforation or rupture, which damages the cell tissue and leads to inactivation of the microorganism. It was confirmed that the pulsed electric field intensity of 12-40 Kv/cm and the pulse time of 20 μs-18 μs can effectively sterilize the food, and the double rectangular wave is most effective. Deng Yuanxu et al. used pulsed high pressure to kill yeast and E. coli, obtained good experimental results, and had low energy consumption. The temperature rise of the test solution was less than 2°C, which could effectively preserve the nutrient composition and natural characteristics of the food. Treatment of soybeans with a pulsed electric field can achieve enzyme inactivation and effectively preserve the aroma of soybeans. This technology is a new non-thermal sterilization technology at room temperature. The use of this technology should consider the factors such as the strength of the field, the time of sterilization, the pH of the food, and the type of bacteria, in order to determine the best solution. At present, the technology is in the stage of research and development in the international arena. After further maturation, it is likely to make up for the inadequacies of traditional sterilization methods and bring about a revolution in liquid food technology.
4, pulse light sterilization technology pulse light sterilization is the use of strong white flash flash disinfection technology, the system includes power unit and lamp unit, power unit for the inert gas lamp to provide energy, the lamp will only last for hundreds of microseconds, Its wavelength is from the ultraviolet light region to the near infrared light region strong light pulse, its spectrum is similar to the sunlight, but is several thousand times to the tens of thousands times stronger than the sunlight. Due to the fact that only the food surface is treated and therefore the nutrient content of the food has little effect, studies by Joseph Dunn et al. have shown that pulsed intense light has a lethal effect on most microorganisms. Zhou Wanlong and other studies have shown that the energy input by the light pulse is 700 J, and the light pulse width is less than 800 μs. After flashing 30 times, it has a strong lethal effect on B. subtilis, E. coli, and yeast. The activity of amylase and protease in the solution also has obvious passivation. The pulse width is less than 800μs, its wavelength ranges from the ultraviolet region to the infrared region, the sterilizing wavelength band may be the ultraviolet region, and other wavelengths may have a synergistic effect; the pulse light sterilization has little effect on the conductivity of the bacterial suspension, causing The change of potential, its cause and its influence on the morphology and structure of microorganisms are yet to be further studied.
Commonly used sterilization method
Some basic concepts:
Sterility: No living microorganisms in objects or in certain media.
Sterilization: Physical or chemical methods are used to kill all the microorganisms on the object or in the medium and their spores are killed.
Disinfection: kill pathogenic microorganisms on or in objects by physical or chemical methods.
Preservation: The use of physical or chemical methods to inhibit the growth of microorganisms, also known as bacteriostasis.
First, the physical sterilization method:
(a) heat sterilization method:
1, dry heat sterilization: the use of fire or dry hot air sterilization, mostly for utensils and utensils.
2, hot and humid sterilization:
(1) Autoclave sterilization: After evacuation of air with saturated water vapor, sterilization is performed at a certain temperature and pressure. The steam pressure and temperature correspond to the following:
20.594(kpa)-105.7°C, 34.3233-108.8°C, 41.1879-110.3°C, 68.6466-115.5°C, 75.1121-116.8°C, 96.1052-120.2°C...
(2) Circulating steam sterilization method and boiled sterilization method: 100°C, suitable for agents that are not resistant to high temperatures.
(3) Low-temperature intermittent sterilization: heating at 80°C for 1 hour and 20°C to 25°C for 24 hours, and continuously operating for more than three times, suitable for heat-inhibiting agents. The sterilization effect is poor and preservatives must be added.
(B) filter sterilization method:
1. Melting glass filter: International standard is P250～P2, filtering particles are from big to small. P2 can filter out E. coli and Staphylococcus.
2, microporous membrane: China's cellulose acetate membrane filter, or nitrocellulose and cellulose acetate mixed cellulose ester membrane. Characteristics: Sterilized at 120°C for 30 minutes; No desquamation; Not resistant to alkalis; Not resistant to organic solvents; Flammable. Aperture diameter 5.0mm for the initial injection, 0.8mm for fine filtration, 0.45mm can filter out most bacteria, 0.15mm can filter out pyrogen.
(C) Ultraviolet sterilization: Wavelength 200 ~ 300nm, easy to penetrate clean water and air, used for surface sterilization of air and objects. Ultraviolet lamps are generally valid for 3,000 hours. The ultraviolet radiation exposure time to the microbe killing rate is shown in the table:
Irradiation time (hours) Kill rate (%)
Typhoid bacillus Escherichia coli Staphylococcus aureus Yeast
0.5 33 33.5 30.6 19.9
1.0 42 43 41 35.6
1.5 65 58 59 43.8
2.0 86 80 82 69.5
2.5 100 95.5 96.3 80
3.0 100 100 90.6
4.0 99
5.0 100
(D) Microwave Sterilization: Electromagnetic waves of 300 to 3000 MHz. Water can strongly absorb microwaves, causing polar molecules to rub and produce heat. Can penetrate deeper parts, sterilization effect is good. Expected for the sterilization of injections.
(v) Shot Sterilization: Also known as ionizing radiation, it is sterilized by g-ray or b-ray irradiation. The former is emitted from cobalt-60 or caesium-137, which has strong penetrability; the latter is generated by an electron accelerator, has a charge, has weak penetrating power, and has a poor sterilization effect. For radiation, no bacillus is much more sensitive than bacillus; gram-negative bacteria are more sensitive than positive bacilli in bacillus-free bacteria; and the virus sensitivity is poor. In addition, radiation can cause changes in the pH, content, and activity of some drugs, and some products should not be used.
Second, chemical sterilization method:
It is generally sterilized by spraying (mist) and evaporation.
(a) ethylene oxide: colorless ether-like odor gas, boiling point 10.8 °C, the following boiling point is colorless transparent liquid, specific gravity 0.882, soluble in water. Diffusion penetration ability, is a broad-spectrum fungicide. For the sterilization of heat-sensitive drugs, plastics, rubber, leather products, leather, paper and small glassware.
(B) Peracetic acid: colorless and transparent liquid with irritating odor and odor of acetic acid, volatile and corrosive. Soluble in water, ethanol, ether, acetic acid. It can slowly decompose and explode when exploded rapidly. However, solutions below 40% will not. This product is broad-spectrum, high-efficiency, quick-acting, low toxicity, 0.5% solution is used for air (spray 30ml/m3), equipment and skin disinfection, preparation before use.
(c) Others:
1, phenol (carbolic acid): 3 to 5% of the ground, the wall sprinkled.
2, cresol soap solution (Lysule): 5 to 100% of the ground, sprayed on the wall.
3, formaldehyde solution (formalin): 20ml/m3 heating evaporation, 6 to 12 hours.
4, lactic acid: 1ml/m3 heating evaporation 0.5 ~ 1 hour.
5, benzalkonium bromide: 1/1000 ~ 1/2000 solution sprayed the ground, walls.
6, propylene glycol: 1ml/m3 heating evaporation.
Third, air cleaning technology: to ensure product purity and improve product yield.
(A) General standards for clean rooms: the following table
Production Area Classification Clean Grade (Grade) ≥ 0.5mm Particles (Units/L) Colony Count Example
General production area Production and auxiliary workshop without cleanliness requirements
Control area > 100,000 or 300,000 <35,000 Tablets, capsules, etc.; crushing, batching, dispensing, coating raw material essence, baking, bag, powder needles, etc.
100,000 ≤3.500 ≤10 Bottle fine washing, filtration membrane assembly, weighing, concentrated dispensing, etc.
Clean Area 10,000 ≤350 ≤3 Aseptic raw material crystallization, drying, powder injection raw materials sifting, mixing powder, dilute distribution, filtration, direct contact with the drug packaging material final processing positions.
All or part of 100 ≤ 3.5 ≤ 1 large infusion, injection, packaging, plugging; strains inoculation table
(B) Cleanroom Management: Cleanrooms are important facilities for improving and guaranteeing the quality of production outlets. They must have strict management and hygiene requirements.
1. The staff must have a wide understanding of the importance of the clean room and the entire installation system;
2, should develop clean room management, use, sterilization system;
3, women can not use powder, hair spray, nail polish and other cosmetics to reduce the source of pollution;
4. Operators should minimize speech and indoor activities;
5. Work clothes should use polyester and nylon fabrics that are not prone to static electricity and do not easily fall off.
6, regular cleaning and sterilization. The interior is kept clean and tidy, and the walls and equipment are regularly cleaned to ensure that there is no dust and so on.
Several sterilizing technologies and equipment applications in the food industry today
One of the purposes of food processing is to protect and preserve foods, kill microorganisms, and inactivate enzymes. The main reason for food spoilage is the presence of certain microorganisms and fungi, which causes great losses each year. Sterilization is a necessary process for food processing. However, the traditional heat sterilization can not kill all the microorganisms in the food, especially some heat-resistant Bacillus; at the same time, the heating will destroy the nutrients and the natural characteristics of the food in different degrees. In order to keep the natural color, fragrance, taste and some physiological active ingredients of foods to a greater extent, and meet the living requirements of modern people, a new type of sterilization technology has emerged. This article mainly introduces the new sterilization technology in the food field in the world and its China's development and application status.