As we all know, oxygen has a great influence on the quality of food, and there are also some food packaging (such as carbonated drinks, coffee, etc.) have strict requirements on the amount of CO2, so control the permeability of food packaging materials and organic packaging Gas content has become one of the main tasks of food packaging.
1. The effect of gas transmission on the quality of food contents
1. Oxidize the fats and oils in foods. This oxidation can be carried out even under low temperature conditions. The peroxide produced by the oxidation of oils and fats not only causes the food to lose its food value, but also causes offensive odors and toxic substances.
2. Most of the bacteria in foods reproduce and grow due to the presence of oxygen, resulting in spoilage and deterioration of the food.
3. If fresh fruits and vegetables do not take necessary protective measures in the process of storage and transportation, fruits and vegetables will absorb oxygen due to respiration and release CO2 and water, and consume part of the nutrients, making vegetables, fruits appear excessively cooked, soft, flavor changes, etc. Happening.
4. At room temperature, the reaction speed of oxidation browning is much faster than heating browning. For flavored foods, such as concentrated broth and easily oxidized brown discolored foods, even a small amount of residual oxygen can cause browning and cause the flavor of the food to be lost or deteriorated.
5. Carbonate, beer, coffee, fruit juice and other products are not only sensitive to oxygen but also have a great influence on their quality.
2. Introduction to main methods of breathability test
In order to prevent the occurrence of the above-mentioned situation, it is necessary to test the gas permeability of the food packaging to ensure the gas barrier property of the packaging material. Divided from the test principle, the air permeability test method can be divided into two categories: differential pressure method and coulometric sensor method.
Differential pressure test principle: The test chamber is divided into two separate spaces with the film to be tested, and the test gas is injected into one side (high pressure chamber) to form a certain pressure difference on both sides of the sample. The permeation rate of the gas can be determined by measuring the pressure or volume change of the low pressure chamber by permeating the membrane to the low pressure chamber. The pressure difference method is adopted in GB/T1038-2000, and the relevant international standards, such as: ASTM D1434-1998, ISO 15105-1, ISO 2556:2001, etc. also adopt differential pressure method.
The coulometric sensor method test principle: The test chamber is divided into two independent gas flow systems with a film to be measured, and the gas to be tested flows on one side (a pure oxygen or mixed gas containing oxygen can be used to set the relative humidity of the gas. ), the other side is flowing nitrogen. The pressure difference on both sides of the sample is the same but the oxygen partial pressure is different. Under the effect of the concentration difference, the oxygen passing through the film is sent to the electricity analysis sensor under the nitrogen gas flow, so as to calculate the oxygen permeability of the material.
The differential pressure and isobaric methods have different test principles. The test conditions are different. The unit of the test results is also different (the unit of the differential pressure method is cm3/m2•24h•0.1MPa, while the unit of equal pressure method is cm3/m2• d) Therefore, the uncorrected raw data obtained from these two test methods is theoretically not comparable. However, after using a standard membrane to calibrate an isobaric apparatus and applying the correction factor to a formal test, the test results for the differential pressure method and the equal pressure method can be compared.
Due to the support of membrane technology theory, differential pressure method has always been used as a basic method in gas permeability testing, and scientific research and testing organizations mostly use this method. Its outstanding advantage is that it is not selective for the test gas and it is very versatile for different test gases. With the advancement of vacuum gauge detection technology and the application of vacuum technology in equipment design, the detection accuracy of equipment and the repeatability of test data have been greatly improved.
The sensor method appears with the maturation of the oxygen detector technology. Since the sensor used is a consumable component, the calibration factor obtained by the calibration of the device is not valid for a long period of time, and periodic calibration of the device is required according to the requirements, and when the sensor When the loss reaches a certain level, it must be replaced. The lifespan of the sensors of different manufacturers' equipments will vary greatly. The oxygen sensors used by Labthink's oxygen permeability instrument series are expected to use for 12-30 months under normal conditions, which is considered to be a long time to use. .
3, the conclusion
The penetration of gas into the packaging material may cause deterioration and corrosion of the food, which has a great influence on the shelf life of the food. In the world, there are two methods, differential pressure method and electric quantity analysis sensor method, to detect gas permeability. The flexible packaging testing industry in China has rapid development in the area of ​​air permeability testing.
1. The effect of gas transmission on the quality of food contents
1. Oxidize the fats and oils in foods. This oxidation can be carried out even under low temperature conditions. The peroxide produced by the oxidation of oils and fats not only causes the food to lose its food value, but also causes offensive odors and toxic substances.
2. Most of the bacteria in foods reproduce and grow due to the presence of oxygen, resulting in spoilage and deterioration of the food.
3. If fresh fruits and vegetables do not take necessary protective measures in the process of storage and transportation, fruits and vegetables will absorb oxygen due to respiration and release CO2 and water, and consume part of the nutrients, making vegetables, fruits appear excessively cooked, soft, flavor changes, etc. Happening.
4. At room temperature, the reaction speed of oxidation browning is much faster than heating browning. For flavored foods, such as concentrated broth and easily oxidized brown discolored foods, even a small amount of residual oxygen can cause browning and cause the flavor of the food to be lost or deteriorated.
5. Carbonate, beer, coffee, fruit juice and other products are not only sensitive to oxygen but also have a great influence on their quality.
2. Introduction to main methods of breathability test
In order to prevent the occurrence of the above-mentioned situation, it is necessary to test the gas permeability of the food packaging to ensure the gas barrier property of the packaging material. Divided from the test principle, the air permeability test method can be divided into two categories: differential pressure method and coulometric sensor method.
Differential pressure test principle: The test chamber is divided into two separate spaces with the film to be tested, and the test gas is injected into one side (high pressure chamber) to form a certain pressure difference on both sides of the sample. The permeation rate of the gas can be determined by measuring the pressure or volume change of the low pressure chamber by permeating the membrane to the low pressure chamber. The pressure difference method is adopted in GB/T1038-2000, and the relevant international standards, such as: ASTM D1434-1998, ISO 15105-1, ISO 2556:2001, etc. also adopt differential pressure method.
The coulometric sensor method test principle: The test chamber is divided into two independent gas flow systems with a film to be measured, and the gas to be tested flows on one side (a pure oxygen or mixed gas containing oxygen can be used to set the relative humidity of the gas. ), the other side is flowing nitrogen. The pressure difference on both sides of the sample is the same but the oxygen partial pressure is different. Under the effect of the concentration difference, the oxygen passing through the film is sent to the electricity analysis sensor under the nitrogen gas flow, so as to calculate the oxygen permeability of the material.
The differential pressure and isobaric methods have different test principles. The test conditions are different. The unit of the test results is also different (the unit of the differential pressure method is cm3/m2•24h•0.1MPa, while the unit of equal pressure method is cm3/m2• d) Therefore, the uncorrected raw data obtained from these two test methods is theoretically not comparable. However, after using a standard membrane to calibrate an isobaric apparatus and applying the correction factor to a formal test, the test results for the differential pressure method and the equal pressure method can be compared.
Due to the support of membrane technology theory, differential pressure method has always been used as a basic method in gas permeability testing, and scientific research and testing organizations mostly use this method. Its outstanding advantage is that it is not selective for the test gas and it is very versatile for different test gases. With the advancement of vacuum gauge detection technology and the application of vacuum technology in equipment design, the detection accuracy of equipment and the repeatability of test data have been greatly improved.
The sensor method appears with the maturation of the oxygen detector technology. Since the sensor used is a consumable component, the calibration factor obtained by the calibration of the device is not valid for a long period of time, and periodic calibration of the device is required according to the requirements, and when the sensor When the loss reaches a certain level, it must be replaced. The lifespan of the sensors of different manufacturers' equipments will vary greatly. The oxygen sensors used by Labthink's oxygen permeability instrument series are expected to use for 12-30 months under normal conditions, which is considered to be a long time to use. .
3, the conclusion
The penetration of gas into the packaging material may cause deterioration and corrosion of the food, which has a great influence on the shelf life of the food. In the world, there are two methods, differential pressure method and electric quantity analysis sensor method, to detect gas permeability. The flexible packaging testing industry in China has rapid development in the area of ​​air permeability testing.
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