Abstract: The actual packaging effect sometimes differs greatly from the expected results, mainly due to changes in the gas composition in the package. This article will introduce the reasons for the changes in the gas composition in the package and the detection methods.
Keywords: food, medicine, headspace, sealing, barrier testing
It is well known that oxygen, water vapor and other gases are the main factors causing deterioration of foods and drugs. Therefore, cutting off the source of oxygen or water vapor in the package and controlling the gas components inside the package can effectively extend the shelf life of the product and improve the preservation effect. Therefore, new packaging such as MAP packaging, CAP packaging, vacuum packaging and other barrier packaging materials have been used more and more widely. However, although we have adjusted the gas composition in the package and used high barrier materials to block the infiltration of oxygen, water vapor and other gases from the outside, sometimes the actual packaging effect will be quite different from the expected results. This article will introduce the reasons for the changes in the gas composition in the package and the detection methods.
1. Gas analysis in the package
After the packaging is completed, the gas composition will be temporarily stabilized. However, as the storage time of the product is prolonged, the content of oxygen or other product sensitive gas inside the package will gradually change, thereby changing the composition of the gas inside the package, and thus affecting the quality of the product. The analysis shows that the increase in the content of oxygen, water vapor and other gases inside the package is mainly caused by the following two types of reasons.
First, it is the gas from the outside of the package. There are two ways in which gas enters the package: infiltration and leakage, the biggest difference between which is the amount of gas that is transmitted and the location through which it is transmitted. Permeation means that the gas enters the surface of the material from the high concentration side and diffuses to the low concentration side through the material. The speed of penetration depends mainly on the barrier properties of the packaging material. The selection of high barrier materials for packaging can effectively solve this problem. The leakage is caused by gas leaking through the cracks of the material, micropores or small gaps between the two materials or entering the package. The probability of leakage in the heat-sealed portion of the package and the mouth of the container is high. To solve this problem It is necessary to strictly control the production process and timely adjust the process according to the test data. As a package, penetration and leakage are present at the same time, so you should pay attention to the combined effect of the two when testing.
Second, it is the gas from inside the package. It mainly includes residual gas and product adsorption gas. The residual gas is a gas such as a certain concentration of oxygen remaining inside the package after the end of the packaging process (when the package is sealed). Although the packaging process of MAP packaging, CAP packaging, and vacuum packaging has the operation of replacing and degassing the internal gas of the package (especially the oxygen therein), the effect of degassing is not due to the limitation of operation accuracy and time. Well, even the so-called "vacuum packaging" is only to minimize the gas content in the package and can not achieve the complete elimination effect. The adsorption of gas by the product requires special attention because the materials other than metal and glass have a certain gas adsorption function, and the total amount of gas adsorbed is related to the looseness of the material and the gas contact time. However, adsorption is not equal to absorption. When the original atmospheric environment in the package changes, the decrease in gas concentration in the package causes the gases previously adsorbed on the surface of the product to be "released" again.
2. Detection method
Although the change of gas composition inside the package is relatively slow, this change will still affect the shelf life of the product. Therefore, the manufacturer has adopted various possible gas control methods to minimize the increase of oxygen and water vapor content inside the package. For example, the use of a multi-layer barrier packaging material to improve the barrier properties of the package, the addition of a desiccant, absorbent or oxygen scavenger in the material, inside the bottle cap or other locations, not only can absorb the original residual gas in the package, for external gases Infiltration is also an effective layer of protection. But what about the effectiveness of these measures? This requires a test analysis of the package to judge. The following describes the detection methods for the reasons for the changes in the gas composition of several packages mentioned in the previous section.
2.1 Barrier testing
Barrier testing is important for packages that use high barrier materials. In the past, we were only able to detect the barrier properties of films and sheets. However, the packaging forms we saw in actual packaging are containers, bags, etc. The barrier properties of the test materials can only give a reference for the final packaging material selection. Value, but can not explain the overall barrier properties of the final package, because the thickness of the package is not uniform, and the material properties have changed during the production process, so the estimation results often have a certain gap with the actual test results. Based on this, not only should the barrier properties of the packaging material be tested, but also the overall barrier properties of the packaging material should be tested. Combining the two aspects of the data can determine whether the material selection is correct. At present, the whole method for detecting oxygen permeability and moisture permeability of the container has developed to some extent, and the corresponding testing equipment has also been developed, which can well meet the barrier detection requirements of the whole package (Fig. 1 is developed by Labthink). PERME series TOY-C1 isobaric film/container oxygen permeability meter for container oxygen permeability test; Figure 2 is PERME series TSY-W3 electrolysis water vapor transmission rate tester for container moisture permeability test).
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Figure 1. PERME Series TOY-C1 Isobaric Film/Container Oxygen Permeator
Figure 2. PERME Series TSY-W3 Electrolytic Water Vapor Transmission Rate Tester
2.2 Sealing test
Detecting the sealing properties of the package can indicate the leakage of the package. If the gas or liquid leaks out of the package or enters the package, it will accelerate the deterioration of the contents while making the barrier properties of the packaging material useless. However, for each specific form of packaging, the indicators related to sealing performance are different. For heat-sealed bags, the high-temperature treatment of the heat-sealing operation will affect the mechanical strength of the nearby packaging materials, so the material near the heat-sealing edge will often become the weak point of the tightness of the flexible packaging bag; In fact, the pressure distribution in the bag is not uniform, and the position where the leak first occurs is the part with the lowest compressive strength. Therefore, in order to correctly evaluate the sealing performance of the flexible bag, the finished product must be tested. The method of detecting the overall tightness of the flexible packaging bag mainly relies on the pressure in the bag. Therefore, when testing the sealing performance of the flexible packaging bag, we need to form a pressure difference inside and outside the flexible packaging bag to simulate its actual pressure state. The method has a positive pressure method. Inflating in the bag directly increases the pressure inside the bag. Labthink's PARAM series LSSD-01 leak and seal strength tester uses this method) and negative pressure method (by vacuuming to reduce the pressure outside the bag, Typical products are Labthink PARAM Series MFY-01 Sealing Tester. For the container packaging with thread sealing method, the sealing performance of the cap that reflects the plastic bottle cap and the bottle mouth is the primary factor affecting the overall sealing performance of the plastic container. The related testing can also pass the Labthink PARAM series LSSD. The -01 leak is performed with a seal strength tester.
2.3 Headspace analysis
For those gases that remain inside the package, they cannot be ignored because of the end of the packaging process. The gas components inside the package are difficult to control and change by other technical means from the end of filling to the time of opening the package. The use of barrier packaging materials can only hinder the infiltration/exudation of the packaging material. Eliminate the existing oxygen and other gases inside the package (not including the addition of oxygen removal technology to the package). If the residual gas content exceeds the highest concentration requirement for product preservation, the shelf life requirements of the product cannot be met regardless of the high-barrier materials and the well-established sealed packaging form. Therefore, we need to detect the gas components remaining in the package and adjust the packaging process accordingly.
Residual gases as well as product adsorbed gases can be obtained by detecting the headspace of the package, which detects the gas components that collect at the top of the package, with only a difference in detection time. If residual gas is to be detected, it needs to be tested immediately after the end of the packaging process; however, if the product is to be adsorbed, it should be carried out after the end of the packaging process, and it should be tested several times as the product is extended. The gas concentration curve is plotted for comprehensive analysis because gas desorption from the surface of the product is also a very slow process. This type of inspection can be done with the Labthink PARAM Series HGA-01 Headspace Air Analyzer. Of course, we can also accelerate the desorption of gas adsorbed on the surface of the product by reducing the specific gas concentration in the packaging environment.
3. Summary
In summary, although the change of gas composition in the package is difficult to avoid, we can comprehensively judge whether the product can reach the expected value by detecting the overall barrier property of the package, the sealing property of the package, and the composition change of the headspace inside the package. Shelf life, through these tests we can also find the weak links in the packaging design, to provide accurate test data to further improve the packaging structure.