Food Sterilization Technology Encyclopedia

Food sterilization technologies mainly include heat sterilization and non-heat sterilization. Among them, heat sterilization mainly includes: moist heat sterilization, dry heat sterilization, microwave sterilization, electric heat sterilization, electric field sterilization, etc.; non-thermal sterilization mainly includes: chemical and biological sterilization, radiation sterilization, UV sterilization, pulse sterilization, ultra-high static pressure sterilization, pulse electric field (PEF) sterilization and vibration magnetic field sterilization, etc. Here is a detailed introduction to these sterilization technologies (Encyclopedia of Food Sterilization Technologies):

damp heat sterilization:

Heat sterilization is a form of heat treatment whose main purpose is to kill microorganisms, and moist heat sterilization is one of the most important methods. It is a sterilization method that uses steam and hot water as the heating medium, or directly uses steam jet heating.

Using a thermal energy converter (such as a boiler) to convert the burning heat energy into hot water or steam as a heating medium, and then use a heat exchanger to transfer the heat energy of the hot water or steam to the food, or spray steam directly into the food to be heated.

Commonly used heating media in food heat treatment and their characteristics

Heating agent type Heating agent characteristics

Steam is easy to be transported by pipes, heating is uniform, temperature is easy to control, latent heat of condensation is large, but the temperature should not be too high

Hot water is easy to be transported by pipes, evenly heated, and the heating temperature is not high

Air heating temperature can be very high, but its density is low, and the heat transfer coefficient is low

Flue gas heating temperature can reach very high, but its density is low, heat transfer coefficient is low, it may contaminate food

Gas heating temperature can reach high, low cost, but may contaminate food

Electric heating temperature can be very high, temperature is easy to control, but high cost

1. The effect of heating on microorganisms

(1) Microorganisms and food spoilage

Microorganisms in food are the main cause of food intolerance. Bacteria, molds and yeasts can all cause food spoilage.

bacteria, mold and yeast

Microorganisms in food are the main cause of food intolerance. Generally speaking, food materials contain microorganisms. In the process of food harvesting, transportation, processing and preservation, food may also contaminate microorganisms. Under certain conditions, these microorganisms will grow and multiply in food, causing the food to lose its original or due nutritional value and sensory quality, and even produce harmful and toxic substances.

Bacteria, mold and yeast map

Bacteria, mold and yeast may all cause food spoilage, and bacteria are the main microorganisms that cause food spoilage. Among the bacteria, non-spore bacteria have the most types in nature and have the greatest possibility of contaminating food. However, these bacteria are not strong in heat resistance and pasteurization can kill them. Bacillus is the most heat-resistant bacteria. Bacillus is also divided into aerobic, anaerobic and facultative anaerobic. Aerobic and facultative anaerobic spores are responsible for the spoilage of canned food. Clostridium botulinum in anaerobic spores is often the target bacteria for canned food. The spoilage caused by yeasts and molds mostly occurs in foods with higher acidity. Some yeasts and molds are also more resistant to osmotic pressure.

(2) Growth temperature of microorganisms

The optimum growth temperature of different microorganisms is different. When the temperature is higher than the optimum growth temperature of the microorganism, the growth of the microorganism will be inhibited, and when the temperature is high enough to denature the protein in the microorganism, the microorganism will die .

Minimum growth temperature Optimum growth temperature Maximum growth temperature

Thermophilic bacteria 30～45 50～70 70～90

mesophilic bacteria 5～15 30～45 45～55

Low temperature bacteria -5～5 25～30 30～55

psychrotrophic bacteria -10～-5 12～15 15～25

The optimum growth temperature and thermal lethal temperature of microorganisms (℃)

(3) Heat resistance of spoilage bacteria under humid and hot conditions

It is generally believed that the ability of protein in microbial cells to freeze and lose metabolism by heating is the cause of the death of microorganisms. Therefore, the degree of ease of heat coagulation of intracellular proteins is directly related to the heat resistance of microorganisms. The thermal coagulation conditions of protein are affected by other conditions, such as acid, alkali, salt and moisture.

(4) Factors affecting the heat resistance of spoilage bacteria

1. Before heating-the influence of the cultivation and experience of spoilage bacteria on its heat resistance

Influencing factors mainly include: the heredity, composition, and morphology of the cell itself, the composition of the culture medium, the environmental factors during cultivation, the temperature during development, and metabolites.

Mature cells are more heat-resistant than immature cells. The higher the culture temperature, the stronger the heat resistance of the spores, and the bacterial spores cultivated at the optimum temperature have the strongest heat resistance. The spores developed in a nutrient-rich medium have strong heat tolerance, but weaker when the nutrient is lacking.

2. When heating-heating temperature, heating lethal time, cell concentration, presence or absence of cell clumps, medium properties and pH value and other factors affect the heat resistance of spoilage bacteria.

(1) Heating conditions: At a certain thermal lethal temperature, bacteria (spores) die in a logarithmic pattern with time; the higher the temperature, the shorter the time required to kill it.

(2) Bacterial status: Under a certain heat lethal temperature, the more bacteria count, the longer it takes to kill it. The presence of cell clumps reduces the effect of heat sterilization

(3) Media properties: including water (water activity), pH, carbohydrates, lipids, proteins, inorganic salts, etc., are the most important factors affecting the sterilization effect.

(4) The influence of various additives, preservatives and fungicides

3. After heating--test of the heat death effect

Spoilage bacteria have the following manifestations after heat damage: the induction period during development is prolonged, and the nutritional requirements are increased; the optimal pH range during development is reduced; the optimal temperature range during proliferation is reduced; the sensitivity to inhibitors is enhanced; the intracellular substances leak Increased sensitivity to radiation; decreased enzyme activity in cells; RNA decomposition of nucleic acid bodies, etc.

To determine whether the spoilage bacteria have been killed, the heat-killing effect needs to be measured. The heat-treated bacterial spores are often re-cultured to check whether they are still alive. Choose an appropriate medium. If the spoilage bacteria do not grow again, the sterilization process is suitable.

(1) Reaction rate of thermal destruction reaction

The thermal destruction reaction of each ingredient in food generally follows first-order reaction kinetics, that is to say, the thermal destruction reaction rate of each ingredient is proportional to the concentration of the reactant. This relationship is often referred to as the "logarithmic order of inactivation or destruction". This relationship means that at a certain heat treatment temperature (a temperature sufficient to achieve thermal inactivation or thermal destruction), the proportion of food ingredients that are inactivated or destroyed per unit time is constant.

DT value

is the Decimal reduction time, which is the negative reciprocal of the slope of the thermal lethal rate curve. It can be considered as the time required for every 90% reduction in viable bacteria (or spores) at a certain temperature, usually in minutes.

Since the above lethal rate curve is obtained at a certain heat treatment (lethal) temperature, in order to distinguish the D value of microorganisms at different temperatures, the general heat treatment temperature T is used as a subscript and marked on the D value, which is DT. Obviously, the value of D can reflect the heat resistance of microorganisms. When comparing the D values ​​of different microorganisms at the same temperature, the larger the D value, the longer it takes to kill 90% of the microorganisms at that temperature, that is, the more heat-resistant the microorganisms are.

It must be pointed out that the DT value is not affected by the original bacterial count, but it varies with the heat treatment temperature. The higher the temperature, the greater the rate of microbial death, and the smaller the DT value.

TDT value

is the thermal death time (Thermal death time). When the bacteria are heat-treated within a certain period of time (usually 1-10 minutes), the temperature of each heating period starting from the lowest heat treatment temperature at which the bacteria die is called the thermal lethal temperature.

Under a certain constant temperature (thermal lethal temperature), the time (min) required to kill a certain concentration of a certain microbial viable bacteria (bacteria and spores) in food is generally expressed by TDT value, which is also on the right The sterilization temperature is marked on the lower corner.

F value

F value, also known as sterilization value, refers to the time (min) required to kill a certain number of certain microorganisms at a certain lethal temperature. Since the type and temperature of microorganisms are specific, usually F-values ​​should be marked with superscripts and subscripts for easy distinction, namely. Generally, under standard sterilization conditions, it is recorded as the heat death time of spoilage bacteria at F0 at a heat death temperature of 121.1℃, usually expressed by F value. The F value can be used to compare the heat resistance of spoilage bacteria at the same Z value. It is related to the original number of bacteria in the heat death test, and varies with the specified temperature, strain, strain and environment.

Z value

The temperature value that needs to be increased or decreased when the thermal death time is reduced by 1/10 or increased by 10 times, generally expressed by the Z value. The Z value is a measure of the change in the rate of microbial death when the temperature changes.

TRT value

is the decreasing time of thermal index. The heat treatment time required to reduce the number of bacteria or spores to 10-n at a specific heat death temperature. It refers to the time (min) required to reduce the number of viable microbes to a certain degree, such as 10-n or 1/10n (that is, 1/10n of the original viable number) under a certain lethal temperature, which is recorded as TRTn , The unit is minutes, and n is the decreasing exponent.

obviously: . It can be seen that the TRT value is not affected by the original number of viable microorganisms, and it can be used as a basis for determining the sterilization process conditions, which is more convenient and advantageous than using the aforementioned TDT value affected by the number of original viable microorganisms. The value of TRTn will vary with temperature just like the value of D. When n=1, TRT1=D. If the logarithmic value of D is taken as the ordinate and the heating temperature T is the abscissa, according to the relationship between D and T, a curve similar to the pseudo-thermal lethal time curve can be obtained, also known as the TRT1 curve.

low temperature and long-term sterilization

(一) concept

low-temperature long-term sterilization is also called pasteurization. Compared with commercial sterilization, pasteurization is a milder form of heat sterilization. The processing temperature of pasteurization is usually below 100℃. The typical pasteurization condition is 62.8℃/30min, which can achieve the same pasteurization. The sterilization effect can have different temperature and time combinations. Pasteurization can inactivate enzymes in food and destroy heat-sensitive microorganisms and pathogenic bacteria in food. The purpose of pasteurization and the storage period of its products mainly depend on the sterilization conditions, food ingredients (such as pH) and packaging conditions. For low-acid foods (pH>4.6), its main purpose is to kill pathogenic bacteria, and for acidic foods, it also includes killing spoilage bacteria and inactivating enzymes.

(2) Features

①Simple and convenient, the bactericidal effect is 99%, and the pathogenic bacteria are completely killed;

② can not kill thermophilic, heat-resistant bacteria, spores, and some remaining enzymes;

③The equipment is huge and the sterilization time is longer;

High temperature and short time sterilization method

(一) concept

High temperature short-time sterilization mainly refers to the sterilization treatment of food above 100°C and below 130°C. Mainly used in the sterilization of low-acid food with pH>4.5.

(2) Features

①Small footprint, compact (only 20% of the footprint of the single-cylinder method)

②Large processing capacity, continuous production, saving heat source and low cost;

③It can be operated under confined conditions to reduce the chance of pollution. However, the residual number of bacteria after sterilization will be higher than that of low-temperature and long-term sterilization;

④The heating time is short, the loss of nutrients is small, the milk quality is high, and there is no stewed taste;

⑤ It can be matched with CIP (in-situ non-disassembly circulating cleaning system) cleaning, saving labor and improving efficiency;

⑥The temperature control and detection system requires strict requirements (the instrument must be accurate)

(3) Applicable scope of equipment

requires fast and effective heat transfer, and scraper or tube heat exchangers are usually used. This method is suitable for liquid or small particle mixtures. But if it is a very viscous liquid or the particle diameter is greater than 3cm, the heating will be controlled by heat conduction. At this time, the product needs to be heated for several minutes to meet the sterilization requirements, so the product quality, nutritional content and taste will be affected.

usually use hot water or steam heating tube or scraper heat exchanger.

Ultra-high temperature instant sterilization

Features

①Accurate temperature control and precise equipment;

②The temperature is high, the sterilization time is extremely short, the sterilization effect is significant, and the chemical changes caused are few;

③Suitable for continuous automated production;

④The consumption of steam and cold source is higher than the high temperature short-time sterilization method HTST.

steam jet heating sterilization method

(一) concept

refers to the UHT sterilization method using steam injection, usually called direct steam injection or DSI.

In the final sterilization stage, the product is mixed with steam under a certain pressure, and the steam releases latent heat to quickly heat the product to the sterilization temperature. This direct heating system heats the product faster than any other indirect system.

(2) Features

1. The heating and cooling speeds are faster, and the UHT instantaneous heating is easier to achieve through the direct heating system.

2. It can process products with high viscosity, especially for those products that cannot be processed well through the plate heat exchanger, it is not easy to form fouling. But the steam pressure will limit the long-term operation of the equipment.

3. After the product is sterilized, it is necessary to perform aseptic homogenization, which greatly increases the cost and operating cost of the equipment itself.

4. The structure is complex, most of the devices are non-standard, and the system cost is twice that of a plate or tube heating system with the same processing capacity.

5. The operating cost is high, and the limitation of energy recovery increases the heating cost. But to a certain extent, the system can run continuously for a long time to make up for its high cost defects. Especially for milk, the indirect system will cause serious scaling, and the direct heating system is more in line with the product characteristics and quality requirements.

secondary sterilization

(一) concept

The secondary sterilization method can be divided into batch type and continuous type according to the equipment operation mode.

Intermittent means that the product is sterilized for the first time with a tubular ultra-high temperature sterilizer, then filled and capped, and then put into the intermittent sterilizer for the second sterilization.

Continuous type means that the first sterilization of the product uses a tube or plate ultra-high temperature sterilizer, and the second sterilization uses a continuous sterilizer. The product sterilized by this method has a long shelf life, which is conducive to long-distance storage and transportation.

(2) Features

1. The intermittent secondary sterilization method has simple equipment and low investment, but the product quality is unstable.

2. The continuous secondary sterilization line is characterized by large investment, high output and stable product quality.

3. The secondary sterilizer is the core equipment of the secondary sterilization production line. It requires rapid heating and cooling, uniform heat transfer, minimized thermal shock and thermal inertia, good performance, and strict implementation of sterilization procedures.

The choice of sterilization method

The following basic principles should be followed when choosing heat sterilization methods and conditions:

(1) The corresponding heat treatment purpose should be achieved

1. Mainly processing:

The food after heat treatment should meet the requirements of heat processing.

2, with preservation as the main purpose:

The food after heat treatment should achieve the corresponding purpose of sterilization and inactivation of enzymes.

(2) The damage and loss of food nutrients caused by heat treatment should be minimized

The heat treatment process should pay attention to the transfer characteristics and actual effects of heat energy in food, meet the requirements of food hygiene, and should not produce harmful substances. The optimization method should be selected according to the purpose of product heat treatment.

Some optimization methods of heat treatment

Types of heat treatment optimization method

Hot Scalding Consider the loss of nutrients caused by non-heat loss (such as leaching, oxidative degradation, etc.).

Pasteurization If there is no heat-resistant enzyme in the food, try to use high temperature and short-time process.

Commercial sterilization For products with convective heat transfer and aseptic packaging, when heat-resistant enzymes do not become the main factor affecting the process, try to use high temperature and short-time processes. For products that conduct heat transfer, it is generally difficult to use high-temperature short-time processes.

The transfer of heat energy in food

Two aspects of information must be known when calculating the effect of heat treatment, one is the heat resistance parameters of food ingredients such as microorganisms, and the other is the temperature change process of the food during the heat treatment.

(1) Heat transfer of the food in the can

The factors that affect the heat transfer of the food in the container include: surface heat transfer coefficient; the physical properties of the food and the container; the temperature difference between the temperature of the heating medium (steam) and the initial temperature of the food; the size of the container.

To accurately evaluate the degree of heating of canned food during heat treatment, it is necessary to find the temperature point that can represent the temperature change of the food in the can. Usually people choose the cold point temperature with the slowest temperature change in the can. The temperature of the point is the lowest (also called the lowest heating point at this time, Slowest heating point), and the temperature of this point is the highest during cooling. During the heat treatment, if the food in the cold spot meets the heat treatment requirements, the food in other places in the tank must also meet or exceed the required heat treatment degree.

The location of the cold spot of the can is related to the heat transfer of the food in the can.

1. Canned food with conduction heat transfer method:

Because the heat transfer process is from the tank wall to the center of the can, the cold spot of the can is at the geometric center of the can.

2. Canned food with convective heat transfer:

Due to the convection of the food in the can, the hot food rises and the cold food falls, the cold spot of the can will move downward, usually at a certain position below the geometric center of the can on the central axis of the can.

3. Canned food with mixed heat transfer by conduction and convection:

Its cold spot is between the above two.

(2) Data for evaluating heat penetration

The measurement of heat transfer during heat treatment should be based on the temperature change of the cold spot. Usually the thermometer uses copper? Constantan as a thermocouple to measure the potential difference when there is a temperature difference between the two points, and then convert it to temperature. principle.

When evaluating the effect of heat treatment (such as calculating the bactericidal strength F value by the general method), it is necessary to use the relevant data of heat penetration. At this time, the heat transfer curve inside the can should be drawn first to find the relevant characteristic value.

heat transfer curve

The heat transfer curve is the curve obtained by plotting the change of the cold spot temperature (Tp) in the tank with time on a semi-logarithmic coordinate. When drawing, use the logarithm of the difference (Th-Tp or Tp-Tc) between the cold spot temperature and the heating temperature (Th) or cooling temperature (Tc) in the sterilization pot as the ordinate, and the time as the abscissa to obtain the corresponding heating Curve or cooling curve. In order to avoid expressing the temperature difference on the coordinate axis, the graph paper used to mark the heat transfer curve can be turned upside down 180 degrees, and the ordinate is marked with the corresponding cold spot temperature (Tp).

Taking the heating curve as an example, the starting point of the ordinate is Th-Tp =1 (theoretically, at the end of heating, Tp may be very close to Th, but Th-Tp ≠ 0), and the corresponding Tp value is Th-1, that is, the vertical The temperature marked by the highest line on the coordinate should be one degree (℃) lower than the sterilization temperature, the coordinate value interval of the first logarithmic period coordinate is 1℃, and the coordinate value interval of the second logarithmic period coordinate is 10℃, and so on. Mark the remaining temperature values.

Calculation of sterilization conditions

The conditions for heat sterilization of food are mainly sterilization value and sterilization time. There are currently three widely used calculation methods: improved basic method, formula method and nomographic method.

(1) Improved Basic Law

In 1920, Bigelow first established the canned sterilization theory, and proposed the basic method for estimating sterilization time (The general mathod), also known as the basic inference algorithm. This method puts forward the concept of partial sterilization rate. It calculates the total lethal effect of the entire heat sterilization process by calculating the lethality rate at different temperature-time combinations in the entire heat sterilization process including the heating and cooling stages. In 1923, Ball developed an improved general method based on the heating effect of the canned food center during the heat sterilization process using integrals to calculate the sterilization effect. This method improves the accuracy of calculation and becomes a widely used method.

In the process of sterilization, the temperature of food will change continuously with the change of sterilization time. When the temperature exceeds the lethal temperature of microorganisms, the microorganisms will die. Different temperatures have different rates of microbial death. There is a certain sterilization effect after staying at lethal temperature for a period of time. The entire sterilization process can be regarded as the sum of the sterilization effects obtained by staying at different sterilization temperatures for a period of time.

(2) Formula calculation method

This method was proposed by Bauer and was simplified by the Thermal Engineering Research Group of the American Can Company to calculate the sterilization time and F value on the simple and transition heat transfer curves. Although simplification may introduce some errors, it has little effect. This law has been included in the relevant regulations of the US FDA and is widely used in the United States.

The 　　 formula method is based on the heating curve drawn on semi-logarithmic graph paper based on the temperature change of the can content during the sterilization process, and the curve where the cooling water immediately enters the sterilization pot for cooling at the end of the sterilization process to calculate and find the answer. Its advantage is that the sterilization time can be calculated when the sterilization temperature is changed. Its disadvantage is that the calculation is cumbersome and time-consuming, and it is also prone to errors in the calculation. It also requires that the heating curve must be a regular simple heating curve or a turning heating curve. Seek more correct results.

In recent decades, many scholars have conducted research on this method in order to achieve the purpose of being correct, simple, and convenient to use. With the application of computer technology, the formula method is as accurate as the improved application method, but faster and more concise.

(Three) nomogram

nomogram method is to make relevant parameters into a nomogram calculation diagram, and use the diagram to calculate the sterilization value and sterilization time. This method is suitable for any simple heating curve with Z=10℃ and m+g=76.66℃, which is quick and convenient, but it cannot be used for the calculation of transition heating curve. When the relevant data goes beyond the line, it cannot be calculated by this method.

Determination of sterilization conditions

When determining the heat sterilization conditions of food, various factors affecting heat sterilization should be considered. The main purpose of heat sterilization of food is sterilization and enzyme inhibition. It should be based on the heat resistance of microorganisms and enzymes, and according to the actual heat transfer during heat treatment, select food heat sterilization conditions to determine the minimum degree of heat treatment to achieve sterilization and enzyme inhibition . The research trend of heat sterilization technology is concentrated on the optimization of heat sterilization conditions, the development of new heat sterilization methods and equipment. The optimization of heat sterilization conditions is to coordinate the temperature and time conditions of heat sterilization, so that the heat sterilization can reach the desired goal, while minimizing unnecessary effects.

The method and technology of heat sterilization are closely related to the sterilization equipment. Good sterilization equipment is a necessary condition to ensure perfect sterilization operation. There are many types of sterilization equipment currently in use, and the heating medium and heating method used by different sterilization equipment, the achievable process conditions and the degree of automation are not the same. In addition to heating and cooling devices, sterilization equipment generally also has feeding and discharging (tank) transmission devices, safety devices and automatic control devices.

related equipment and devices

Intermittent Continuous

Vertical sterilization pot 　　　　　　 Spray continuous sterilization machine

horizontal sterilization pot 　　　　　　 hydrostatic pressure sterilizer

Water-drenching sterilization pot 　　　　　 Water-sealed continuous high pressure sterilization pot

Full water rotary sterilizer 　　 　Ultra-high temperature instantaneous sterilization machine

The determination of heat sterilization conditions for canned food

(1) Full tank test

The goal is to satisfy the theoretically calculated sterilization value (F0), and heat sterilization can have various combinations of sterilization temperature and time.

The purpose of the full can test is to select the sterilization conditions according to the comprehensive factors such as the quality of the canned food and the production capacity, so that the heat sterilization can not only meet the requirements of sterilization safety, but also maintain its high quality, which is the most economically reasonable.

(2) Sterilization test of real pot inoculation

Inoculate the bacteria or spores that commonly cause canned spoilage into the cans quantitatively, sterilize them for different times at the selected sterilization temperature, and then keep warm to check the spoilage rate.

Usually, the sterilization test is carried out by inoculating spoilage bacteria with strong heat resistance into a small number of cans to confirm the safety of the sterilization conditions. The truthful tank inoculation sterilization test result is very close to the theoretical calculation result, which has a more reliable guarantee and a high degree of confidence in the rationality and safety of the prescribed sterilization conditions.

1. Microorganisms for testing

(1) Low-acid food: Clostridium sporogenses PA3679 spores

(2) Acidic food below pH 3.7: Clostridium pasteurianum

or Bacillus coagulans spores

(3) Highly acidic foods: lactic acid bacteria, yeast

2. Method of inoculation

(1) Convective heat transfer products

can be inoculated anywhere in the tank.

(2) Conductive heat transfer products

Inoculate as much as possible in cold spots.

4, test group

According to the theoretical calculation of sterilization conditions, it is divided into at least 5 groups according to the length of sterilization time. Group 1 is the shortest sterilization time and the sample corruption rate reaches 100%; Group 1 is the longest sterilization time, and the corruption rate is expected to reach 0% ; The sterilization time of the other three groups will have different spoilage rates. Usually the sterilization time is between 30 and 100, and one group is made every 5 minutes. Ideally, the F value decreases according to the logarithm as the temperature increases. The F value can be grouped according to 0.5, 1.0, 2.0, 4.0, 6.0 to determine different heating times. Each test should be controlled to 5 groups, otherwise there are too many cans and the residence time before and after sealing is too long, which will affect the test results. Therefore, the test is required to be completed in one day and use the same material.

There should also be 3 to 5 groups of canned food in the control group, so as to check the heat resistance of natural contaminated microorganisms, and to check whether the double curling is good, the net weight in the can, the drained weight, and the degree of headspace. 6-12 cans will also be used for measuring cold spot temperature.

5. Test record

During the test, the following contents must be measured and recorded.

A. The name and number of the inoculated microorganism;

B. The amount of inoculated bacteria, the number of inoculated bacteria and the method of inoculation;

C. Operation time (such as pretreatment time, canning time, exhaust, residence time before sealing, etc.);

D. blanching temperature and time;

E. Filling temperature;

F. Filling weight;

G. Content viscosity (if it is an important factor);

H. Head clearance;

I. Concentration of brine or soup;

J. Hot exhaust temperature and time;

K. Sealing and steam injection conditions;

L. Vacuum degree (refers to vacuum sealing);

M. The temperature of the contents during sealing;

N. Initial temperature of the can before sterilization;

O. Sterilization heating time;

P. The temperature and time of each stage in the sterilization process;

Q. The indication value of the instrument on the sterilization pot (pressure gauge, mercury thermometer, temperature recorder);

R. Cooling conditions.

(3) Heat preservation and storage test

After the inoculation of the solid tank test, the sample should be subjected to a heat preservation test at a constant temperature. The culture temperature varies according to the test bacteria:

Mold: 21.1～26.7℃

mesophilic bacteria and yeast: 26.7～32.2℃

Bacillus coagulans: 35.0～43.2℃

Thermophilic bacteria: 50.0～57.2℃

Insulation test samples should be observed every day for any changes in the appearance of the container. When the cans expand, they should be taken out and stored in the refrigerator.

After the heat preservation test is completed, the cans are left to cool overnight at room temperature, and then the appearance of the container, whether the bottom cover of the can is expanded, and whether the vacuum is low, and then all the test cans are opened for inspection to observe their shape, color, pH value and viscosity. Consistency, etc., and record the results one by one. To inoculate the botulinum sample to do a toxicity test, it is also possible that some cans produce poison but not gas.

When the appearance and contents of the container are found to be different from the symptoms that the original inoculated test bacteria should have, it may be caused by leaking tank pollution or natural contamination with more heat-resistant microorganisms, which requires the separation of spoilage bacteria test.

(4) Real can test on production line

If the results of the inoculation solid can test and the heat preservation test are normal, the canned food can be heated and sterilized under normal conditions, and then it can enter the solid can test of the production line for final verification. The sample size is at least 100 cans. The following contents must be measured and recorded during the test:

A. Heating temperature and time;

B. Filling temperature;

C. The amount of cans (solids, soup volume);

D. Consistency (curry, thick soup products);

E. Head clearance;

F. The temperature of salt water or soup;

G. Concentration of brine or soup;

H. The pH value of food;

I. Water activity of food;

J. Steam injection conditions of the sealing machine;

K. Vacuum degree (refers to can sealing machine);

L. The temperature of the food when the can is sealed;

M. The average number of microorganisms per gram (or per milliliter) of the food before heat sterilization and its fluctuation value, the sampling frequency is 5-10 times. Highly acidic foods below pH 3.7 are tested for lactic acid bacteria and yeast; acidic foods with pH 3.7 to 5.0 are tested for the number of spores of mesophilic aerobes (if possible, the number of spores of mesophilic anaerobes should also be tested); pH5. Test the number of spores of mesophilic aerobes and thermophilic aerobes (if possible, the number of spores of mesophilic anaerobes should also be tested) for low-acid foods above 0, which is the lowest limit for ensuring sterilization conditions Very necessary.

N. The initial temperature of the can before sterilization;

O. Sterilization heating time;

P. Sterilization temperature and time;

Q. The indication value of the pressure gauge, mercury thermometer and temperature recorder on the sterilization pot;

R. The uniformity of temperature distribution in the sterilization pot;

S. The record of the measured point temperature (cold point temperature) and its F value during canned sterilization;

T. Canned food tightness inspection and its results.

The solid tank samples of the production line are also subject to thermal insulation test, and it is hoped that the thermal insulation will be kept for 3-6 months. After the thermal insulation sample is opened, the test results show that the contents are all normal, and the sterilization conditions can be used in production. If there are spoilage bacteria, the separation test of causative bacteria must be carried out.

Dry heat sterilization:

Microwave sterilization by burning or dry hot air is called dry heat sterilization. Although the penetration power of dry main hot air is not as strong as that of humid hot steam, it is convenient to use and suitable for the sterilization of glassware and porcelain, so it is widely used in laboratories and production practices.

The mechanism of sterilization

Dry heat refers to high heat with a relative humidity below 20%. Dry heat sterilization is conducted by air, and the heat transfer effect is slow. Generally, propagules can be killed in a dry heat of 80-100°C for 1 hour, and spores can be killed after 2 hours at 160-170°C.

Dry heat sterilization is one of the methods of using high temperature to kill microorganisms. Usually high temperature is used, such as direct flame heating, or hot air treatment at 160-180℃.

The most important components of microbes are protein, nucleic acid, etc. When high temperature is encountered, it will cause irreversible denaturation or coagulation of protein and nucleic acid, causing cells to lose their physiological functions and stop growth and development until they die. In addition, high temperature can destroy other components of the cell, or cause the fat membrane of the cell to be dissolved by heat to form a huge hole, causing the cell content to leak and cause death, thereby achieving the effect of high temperature sterilization.

flame sterilization

(一) concept

The flame sterilization method is a method of sterilization by high-temperature flame burning

(2) Application areas and characteristics.

1. Inoculation operation:

Heat-resistant inoculation loops, inoculation shovel, inoculation spoons, inoculation needles, etc., can be thoroughly sterilized by flame burning. Test tube mouth and glass bottle mouth, through the flame several times, the temperature can reach more than 200 ℃, all microorganisms and spores, All can be killed to achieve sterility.

2, canning industry

Flame sterilization in the canning industry uses flames to directly heat the cans, which is a high-temperature short-term sterilization under normal pressure.

During 　　 sterilization, the cans are preheated and rolled over a high-temperature flame (temperature above 1300℃), reaching high temperature in a short period of time, maintaining a short period of time, and then cooling by water spray.

The food in the tank does not need soup as a convection heat transfer medium, and the content of the solid content is high.

Due to the high pressure inside the tank during sterilization, it is generally only used for small metal tanks. The sterilization temperature of this method is more difficult to control (generally determined by measuring the heat radiated by the can after adding.)

hot air sterilization

(一) concept

Hot air sterilization is a method of sterilization using heated high-temperature air.

(2) Features

1. This sterilization method is suitable for glassware, porcelain, stainless steel ware, gelatin sponge, liquid paraffin, various Powders, ointments, etc. are not suitable for the sterilization of liquid materials.

2. Due to the poor penetration of dry hot air and the fact that microbial protein is not easy to coagulate and deteriorate under dry conditions, the dry heat sterilization temperature is generally required to be controlled at 160°C and maintained for 2 hours.

3. Dry heat oven is a common instrument for dry heat sterilization. It is heated and adjusted by electric heating wire. The air heated by electricity is continuously convective in a certain space, and the hot air that produces a uniform effect directly penetrates the object. In general, propagules can be killed in a dry heat of 80-100°C for 1 hour, and spores and viruses can be killed in 2 hours at 160-170°C.

(3) Operation precautions

1. The dry heat sterilization temperature exceeds 170℃, and the paper, cotton and cloth used for packaging sterilization products will be scorched by the hot air, and there is even a danger of fire.

2. Operate the dry heat sterilization box. After sterilization, wait until the temperature in the box drops below 50-40℃ to open the cabinet door to prevent explosion.

Main equipment and installations

(1) Equipment composition

The main equipment for dry heat sterilization includes dry heat sterilization cabinet and tunnel sterilization system. Dry heat sterilization equipment generally consists of the following important parts:

1, heater

It is the main component of dry heat sterilization equipment, which has a great influence on the quality of sterilization.

2, high efficiency filter

is used to remove the dust and substances generated in the internal air circulation system to prevent the pollution of exhaust air backflow.

3, buffer plate, damper, air regulator or air baffle

Buffer plate or air baffle plate is used to control the air flow of the dry heat sterilizer; the air flow regulator is used to control the positive pressure in the sterilizer chamber.

4, fan

has a great influence on the air circulation in the dry heat sterilizer, ensuring the good condition of the hot air circulation.

5. Conveyor belt (only applicable to continuous method)

The speed of the conveyor belt is very important in the continuous conveying dry heat sterilization system. Its conveying speed determines the heat received when the material passes through the sterilizer and the corresponding sterilization effect. 6. Run interlocking control system

Prevent the sterilized items from passing through the sterilizer when the temperature is lower than the sterilization temperature.

7, temperature controller and recorder

Record the temperature readings of the temperature detection and sensor system accurately and clearly.

Key factors for process equipment control:

(1) Application scope of dry heat sterilization

can be used to sterilize items that can withstand higher temperatures, but are not suitable for steam penetration, or that are easily damaged by damp heat.

(2) Evaluation of the effect of sterilization process

1, the fatality rate F0 value:

Similar to the F0 value used in the verification of the humid heat sterilization system, it is the equivalent time when the time and humidity conditions are converted into 170 ℃, and the Z value is set to 20 ℃, which is the FH value. The 1993 version of BP stipulates that the dry heat sterilization system only uses sterilization as the final purpose and must ensure that its minimum FH value is greater than 170°C for 60 minutes.

2. Biological indicator--microbial survival rate

For systems that are sterilized by dry heat survival probability method, the verification result should be able to prove that the sterilization process ensures that the killing effect of heat-resistant microorganisms reaches the recognized low survival probability, and the general probability of not being killed is 10-6.

For the verification results of the sterilization system using the dry heat over-killing method, it should be proved that the sterilization process guarantees that the microorganisms with high tolerance to dry heat produce a decline of greater than 12 log, and the survival probability of microorganisms is less than 10-12. .

(3) Control of sterilization equipment

1, heater

Heater failure is one of the main reasons that cause the sterilization effect of dry heat sterilization equipment to decline, which is mainly manifested in the decrease of the heating rate; affects the heat distribution; and produces dust substances. The cause of heater failure is mainly due to the long-term use of the heater or the poor quality of air passing through the heater. Therefore, it is generally necessary to configure a current monitor in the heating system of the sterilizer to find its fault in time.

2, high efficiency filter

must meet the air volume requirements of the dry heat sterilization process and be able to withstand the corresponding air pressure.

3, buffer plate or air baffle

Used to control the air flow of the dry heat sterilizer, mostly installed near the inlet or exhaust duct or heater

4, air flow regulator

For positive pressure control, it can be installed near the high efficiency filter in the exhaust system to prevent backflow air pollution. The positive pressure can be controlled by controlling the exhaust air volume, or the airflow regulator can be used to control the air intake and exhaust air volume to maintain the positive pressure .

Under normal circumstances, the pressure in the dry heat sterilizer chamber is slightly higher than the adjacent non-sterile zone and slightly lower than the adjacent sterile zone.

5. Fan

The air volume of the fan should be measurable and adjustable. If necessary, the supplier can be required to add this requirement to its equipment standard, because the measured value of the fan air volume can provide a basis for checking the status of the fan during the use of the equipment.

6, conveyor belt (only applicable to continuous method)

It is necessary to keep records of the conveying speed of each sterilization process in the production process. At the same time, the SOP of the dry heat sterilizer should also clearly specify the operating speed range of various sterilization process conveyor belts. This operating speed range should be verified and determined.

7. Operation interlocking control system

The interlocking control system in the dry heat sterilizer is equipped with: door interlocking control system; pressure sensor; interlocking control device for temperature sensing, control, and stop conveyor belt operation, etc., to ensure that the temperature is lower than the design requirements in any case Bacteria items pass through the sterilizer at a temperature lower than the sterilization temperature.

8. Temperature controller and recorder

In the dry heat sterilization system, the temperature detection, sensing, control, and recording system is the basis of the entire sterilization process control. The control system must ensure that the sterilization temperature in the sterilizer chamber can be maintained at the set sterilization temperature Within the scope, its recording system must record the temperature detection and temperature readings of the sensor system accurately and clearly.

The concept and nature of microwave:

(一) concept

Microwave refers to electromagnetic waves with a wavelength of about 1m to 10mm, which are often divided into four bands: meter wave, centimeter wave, millimeter wave and submillimeter wave.

The frequency of microwave (300MHz～300GHz) is between radio frequency (ultra-short wave) and far infrared frequency (low frequency end). Because of its high frequency, it is also called UHF electromagnetic wave in some occasions.

(二) Nature

1, fluctuation characteristics

2, straight line propagation

3, microwave energy has spatial distribution properties

4. Microwave energy is transmitted in the form of mutual induction of alternating electric and magnetic fields.

The scope and characteristics of microwave applications

(1) Application category

At present, only 915MHz (896MHz in the US) and 2450MHz are widely used in the industry.

(2) Features

1. High heating efficiency, energy saving

2. Fast heating speed, easy to control

3, different food ingredients have different selective absorption of microwave energy

4, water leveling effect

5, help to ensure product quality

6. ​​Microwave heating equipment is small in size and occupies a small plant area

Development Overview

The use of microwave heating in industry began in the late 1970s. Due to the increase in energy costs, people are looking for more effective industrial heating and drying methods. As a heat source, microwave has the characteristics of fast heating speed and high energy utilization. Therefore, microwave heating technology and microwave oven applications have developed rapidly.

Microwave heating principle

Food microwave processing mainly uses the thermal effect of microwaves. Water, protein, fat, carbohydrates, etc. in food are all dielectrics. The dielectric material absorbs microwaves to increase the temperature of the medium. This process is called dielectric heating.

(1) ion polarization

The ions in the solution are polarized by the electric field. The ions carry electric charges to obtain kinetic energy from the electric field, and collide with each other, which can convert kinetic energy into heat.

(two) dipole turning

In some dielectrics, the positive and negative charge centers of the molecules do not coincide, that is, the molecules have a dipole moment. Such molecules are called dipolar molecules (polar molecules). When polar molecules are subjected to an external electric field, dipole molecules will produce torque. In the high-frequency electric field, the polar molecules have to perform hundreds of millions of commutation "pole-changing" movements within one second, causing strong vibration between the molecules, causing friction and heating, increasing the temperature of the material, and achieving the purpose of heating.

The effect of microwave on microorganisms

(1) Microwave heating effect

1. The rapid temperature rise of microorganisms leads to denaturation of bacterial proteins and death of living organisms;

2. The life activities of microorganisms are severely disturbed and cannot reproduce;

3, cause the cell membrane to rupture, cause the physiologically active substance to undergo denaturation, and lose its physiological function;

4. Destroy the survival and reproduction conditions of microorganisms and cause their death.

(2) Microwave non-thermal effect

1, photochemical reaction

2, field effect

3, electromagnetic resonance effect

4. Affect the content of genetic material DNA

Microwave sterilization related equipment and devices

(1) Microwave energy generating device

1, electric vacuum device

(1) Magnetron

(2) Multi-chamber klystron

(3) Microwave triode and tetrode

(4) Traveling wave tube and orthogonal field device

2, semiconductor devices

(2) Microwave heating equipment

1. The composition of the microwave heating system

2. Types and structural characteristics of microwave heaters

(1) Type

① Standing wave field resonant cavity heater (box type)

② Traveling wave field waveguide heater (waveguide type)

③ Radiant heater

④ Slow wave heater

Electric kill concept and characteristics

(1) Basic concepts

Electrothermal sterilization is also known as "ohmic sterilization". It uses electrodes to pass current through the object. Due to impedance loss, dielectric loss, etc., the electrical energy is finally converted into heat, so that heat is generated inside the food to achieve the purpose of sterilization.

(2) Technical Features

The frequency of using alternating current is 50-60Hz. It uses electrodes to direct current into the food, and generates heat from the dielectric properties of the food itself to achieve the purpose of sterilization.

1. Heating is self-conducted through the product

2, AC is applied to the product

3, the depth of electric penetration is unlimited

4, there is no big thermal gradient in the product

5. The heating is controlled by the conductivity of the product and the remaining heating time

6, heating to kill microorganisms

(three) advantages and disadvantages

1, advantages

(1) The diameter of disinfection particles is more than 1 inch

(2) Minimal mechanical damage to particles

(3) Unified heating of particles inside the product

(4) Can avoid excessive heat treatment of materials

(5) Can handle materials containing more than 80% solids

(6) Minimal equipment pollution

(7) Reduce the loss of product nutrition color and flavor

2, disadvantages

(1) The process relies on the conductivity of the product to heat the product

(2) Cannot be used to treat fat, oil, alcohol, bone or ice

(3) The product formula must be carefully controlled to control the resistance

(4) The design of production equipment must be specific to the product

(5) Some foods may require thermal or chemical reprocessing in order to change their conductivity

(6) The product flow rate and temperature must be controlled to ensure that microorganisms are killed

Processing category

(1) Processing material characteristics

1. The applicability of electric heating is determined by the conductivity of the food material

2. Most foods that can be transported by pumps, dissolved in salt ions and have a water content of more than 30%, can be sterilized by resistance heating

3, suitable for the sterilization treatment of food materials with high particle density and high viscosity

4. Most suitable for aseptic packaging products

5. This technology is not applicable to non-ionized foods such as some fats, sugars, oils, treated water without added salt, etc.

(2) Processed varieties

1, Chinese prepared food

(1) Congee

(2) Soup

2, fruit and vegetable products

(1) Tomato pulp

(2) pineapple pieces

(3) strawberry jam

(4) diced mango/diced papaya

(5) tropical fruit block

(6) Peach/Apricot/Pear/Apple and other pulp products

(7) Block products such as potato/carrot/mushroom

3, livestock and poultry products

(1) Beef stew

(2) Braised chicken

Comparison with conventional heat sterilization methods

Heat sterilization of fluid food containing particles

(1) Conventional heat sterilization

1, heat transfer method

Using a heat exchanger for indirect heat exchange, the process rate depends on the heat exchange conditions of conduction, convection or radiation.

In the case of partition wall heat transfer, heat is first transferred from the heating medium (such as water vapor) to the liquid in the food material through the partition wall, and then transferred to the solid particles by the convection and conduction between the liquid and the solid particles, and finally the internal conduction transfer of the solid particles. Heat to make all materials reach the required sterilization temperature.

The heat transfer rate is slow and the heating is not balanced.

2, heating effect

To make the inside of the solid particles reach the sterilization temperature, the surrounding liquid part must be overheated, which will inevitably lead to the soft texture and shape change of the food containing the particles after sterilization, which will affect the product quality.

(二) Electric sterilization

1, heat transfer method

Apply current to the fluid and particles at the same time. If the conductivity of the two is similar, the two will generate heat rapidly at the same time and the heating degree is quite uniform.

The heating rate of particles is much higher than that of conventional methods.

2, heating effect

The purpose product does not experience a large temperature gradient during heating and the liquid and the particles are heated at the same time, so the processing time is short, the product quality is high, and the product can maintain the good particle shape after high temperature treatment.

The heating surface does not burn, the product is not allowed to be stirred during heating, and the liquid carrier does not need to be overheated to heat the particles and the particles are evenly heated.

The mechanism of electrothermal sterilization

Electric heat sterilization can kill E. coli, yeast and bacillus in liquid food. The main sterilization mechanism is:

1. When the current is used to pass the food, the polar molecules in the food continuously rotate and rub under the high-frequency change of the electrode polarity to generate heat, which can kill the living bacteria;

2. The bacterial cells between the two electrified electrodes are sterilized due to the destruction of the bacterial cell membrane due to the action of the applied electric field.

Factors affecting the sterilization effect

1. Product composition

2. The electrical resistance of the product and its change with temperature

3, product flow rate

4, product temperature

5, heating cycle

related equipment and devices

(一) electric heater

(二) Small electric sterilization production line

The key factor of process control

1. Determine and control the specific electrical resistance of the product and its change with temperature

2,The flow rate of the product is the key to the heating of the product

3. Heat production rate and heating cycle in ohm heater are the main factors

4. The operating procedures should be established by people with knowledge and experience

5. Aspects that should be strictly controlled: product formulation, flow rate, product temperature in the heater, and other key control points

non-thermal sterilization

Chemical sterilization technology

(1) Basic concepts

mainly refers to adding antibacterial agents and preservatives to food to achieve the purpose of antibacterial or sterilization.

(2) Process characteristics

1, advantages

(1) Easy to operate and control

(2) Good sterilization effect

(3) Lower cost

2, disadvantages

(1) In use, it is easily affected by factors such as moisture, temperature, pH value and body environment, and the effect varies greatly

(2) Repeated use of chemical reagents remaining in food may cause bacteria to produce antibodies

(3) Residual chemical reagents will affect the natural flavor and texture of food

Biological sterilization

(1) Basic concepts

Biological fungicides refer to substances extracted from the metabolites of plants, animals and microorganisms. Biological sterilization achieves the purpose of antibacterial or sterilization through the effect of biological agents on the microorganisms in food materials or products.

(2) Process characteristics

1. It has strong antibacterial and bactericidal effects

2, many prevention and treatment sites

3, high efficiency, low toxicity, no residue

4, long-lasting drug effect, difficult to produce resistance

5. Use safety

The sterilization principle of chemical agents

1. Change the permeability of cell membrane

Surface-active agents, phenols and alcohols can cause disorder of the cytoplasmic membrane structure and interfere with its normal function, causing small molecular metabolites to overflow outside the cell, affecting cell transfer activity and energy metabolism. Even cause cell rupture.

2, lead to denaturation or coagulation of microbial protein

Acid, alkali, alcohol and other organic solvents can change the configuration of the protein and mess up the folding method of the polypeptide chain, causing protein denaturation. Such as ethanol, most heavy metal salts, oxidants, aldehydes, dyes and acids and bases.

3. Factors that change the functional groups of proteins and nucleic acids

"It acts on the functional groups (such as SH groups) of bacterial intracellular enzymes to change or inhibit its activity. For example, certain oxidants and heavy metal salts can bind to the -SH group of bacteria and make them inactive.

The sterilization principle of biological agents

1, inhibit the synthesis of bacterial cell wall

2. Affect the permeability of bacterial cell membrane

3, inhibit the synthesis of bacterial protein

4. Inhibit bacterial nucleic acid synthesis

Types of commonly used chemical fungicides

1, halogen fungicides

2, oxidant fungicides

3. Surfactant fungicide

4, heterocyclic gas bactericide

5. Alcohol fungicides

6, chlorhexidine fungicide

Factors affecting the sterilization effect

1. Cleanliness of materials

2. Concentration and nature of fungicides

3, the action time of the material and the fungicide

4, temperature, humidity, pH value

5. Types, quantity and living conditions of microorganisms

6, environmental factors

7, chemical antagonist

Ideal fungicide characteristics

1, has a broad germicidal effect

2, not affected by organic matter, good penetration

3, non-corrosive, toxic or irritant, no damage to utensils

4, fast action, and stable properties

5. Have continuous antibacterial effect

6. Reasonable price

microbial inhibitor

1, concept

is a new type of antibacterial technology developed based on the production of antibiotics in response to the invasion of pathogens by animals.

2, mechanism of action

MBA is a special factor that can inhibit the formation of microorganisms on the surface of the body and can be adsorbed to body tissues, and it can also compete with the tissue binding sites in biological epithelial tissues. Through this dual action mode, microorganisms on the body surface are rejected.

3, types and uses

(1) Nisin

can be used for canned food, vegetable protein food, milk and meat products

(2) Natamycin

It can be used to prevent mildew on cheese, meat products, broth, Western-style ham, Cantonese-style mooncakes, pastry surfaces, fruit juice puree surfaces, moldy foods, processed utensils, etc.

Antibiotic enzyme sterilization

1, concept

The main active ingredient of 　　 antimicrobial enzymes is lysozyme (Lz), which can inhibit Gram-positive bacteria.

2, mechanism of action

destroy the cell membrane of bacteria.

3, use

Dairy products, meat products, fruit and vegetable products

Plant natural antibiotic sterilization

1, plant antitoxin

2, phenols

3, organic acids

4, essential oils

Ultraviolet sterilization technology concept

Ultraviolet sterilization technology uses ultraviolet rays to irradiate substances to change the molecular structure of the microbial inner nuclear protein on the surface of the object and cause death.

Overview of the development of ultraviolet radiation

Due to the poor penetration of ultraviolet light, ultraviolet radiation is generally used for the surface of food factories, equipment, packaging materials and water sterilization. In addition, ultraviolet radiation can also be combined with other strong oxidants such as ozone, hydrogen peroxide and other treatments for sterilization. In recent years, the use of ultraviolet rays to sterilize transparent liquids has been developed, and the application of ultraviolet rays in fruit and vegetable juices has also attracted attention.

In November 2000, the U.S. FDA approved California Day-Fresh Foods and Salcor's application for the use of ultraviolet light for the sterilization of fruit and vegetable juices, and revised the 21CFR179 food additive regulations to allow ultraviolet radiation to be used for the disinfection of fruit and vegetable juice beverage products, and stipulate ultraviolet light. The low-pressure mercury lamp is used for the generation of light, 90% of the light wavelength is 2537nm, and the Reynolds number of turbulence is not less than 2200.

Ultraviolet characteristics

(一) Wavelength

1, long wave band (3200～4000nm)

2, medium band (2750～3200nm)

3, short wave band (1800～2750nm)

Among them, ultraviolet rays in the range of 240-280nm have strong bactericidal power, and the strongest wavelength is 250-265nm, and 253.7nm is mostly used as the ultraviolet bactericidal wavelength.

(2) Nature of Communication

1, ultraviolet rays spread in a straight line

2, the intensity of ultraviolet light decreases in proportion to the square of the distance

3, can be reflected by different surfaces, weak penetrating power

Ultraviolet radiation sterilization principle

When microorganisms are irradiated by ultraviolet rays, some amino acids and nucleic acids of their cells absorb ultraviolet rays and produce photochemical effects, which cause chemical changes in cell components, especially nucleic acids, protoplasmic proteins, and esters, and denature the cytoplasm. At the same time, the air is exposed to ultraviolet rays. A small amount of ozone, together with sterilization, leads to the death of microorganisms.

Ultraviolet sterilization equipment and devices

1, ultraviolet germicidal lamp (Beijing Dafu Medical Products Co., Ltd., Beijing Yabei Modern Instrument and Equipment Technology Co., Ltd.)

2, Ultraviolet high-pressure mercury lamp (Beijing Yaming Electric Light Source Development Company, China Xiamen Instrument Company Management Department)

3. Ultraviolet intensity detector (Beijing Dafu Medical Products Co., Ltd.)

4. Ultraviolet reflectometer (Beijing State-owned Science Instrument Factory)

5. Ultraviolet Detector (Beijing State-owned Science Instrument Factory)

6, single door ultraviolet disinfection box (Beijing Lida Shitong Trading Co., Ltd.)

7, double-door ultraviolet disinfection box (Beijing Lida Shitong Trading Co., Ltd.)

8. Ultraviolet sterilizer (Beijing Dongsheng Glass Light Source Factory)

9. Household ultraviolet water purifier (Beijing Dongsheng Glass Light Source Factory)

10. Ultraviolet sterilization vehicle (Beijing Dongsheng Glass Light Source Factory)

11. Ultraviolet disinfection monitor (China North Industries Corporation)

Ultraviolet sterilization process characteristics

1, advantages

(1) Easy to operate

(2) The system price is lower than other sterilization systems

2, disadvantages

(1) Can only be used to sterilize the surface system of transparent liquid film

(2) Ultraviolet rays must penetrate into the product, contact the microorganisms to be killed, and impart sufficient energy

UV sterilization operation control

1. The necessary dose of ultraviolet light to inactivate microorganisms is determined by time and intensity

2. Continuous monitoring of natural ultraviolet light, flow rate, turbidity, product properties and lamp output is required

3. The bactericidal power of ultraviolet rays decreases with the increase of use time. Generally, the ultraviolet lamp should be replaced when the use time reaches 70% of the rated time to ensure the sterilization effect.

4. The bactericidal effect of ultraviolet rays varies with different bacterial species, and the radiation dose for fungicides is 40-50 times larger than that for bactericidal.

5. Ultraviolet radiation is usually designed based on a relative humidity of 60%. When the indoor humidity increases, the exposure should increase accordingly

6. ​​The effect of ultraviolet sterilization is related to the length of time of irradiation, which requires verification to determine the irradiation time

7. The installation form and height of the UV lamp should be determined according to the actual situation and refer to the instructions for use

Ultraviolet sterilization application range

1. Air and surface disinfection

2, pasteurization of transparent liquid

UV sterilization factors

1. Product permeability

2. The geometry and power of the reactor

3, the wavelength of ultraviolet

4, the flow state of the product

5, UV irradiation path length

Ultra-high static pressure sterilization technology

concept

Ultra-high static pressure (UHP or HHP) processing technology for food refers to the process of placing the food sealed in an elastic container in a pressure system with water or other liquids as the pressure transmission medium, and subjecting it to a pressure above 100 MPa to achieve sterilization and destruction. Enzymes and improve the functional properties of food.

Ultra-high pressure treatment is usually carried out at room temperature or lower temperature. Under a certain high pressure, food protein is denatured, starch gelatinized, enzymes are inactivated, life stops, and bacteria and other microorganisms are killed.

Overview of the development of ultra-high pressure sterilization technology

At the end of the 19th century-Tamman used a pressure of 300 MPa to measure the changes in the solid and liquid phases, opening the door to high-pressure technology, and was honored as the "mother of ultra-high pressure"; Bridgman continued his research in this area and achieved extraordinary achievements. Nobel Prize in Physics, and is honored as the "Father of Ultra High Pressure". The research on the application of high static pressure in food preservation was first proposed by Hite (1899), but his work did not receive much attention. In the following decades, most of the research reports on the effects of high pressure on intact cells focused on microorganisms under natural high pressure conditions.

From 1895 to 1965, a total of 29 kinds of microorganisms were selected as the target bacteria for UHP sterilization. It was not until the mid to late 1980s that the application of high pressure processing technology in food began to attract attention. In 1986, Professor Lin Limaru from Kyoto University in Japan took the lead in publishing a report on the treatment of food with high static pressure, which attracted the attention of the Japanese food industry and academia. In April 1990, Meijiya's first high pressure jam (High Pressure Jam) produced by using high pressure instead of heat sterilization was put on the market. The products can reach a certain shelf life without heat sterilization, and they are doubled by the color, flavor and taste of fresh fruits. Favored by consumers. Currently, Japan's research in this field is still a world leader. A complete set of ultra-high pressure processing equipment is already on the market.

Since 1986, Japan has held academic seminars on high-voltage technology applications every year. Europe also held its first meeting on the application of high-pressure technology to the food industry in France in October 1992, and the European Community immediately loaned money to support a multi-country joint research project for the development of high-pressure food. In a special report, IFT, the highest academic authority on American food, listed the development of high-pressure food as the main research project of American food engineering in the 21st century. my country's national food industry development plan also included high pressure sterilization as one of the sixteen key development technologies in the 1990s.

The effect of stress on microorganisms

Under high pressure, proteins and enzymes will be denatured, and the nuclear membrane of microorganisms will be compressed into many small fragments and protoplasm will become paste together. This irreversible change can cause the death of microorganisms.

Other factors affecting the resistance of microorganisms to stress

1、 Types of microorganisms

2, cell morphology

3. Types and characteristics of food media

4, pressure temperature

5, pressure time

6, the pressure

7, pressure mode

8. The synergy of pressure and other sterilization technologies

Kinetics of microbial inactivation under high pressure

The death of microorganisms follows first-order reaction kinetics

Press Equipment Manufacturer

1, USA--Flow International Corp.

2, France--Alstom Company

3, Japan--Kobelco (Kobe Steel Ltd.)

4, Netherlands--Stork Food & Dairy Systems B. V.

5. Sweden--ABB

1, ultra-high pressure sterilization machine

Equipment Characteristics

Ultra-high pressure sterilization machine's sterilization principle is to use ultra-high pressure to destroy the tissue of mold and bacteria to maintain the freshness of food. There is no such thing as heating, adding preservatives, and other traditional sterilization methods that cause food nutrition and flavor loss.

This device is batch type, and the pressurizing tank adopts a continuous method, which is a high-efficiency mass production method.

Process control of ultra-high static pressure sterilization technology

Process characteristics

(1) Advantages

1. The food is kept fresh without heating during processing

2, the processing process can be applied to the final package

3, the liquid food process can be used as a part of the aseptic process

4. Enzyme activity can be stopped

(2) Disadvantages

1. High pressure causes protein gelation, and enzyme activity may increase due to cell wall rupture

2, can cause protein gel, annotation and swelling

3, cause changes in food tissue

4, the initial installation cost of the equipment is high

5. Bacterial spores, molds and yeasts may require different high pressures to be eliminated for a long time

Operation control

1. Ultra-high pressure processing requires very special equipment, such as orange juice may be batch processed in a pressure chamber, and then aseptically filled in pre-sterilized packaging.

2, ultra-high pressure processing must Consider the type of microorganisms, product characteristics, ideal process (pasteurization or commercial disinfection), and product sales methods.

3. Ultra-high pressure treatment is very effective for growing bacteria, yeasts and molds, but the spores will not be inactivated by high pressure, and additional heating or other actions are required to achieve a high level of killing.

Application of ultra-high static pressure sterilization technology

Technical advantages

1. It can achieve sterilization and enzyme-killing effect at room temperature or lower temperature. Compared with traditional heat treatment, it reduces the loss or deterioration of food nutrients and color, aroma and taste caused by high heat treatment.

2. Because the pressure transmission speed is fast, uniform, and there is no pressure gradient, the ultra-high pressure processing is not affected by the size and shape of the food, making the ultra-high pressure processing relatively simple

3. It consumes less energy, and only needs to use hydraulic high-pressure pump to increase the pressure in the boosting stage, while the constant pressure and depressurization stages do not need to input energy

Application area

Natural fruit juice, jam, beverage, soy milk, yogurt, livestock and poultry meat products, aquatic products, etc.

Pulsed electric field (PEF) sterilization technology

concept

Pulsed electric field sterilization is to place food in an instant high-voltage electric field generated between two electrodes. Because the high-voltage electric pulse can destroy the cell membrane of bacteria, change its permeability, and kill the cells.

Development Overview

As early as 1879, Cohn and Mendelsohn discovered that an electric field in a solution can kill bacteria. In recent years, with the development of electronic processing technology, in-depth research on the sterilization effect of pulsed electric field technology has been gradually carried out. At present, it is transitioning from pilot experiment to commercial experiment. The research is mainly conducted at Ohio State University. Pulsed electric field technology can sterilize liquid materials at a temperature below 40°C. In the case of continuous operation, it can kill E. coli, brewer's yeast and Staphylococcus aureus.

High-intensity pulsed electronic fields that kill microorganisms in food have been studied in many countries around the world. One of the leading industrial companies in the United States, Pure Pulse Technology, such as San Diego, California, has submitted information to the FDA to support their use of PEF for microbiological treatment of liquids and canned foods. After reviewing this information, the FDA decided that the food additive regulations do not require PEF, as long as they comply with the requirements of good operating practices and use high-intensity pulsed electronic fields to process any food without any quality changes.

Hypothesis about the mechanism of sterilization

1. Cell membrane perforation effect

2, electromagnetic mechanism model

3, viscoelastic polarity formation model

4, electrolysis product effect

5, O3 effect

The basic principle of sterilization

1. The role of the field

The pulsed electric field generates a magnetic field. The alternating action of the pulsed electric field and the pulsed magnetic field increases the permeability of the cell membrane, intensifies the oscillation, and weakens the membrane strength. As a result, the membrane is destroyed, the material in the membrane is easy to flow out, and the material outside the membrane is easy to penetrate, and the protective effect of the cell membrane is weakened Even disappear.

2, ionization

The anions and cations produced by the ionization of the material near the electrode interact with the living substances in the membrane, thus blocking the normal biochemical reactions and metabolic processes in the membrane; at the same time, the ionization of the liquid medium produces a strong oxidation of O3, which can interact with the substances in the cells. A series of reactions.

Through the combination of the above two actions, it kills the bacteria.

Pulse electric field generation method

1. Using the principle of LC oscillation circuit

First use a high-voltage power supply to charge a group of capacitors, connect the capacitors with an inductance coil and the electrodes of the processing chamber, and the high-frequency exponential pulse decay wave generated when the capacitors are discharged is applied to the two electrodes to form a high-voltage pulse electric field.

2. Use a specific high-frequency and high-voltage transformer

Get a continuous high-voltage pulse electric field.

equipment

Process characteristics

(1) Advantages

1. Eliminate a large number of pathogenic bacteria and spoilage organisms

2, there is only a slight temperature increase in the product

3. Compared with heat treatment, the price is lower

4. There is no change in the product, no loss of vitamins and enzymes

(2) Disadvantages

1. Need high dose and long time for spores

2, can only be used for liquid or filling

3, can only be used for shelf-stable acid food and refrigerator food

4, each specific product design process must be

Factors affecting the sterilization effect

1, food characteristics

2, electron field peak intensity (KV/cm)

3, pulse period (microseconds)

4, the number of pulses

5. Initial temperature and maximum processing temperature

6. ​​Related microorganism types and microorganism inoculation

Process parameters

1. The intensity of the high-voltage pulsed electric field for sterilization is generally 15～100kV/cm

2, the pulse frequency is 1～100kHz

3, the discharge frequency is 1～20kHz

Application of pulsed electric field sterilization technology

Technical characteristics

1. The sterilization time is short, and the energy consumption in the treatment process is much less than the heat treatment method

2. As it is carried out at normal temperature and pressure, the processed food has little change in physical properties, chemical properties, and nutritional components compared with fresh food, and there is no noticeable difference in flavor and taste.

3. Obvious sterilization effect (N/No<10-9), which can meet commercial sterility requirements

4, the sterilization time is very short, less than 1min, usually tens of microseconds can be completed

Vibration magnetic sterilization (vibration magnetic field sterilization technology)

basic concepts

Magnetic sterilization adopts 6000 magnetic strength. The food is placed between the N pole and the S pole. After continuous swing, without heating, 100% sterilization effect can be achieved without any influence on the ingredients and flavor of the food.

Technical characteristics

1, no heating

2, has a broad-spectrum bactericidal effect

3. The flavor and quality of the processed food will not be affected

Application area

is mainly suitable for all kinds of beverages, liquid foods, condiments and other various packaged solid foods

Irradiation sterilization

The significance and characteristics of food irradiation

(1) Basic concepts

Food irradiation refers to the use of radiation to irradiate food (including raw materials) to delay the development of certain physiological processes (germination and maturation) of fresh food, or to treat food such as insecticide, disinfection, sterilization, and mold prevention to extend the preservation time. The operation process for the purpose of stabilizing and improving food quality.

(2) Technical Features

1. It can be carried out at room temperature or low temperature. The temperature rise of the food during the processing is very small, which is conducive to maintaining the quality of the food;

2, rays (such as γ-rays) have strong penetrating power, which can irradiate food under packaging and without thawing, and kill pests, parasites and microorganisms deep in the food;

3, irradiated food will not leave any residue;

4. Compared with methods such as frozen food preservation, the radiation preservation method can save energy;

5, can improve the craftsmanship and quality of certain foods;

6. Large investment and special equipment are required to generate radiation (radiation source) and provide safety protection measures to ensure that the radiation does not leak;

7. For different products and different irradiation purposes, it is necessary to select and control the appropriate irradiation dose in order to obtain the best economic and social benefits.

8. The irradiated food should be marked on the label.

The progress of food irradiation at home and abroad

(1) abroad

1896-Minck proved through experiments that X-rays are lethal to protozoa.

1921--Schwatz used X-rays to kill Trichinella Spiralis in meat and obtained a US patent.

1930-Wüst (Wüst) confirmed that "all food is packaged in a sealed metal can, and then irradiated with powerful roentgen rays can kill all bacteria", and obtained a French patent.

After the end of the Second World War--With the massive application of radioisotopes and the advent of mechanical radiation sources such as electron accelerators, the development of radiation processing food was promoted.

1953-Eisehower prompted the U.S. military to study food irradiation.

In 1957, the U.S. military was responsible for the launch of a five-year irradiated food research program, which invested a lot of manpower and material resources.

1960-began to test irradiated food in the US Army.

1963--The first international conference on irradiated food was held in the US military’s Natick Laboratory.

1965-Canada established the world's largest potato irradiation plant.

1970-Experts from FAO/IAEA/WHO established the International Plan for Food Irradiation (IFIP) at the Geneva meeting.

1976-The Food and Agriculture Organization of the United Nations considered that five irradiated products (ie potato, wheat, chicken, papaya and strawberry) are absolutely safe.

1978-There are 80 60Co factories in the world for irradiation disinfection and sterilization (60 of them are used for medical disinfection).

The 1980-FAO/IAEA/WHO meeting concluded that the average absorbed dose of irradiated food is 10 kilograys (kGy) and below, there is no toxicity hazard, and there is no need to conduct toxicity tests.

In 1988, the number of 60Co factories used for irradiation disinfection and sterilization in the world increased to 182, and the world's output of irradiated food was about 500,000 tons.

After 1997-WHO further abolished the upper limit of 10 kGy, and the International Food Regulatory Commission (CAC) has successively proposed general standards and regulations for irradiated food.

(two) domestic

1958--Started food irradiation research work.

Mid 1970s-Many regions in China have successively conducted research on irradiated preserved food. The irradiated varieties include meat, aquatic products, fruits, dried fruits, vegetables, grains, eggs, etc.

80s--Food irradiation has entered a certain scale of production stage

In the early 1990s, nearly 150 irradiation devices were built in my country, of which more than 50 devices were designed with installed capacity of 1.11×1016 bei.

From 1984 to 1997-Food irradiation hygiene standards promulgated by the Ministry of Health basically covered most of the food.

Food irradiation in my country is not only used for preservation, epidemic prevention, medical treatment, etc., but also for processing purposes such as improving product quality.

Radioisotopes and radiation

1, atom

2, isotope

The number of neutrons (N) in the atoms of an element is not exactly the same. If the atoms have the same number of protons (Z) but different numbers of neutrons (N), they are called isotopes of the same element.

3, radioisotope

The decay of unstable isotopes is accompanied by various radiations. These unstable isotopes are called radioactive isotopes.

4, radiation

Radioisotopes can emit α, β (β+ and β-) and γ rays, and the process is called radiation.

(1) α rays (or α particles): a stream of positively charged high-speed particles emitted from the nucleus (positively charged nuclei);

(2) β-ray: a high-speed electron flow (or positron flow) emitted from the nucleus;

(3) γ-ray: is an electromagnetic beam (or photon stream) with a very short wavelength (wavelength 1～0.001nm)

5, ionizing radiation

"" refers to the radiation effect of α, β, γ and other rays, and as a result, it can ionize the irradiated (irradiated) material.

6, α (β or γ) decay

"" means that alpha particles (beta particles or photons) are emitted from the nucleus.

Irradiation unit and dose measurement

(1) Radioactivity intensity and radioactivity ratio

1, radioactivity intensity

, also known as radioactivity, is a physical quantity that measures the strength of radioactivity.

The units used by 　　 are:

(1) Curie (Curie abbreviated as Ci)

If the radioisotope has 3.7×1010 nuclear decays per second, its radioactivity intensity is 1 Curie (Ci).

(2) Becqurel (Becqurel, Bq for short)

1 becque means that the radioactive isotope decays one nucleus every second.

(3) Gram radium equivalent

"When the radioisotope that emits gamma rays (i.e. gamma radiation source) and 1 gram of radium (sealed in a 0.5mm thick platinum filter) have the same ionization effect under the same conditions, the radioactive intensity is called 1 gram of radium equivalent.

2, radioactivity ratio

refers to the concentration of radioactive isotopes in a compound or element as "radioactivity ratio", which is also used to express the radioactivity of a unit quantity of material.

(2) Exposure

"Exposure" is a physical quantity used to measure the ionization ability of X-rays or γ-rays in the air.

The units used by 　　 are:

(1) Roentgen (Roentgen, abbreviated as R)

(2) SI Coulomb/kg (C·kg-1)

(three) absorbed dose

1, absorbed dose unit

(1) Absorbed dose

The energy of the rays absorbed by the irradiated substance is called the absorbed dose, and its units are:

(1) rad (rad)

(2) Gray (Gray, Gy for short).

(2) Dose rate

refers to the energy absorbed per unit mass of irradiated material in unit time.

(3) Dose equivalent

is used to measure the different biological effects caused by different types of radiation, and its unit is Sv (Sv).

(4) Dose equivalent rate

refers to the dose equivalent per unit time, the unit is Sv·s-1 or Sv·h-1.

2, absorbed dose measurement

(1) National benchmark-Frickle dosimeter (ferrous sulfate dosimeter)

(2) National transmission standard dose measurement system-alanine/ESR dosimeter (a free radical type solid dosimeter), cerium sulfate-cerium dosimeter, potassium dichromate (silver)-perchloric acid dosimeter, Silver dichromate dosimeter, etc.

(3) Conventional dosimeters--colorless transparent or red plexiglass sheet (polymethyl methacrylate), cellulose triacetate, nylon or PVC based radiation color film containing leuco dye, etc.

Radiation source and food irradiation device

(1) Radiation source

1, radioisotope

(1) Cobalt-60 (60Co) radiation source

(2) Cesium-137 (137Cs) radiation source

2, electron accelerator

is a device that uses electromagnetic fields to obtain higher energy for electrons and convert electrical energy into rays (high-energy electron rays, X-rays).

(1) electron beam

Electron beam is also called electron flow or electron beam. The higher the energy, the stronger the penetrating ability.

The electron density of the electron accelerator is high, the electron beam (ray) has a short range and poor penetrating ability, so it is generally applicable Irradiation on the surface of food.

(2) X-ray

The high-energy electrons produced by the accelerator hit the heavy metal target to produce X-rays with energy ranging from zero to the energy of the incident electron.

(2) Protective equipment

The materials commonly used for protective equipment are:

1. Lead-lead containers can be used to store radiation sources

2, steel-the structural skeleton of vessels and equipment

3. Iron--used to make protective doors, iron hooks and covers, etc.

4. Water-store radiation sources (such as 60Co, 137Cs, etc.) in deep wells

5. Concrete wall-both a building structure and a shield

(3) Conveying and safety system

Industrial food irradiation equipment is based on the radiation source, and is equipped with strict safety protection facilities and automatic transportation and alarm systems. All operating equipment, automatic control, alarm and safety systems must be combined extremely tightly.

Physical effects of food irradiation

(1) The interaction of alpha rays and gamma rays with substances

1, photon

2, Optoelectronics

3, Compton scattering

(2) The role of electron beams

1, Coulomb scattering

2, Bremsstrahlung

3, Cerenkov effect

The chemical effects of food irradiation

(2) protein and enzyme

1, cause the breakage of disulfide bonds, hydrogen bonds, salt bonds and ether bonds in some proteins

2. Promote changes in the primary structure of the protein

3. Deamination, decarboxylation and oxidation occur

4. The protein aqueous solution will be cross-linked by radiation after irradiation

5. Most food enzymes have great resistance to the radiation effect, which is helpful for the irradiation treatment of enzyme preparations.

(Three) sugar

1. After irradiated, pure sugars have obvious degradation effects and formation of radiolysis products

2. The degradation effect of the mixture is usually smaller than the radiolysis effect of a single component.

(Four) lipids

is mainly radiation-induced self-oxidation products and non-oxidized radiation products, so saturated fatty acids are relatively stable, unsaturated fatty acids are easily oxidized, and decarboxylation, hydrogenation, and deamination can occur.

(five) vitamins

1, fat-soluble vitamins

(1) The most sensitive: Vitamin A and E

(2) Stable: Vitamin D

2, water-soluble vitamins

(1) The most sensitive: Vitamin B1 and C

The number of vitamins lost by irradiation is affected by the dose, temperature, the presence of oxygen and the type of food. Generally speaking, irradiation under anaerobic or low temperature conditions can reduce the loss of any vitamins in food.

(6) Food packaging materials

Under irradiation pasteurization conditions (10～30kGy), the properties of all films used for packaging food are basically not affected, and they do not pose a hazard to food safety.

Biological effects of food irradiation

The biological effects of food irradiation are related to the chemical changes in the organism, and the doses necessary for different substances to achieve various biological effects are different.

(1) Microbe

Radiation preservation is mainly to directly control or kill spoilage microorganisms and pathogenic microorganisms in food.

Ionizing radiation to kill microorganisms is generally expressed by the dose (Gy) required to kill 90% of the microorganisms, that is, the Gy dose required when the number of remaining microorganisms drops to 10% of the original number, and is expressed by the D10 value.

1, bacteria

2, yeast and mold

3, virus

(two) insects

1, insects

2, parasites

(three) fruits and vegetables

1, suppress peak breathing

2, change the chemical composition of fruits and vegetables

3. Affect the metabolic reaction of fresh vegetables

4, inhibit germination

Food irradiation application

Classified according to the purpose of food irradiation application and the required dose:

The application of irradiation on food

1, Radurization (Radurization)

The main purpose of this irradiation treatment is to reduce the number of spoilage microorganisms and other organisms in the food, and to extend the post-ripening period and preservation period of fresh food (such as inhibiting germination, etc.). The general dose is below 5kGy.

2, irradiation pasteurization (Radicidaton)

This kind of irradiation treatment prevents the detection of specific non-spore-free pathogenic bacteria (such as Salmonella) in the food. The radiation dose used ranges from 5 to 10 kGy.

3, Radappertization (Radappertization)

The radiation dose used can reduce the number of microorganisms in food to zero or a limited number. After this irradiation treatment, the food can reach a certain storage period under normal conditions without re-contamination, and the dose range is greater than 10kGy.

Food Irradiation Process

(1) Food Irradiation Preservation

1, fruits and vegetables

(1. Purpose

① Prevent the spoilage of microorganisms

② Control pest infection and spread

③ Delay the maturation period and prevent aging.

(2) Selection of dose

(3) Co-processing with other preservation methods

2, food

The main purpose of 　　 is to avoid or reduce mold rot and deterioration caused by insect damage and mold activities, that is, insecticide and mildew.

3. Livestock, poultry and aquatic products

usually requires a synergistic effect with heat treatment or low temperature.

4, spices and condiments

Irradiation treatment can not only control insect damage, but also reduce the number of microorganisms, ensure the quality of raw materials, and avoid the adverse effects of traditional methods such as heat treatment and chemical treatment.

5. Eggs

Eggs are mainly used to irradiate the pasteurization dose to kill Salmonella.

(2) Irradiation changes food quality

1. Soybeans: Reduce intestinal flatulence factors after germination

2. Wheat: Improve flour quality

3, grapes: juice yield

4. Dehydrated vegetables: greatly shorten the rehydration time

5. Liquor: Irradiation aging

(3) Other applications of irradiation

Another important application of food irradiation is the quarantine treatment of fruits and vegetables.

Factors affecting the effect of food irradiation

(1) Irradiation dose

1, the purpose of irradiation

2, irradiated varieties

3, the intensity of the radiation source

4. The physical and chemical effects of food irradiation

5. Dose rate

6, safety protection equipment

(2) The state of the food when it is irradiated

1. Type of food

2. Food chemical composition and organizational structure

3, food growth and development stage, maturity status, respiratory metabolism rate

4. Type and quantity of contaminated microorganisms and pests

(3) Environmental conditions during irradiation

1, oxygen

2, temperature

(4) Synergistic effect of irradiation and other preservation methods

1. Irradiation at low temperature

2, add free radical scavenger

3, use radiation sensitizer

4. Use with other preservation methods

5. Select the appropriate irradiation device.

The safety of irradiated food

(1) Subject areas involved in safety testing and evaluation

1, Toxicology

2, Nutrition

3, Microbiology

(2) Conclusion

1, World Health Organization (WHO)

(1) Irradiation will not cause toxic changes in food ingredients that have adverse effects on human health;

(2) Irradiated food will not increase microbiological hazards;

(3) Irradiated food will not cause loss of nutrition supply

2. Joint meeting of the Food and Agriculture Organization of the United Nations, the International Atomic Energy Agency and the World Health Organization

Foods irradiated under normal irradiation doses are safe

Regulations on the management of irradiated food

(1) Internationally

1. In 1983, the FAO/WHO International Food Regulatory Commission adopted the "General Standards for Irradiated Foods (Worldwide Standards)" and "Recommended Practices for the Operation of Irradiation Equipment for Food Processing".

2. In 1984, the International Advisory Group on Food Irradiation (ICGFI) was established

(two) domestic

1, GB10252-88 Radiation protection regulations for 60Co devices for radiation processing

2, GB8703-88 Radiation Protection Regulations

3, GB14891, 1~GB14891, 10-94 irradiated food standard

4. In 1996, the Ministry of Health issued the "Administrative Measures for the Hygiene of Irradiated Food"