Heat sterilization is divided into low-temperature sterilization, high-temperature sterilization, ultra-high temperature instant sterilization and aseptic filling (filling), etc. I wonder which category the poster is talking about?
Pasteurization is a disinfection method that uses heat below 100 degrees Celsius to kill microorganisms. It was invented by the German microbiologist Pasteur in 1863. It is still widely used at home and abroad in milk, Sterilization of human milk and synthetic infant foods.
The biologically active substances in fresh raw milk are very resistant to heat. If the sterilization method of 100 degrees Celsius is used, the biologically active substances in the raw milk will be destroyed, and the vitamins, proteins, etc. in the raw milk will also be damaged. loss.
Pasteur has proved through a large number of scientific experiments that if the temperature of raw milk exceeds 85°C, the nutrients and biologically active substances in it will be greatly destroyed, but if the temperature is lower than 85°C, its nutrients will be destroyed. Nutrients and biologically active substances are retained, and most harmful bacteria are killed, while some beneficial bacteria remain. Therefore, the sterilization method below 85℃ is called pasteurization. It can be said that this is the most scientific and best processing technology for fresh milk. The nutritional value and health care functions of fresh milk produced by pasteurization are basically the same as fresh raw milk.
There are generally two currently used pasteurization methods: one is to heat to between 61.1 and 65.6 degrees Celsius for 30 minutes; the other is to heat to 71.7 degrees Celsius and hold for at least 15 seconds.
Due to the low temperature achieved by pasteurization, the degree of sterilization cannot be achieved. However, it can kill pathogenic microorganisms such as Brucella, Mycobacterium tuberculosis, Shigella, and Typhoid, and can reduce the total number of bacteria by 90%-95%, so it can reduce the spread of diseases and extend the use time of items. In addition, this sterilization method will not destroy the active ingredients of sterilized food, and the method is simple.
The following is about the origin of "pasteurization":
In 1865, the famous French chemist Louis Pasteur (known as the "father of modern microbiology") When Louis Pasteur was solving the problem of abnormal fermentation of wine, he discovered that heating could kill harmful microorganisms. He later used this method to produce safe "sterilized milk", which extended the shelf life of milk to dozens of hours. This process was It is called "pasteurization method"
Food resistance heating sterilization technology
1. The basic concept of resistance heating technology (ohmic heating, also known as ohmic heating)
< p>1. Characteristics of resistance heating technologyIn recent years, it has received widespread attention in the field of foreign food processing. This heating method is completely different from the traditional food heating method. It passes electric current through the food and uses its electrical impedance to generate heat energy to heat the food. It is mainly aimed at the aseptic processing of liquid food containing particles and solves the problem of heating and sterilization between liquid and solid particles. Uneven problem.
2. Development of resistance heating technology
The development and design of continuous resistance heaters was started by the British Electrical Research and Development Center. It obtained a patent in the 1980s and manufactured commercial resistors in the 1990s. Heating system.
2. Principle of resistance heating technology
Resistance heating technology uses alternating current to pass through food. Because the salts or organic acids contained in food are electrolytes, regardless of fluid or solid current All can be passed. Heat is generated inside the food. The principle is to use the electrical conductivity of the food itself and the large electrical impedance characteristics of poor conductors to generate heat energy. When resistance electric heating technology is applied to food containing granular fluids, its heating form is obviously different from traditional heating methods. Different from traditional steam heating, the temperature of solid particles must be lower than the temperature of the liquid. Conversely, during resistance heating, the temperature of the solid particles is often equivalent to the temperature of the surrounding liquid, and sometimes even exceeds the temperature of the liquid. It can be seen from this that there has been a breakthrough development in resistance heating technology for food containing fluids containing particles (especially those with low acidity). Currently, resistance heating technology has commercial production equipment in Europe and Japan, and the United States has also agreed to use resistance heating technology for food containing fluids containing particles. Commercial sterilization techniques for food.
3. Heat transfer method of resistance heating technology
Looking at the heat transfer mode of product heating and sterilization, traditional sterilization technology, whether it is packaging first and then sterilization or first After sterilization and packaging, the heating medium is steam.
The heat transfer method is that the heat medium first heats the fluid through heat exchange, and then the carrier liquid transfers the heat energy to the solid particles in a convection manner, and then the particles themselves transfer the heat energy to the solid center by thermal conduction, so there is a heat transfer speed. The problem of slow and uneven heating is that in order to achieve sufficient sterilization conditions at the center point of the particles, it is usually necessary to sacrifice the quality of the liquid and overheat it, resulting in a decrease in quality and loss of flavor and nutrients.
During resistance heating, solid particles are heated directly, and the inside and outside of the solid particles can be heated simultaneously with almost no heat transfer. The temperature of the solid particles is often equivalent to the temperature of the surrounding liquid, and sometimes even exceeds the temperature of the liquid. temperature. Ohmic heating converts electrical energy into thermal energy that spreads throughout the heated object, and there is no obvious limit to the depth of penetration. The heating sterilization effect is uniform, which is beneficial to improving product quality.
IV. Precautions when using resistance heating technology
① Whether food is suitable for ohmic heating depends on the conductivity of the food. Insulators cannot be directly heated by ohmic heating, such as non-ionized nonvalent bond fluids such as grease, ethanol, syrup, and non-metallic solid materials such as bone components, cellulose, ice crystals, etc. Most foods contain free water in which some amount of ionic salt has been dissolved, and thus become a conductor.
② Foods that can be pumped have a moisture content of more than 30% and are conductive, so ohmic heating can be effectively used for sterilization.
③ In the ohmic heating method, in order to increase the conductivity, it is generally not suitable to use unsalted tap water.
5. Factors affecting resistance heating technology
1. Temperature
During the heating process, the higher the temperature of the food raw materials, the higher the conductivity; heating The rate increases with the temperature of the food ingredients.
2. Electrolyte concentration
Particles with high electrolyte concentration have high electrical conductivity, resulting in higher heating speed. Usually, granular food is first soaked in saline solutions of different concentrations to increase the electrolyte content of the granules, and then resistively heated.
In addition, if the granules are preheated first and then resistively heated, the conductivity will be higher. Its heating rate also increases. Because preheating destroys cell tissue to some extent, the fluidity of water inside the particles increases.
6. Conditions that resistance heating equipment must meet
(1) The electrical design of the system must avoid causing food electrolysis and contamination caused by electrode dissociation or local overheating and burning of food. Food;
(2) Ability to effectively control the heating rate and flow rate of food;
(3) Sterile packaging capable of filling and sealing granular fluid food in a sterile environment Technology;
(4) System equipment investment and operating costs are acceptable.
7. Advantages of resistance heating technology
① It can produce fresh, solid-containing products with high nutritional value;
② There is no heat conduction interface, so Can be heated continuously;
③ Can process delicious food;
④ Less pollution;
⑤ Rapidly and uniformly heats fluids and solids with minimal thermal damage and The shortest processing time;
⑥The production is very quiet;
⑦The maintenance cost is low;
⑧The start and stop operations are simple, and the processing control is convenient;
⑨ It has the possibility of reducing pre-processing, manufacturing and packaging costs.
⑩The thermal energy conversion rate of this method can be as high as 90%, while the thermal energy efficiency of other methods is only 45-50%.
The above can become low-temperature sterilization.
High temperature sterilization is as follows:
Food resistance heating sterilization technology
1. The basic concept of resistance heating technology (ohmic heating, also known as ohmic heating)< /p>
1. Characteristics of resistance heating technology
In recent years, it has received widespread attention in the field of foreign food processing. This heating method is completely different from the traditional food heating method. It passes electric current through the food and uses its electrical impedance to generate heat energy to heat the food. It is mainly aimed at the aseptic processing of granular fluid food and solves the problem of heating sterilization between liquid and solid particles. Uneven problem.
2. Development of resistance heating technology
The development and design of continuous resistance heaters was started by the British Electrical Research and Development Center. It obtained a patent in the 1980s and manufactured commercial resistors in the 1990s. Heating system.
2. Principle of resistance heating technology
Resistance heating technology uses alternating current to pass through food. Because the salts or organic acids contained in food are electrolytes, regardless of fluid or solid current All can be passed. Heat is generated inside the food. The principle is to use the electrical conductivity of the food itself and the large electrical impedance characteristics of poor conductors to generate heat energy. When resistance electric heating technology is applied to liquid foods containing particles, the heating form is obviously different from traditional heating methods. Different from traditional steam heating, the temperature of solid particles must be lower than the temperature of the liquid. Conversely, during resistance heating, the temperature of the solid particles is often equivalent to the temperature of the surrounding liquid, and sometimes even exceeds the temperature of the liquid. It can be seen from this that there has been a breakthrough development in resistance heating technology for food containing fluids containing particles (especially those with low acidity). Currently, resistance heating technology has commercial production equipment in Europe and Japan, and the United States has also agreed to use resistance heating technology for food containing fluids containing particles. Commercial sterilization techniques for food.
3. Heat transfer method of resistance heating technology
Looking at the heat transfer mode of product heating and sterilization, traditional sterilization technology, whether it is packaging first and then sterilization or first After sterilization and packaging, the heating medium is steam. The heat transfer method is that the heat medium first heats the fluid through heat exchange, and then the carrier liquid transfers the heat energy to the solid particles in a convection manner, and then the particles themselves transfer the heat energy to the solid center by thermal conduction, so there is a heat transfer speed. The problem of slow and uneven heating is that in order to achieve sufficient sterilization conditions at the center point of the particles, it is usually necessary to sacrifice the quality of the liquid and overheat it, resulting in a decline in quality and loss of flavor and nutrients.
During resistance heating, solid particles are heated directly, and the inside and outside of the solid particles can be heated simultaneously with almost no heat transfer. The temperature of the solid particles is often equivalent to the temperature of the surrounding liquid, and sometimes even exceeds the temperature of the liquid. temperature. Ohmic heating converts electrical energy into heat energy that spreads throughout the heated object, and there is no obvious limit to the depth of penetration. The heating sterilization effect is uniform, which is beneficial to improving product quality.
IV. Precautions when using resistance heating technology
① Whether food is suitable for ohmic heating depends on the conductivity of the food. Insulators cannot be directly heated by ohmic heating, such as non-ionized nonvalent bond fluids such as grease, ethanol, syrup, and non-metallic solid materials such as bone components, cellulose, ice crystals, etc. Most foods contain free water in which some amount of ionic salt has been dissolved, and thus become a conductor.
② Foods that can be pumped have a moisture content of more than 30% and are conductive, so ohmic heating can be effectively used for sterilization.
③ In the ohmic heating method, in order to increase the conductivity, it is generally not suitable to use unsalted tap water.
5. Factors affecting resistance heating technology
1. Temperature
During the heating process, the higher the temperature of the food raw materials, the higher the conductivity; heating The rate increases with the temperature of the food ingredients.
2. Electrolyte concentration
Particles with high electrolyte concentration have high electrical conductivity, resulting in higher heating speed. Usually, granular food is first soaked in saline solutions of different concentrations to increase the electrolyte content of the granules, and then resistively heated.
In addition, if the granules are preheated first and then resistively heated, they will have a higher conductivity. Its heating rate also increases. Because preheating destroys cell tissue to some extent, the fluidity of water inside the particles increases.
6. Conditions that resistance heating equipment must meet
(1) The electrical design of the system must avoid causing food electrolysis and contamination caused by electrode dissociation or local overheating and burning of food. Food;
(2) Ability to effectively control the heating rate and flow rate of food;
(3) Sterile packaging capable of filling and sealing granular fluid food in a sterile environment Technology;
(4) System equipment investment and operating costs are acceptable.
7. Advantages of resistance heating technology
① It can produce fresh, solid-containing products with high nutritional value;
② There is no heat conduction interface, so Can be heated continuously;
③ Can process delicious food;
④ Less pollution;
⑤ Rapidly and uniformly heats fluids and solids with minimal thermal damage and The shortest processing time;
⑥The production is very quiet;
⑦The maintenance cost is low;
⑧The start and stop operations are simple, and the processing control is convenient;
⑨ It has the possibility of reducing pre-processing, manufacturing and packaging costs.
⑩The thermal energy conversion rate of this method can be as high as 90%, while the thermal energy efficiency of other methods is only 45 to 50%.
I hope you can find a suitable answer.