Application of barrier property testing in dairy packaging

In recent years, with the sustained and stable development of China's economy and the continuous improvement of people's living standards, the dairy industry has entered a golden period of development and has become one of the fastest-growing and most promising industries in China's food industry. Today, milk and dairy products have become one of the symbols of healthy life, and various dairy products have extensive sales networks. However, with the different sales environments, it is difficult to ensure that dairy products are stored in a continuous and stable environment (even fresh milk is difficult to provide a low-temperature refrigerated environment from beginning to end), so the impact of dairy packaging on the quality of dairy products is very large. The quality of packaging can directly affect the shelf life of dairy products, and then it is related to the safety of consumers.

1 The main reasons affecting the quality of dairy products and the corresponding packaging forms

Dairy packaging, as an integral part of dairy products, has a profound impact on the development of the dairy industry. Because milk is easy to deteriorate, both long-life milk (UHT) and fresh milk have strict quality requirements for packaging. Here we mainly introduce three categories: fresh milk, fermented milk and milk powder.

1.1 Fresh milk

Fresh milk can be processed into different types of dairy products, and each product has different packaging requirements according to its own preservation characteristics. The most common ones are pasteurized milk and ultra-high temperature sterilized milk (UHT milk).

Pasteurization is the most widely used method for processing fresh milk. It usually uses high-temperature instantaneous sterilization, that is, heating the raw milk to 70℃~72℃ for 10~20s. Pasteurization mainly kills bacteria in raw milk to ensure quality and drinking safety; it can also eliminate other microorganisms and enzymes that can cause flavor changes to extend the shelf life of fresh milk. However, pasteurization can generally only kill 90%~99% of microorganisms in milk, so its shelf life is not very long, and the required storage environment is low temperature refrigeration. Light is an important cause of vitamin loss in pasteurized milk, and other nutrients will also decompose due to photochemical reactions, so dairy packaging needs to be protected from light. Oxygen is also one of the important factors that cannot be ignored. If there is too much oxygen in the top gap of the package, or the container is too permeable to oxygen, the oxidation reaction of the dairy in the package will be aggravated and the quality will drop rapidly. Commonly used packaging includes glass bottles, composite cartons and plastic bags.

Ultra-high temperature sterilization allows fresh milk to continue to flow through the heating process, at a high temperature (at least 135°C) for a short time (1s to 2s), and then aseptically packaged. The loss of nutrients in ultra-high temperature sterilized milk (UHT milk) during storage depends on the storage temperature, the initial oxygen content in the milk and the properties of the packaging material (oxygen permeability and light transmittance). Odors produced by oxidation reactions and fatty acid rancidity will also enter UHT milk. The expansion of these reactions depends on the oxygen content in the milk and the storage temperature. Various types of packaging can be used to package UHT milk. Composite materials lined with aluminum foil are the most commonly used to package UHT milk. The aluminum foil layer is the main barrier layer, which can not only effectively prevent the penetration of oxygen but also preserve the flavor components in the fresh milk.

1.2 Fermented milk

Fermented dairy products are products made from fresh milk or its products after homogenization, sterilization and other process operations, and then fermented by microorganisms (such as the very popular yogurt, sour milk, and yogurt). Yogurt is a typical fermented dairy product. Different types of products can also be formed after adding fruits, fruit flavors or sugars. According to its existence form, it can be divided into: coagulated type (hard), stirred type (paste) and liquid type. Unlike fresh milk, the carbon dioxide content in fermented milk has an important influence on the change of flavor and the growth of microorganisms. At present, the packaging form of fermented milk is also glass bottles, composite paper boxes and plastic bags (plastic containers, plastic cups).

1.3 Milk

powder Milk powder is also a dairy product with a large consumption. It is made by spray drying fresh milk or dairy products. The oxidation reaction is one of the main factors determining the shelf life of milk powder. To ensure or extend the shelf life of milk powder, it must be sealed and packaged to reduce the impact of oxygen on the quality of milk powder. However, it should be noted that unlike liquid dairy products, the moisture resistance and oxygen barrier of milk powder packaging are as important. Commonly used packaging forms include metal cans, aluminum foil composite soft packaging bags, and paper-based composite cans.

2 Important test items for dairy packaging

Through the description in the previous part, everyone should be able to summarize that light and the penetration of oxygen and water vapor are the main factors affecting the quality of dairy products. Among them, it is completely possible to protect dairy products from light. The dairy packaging materials currently used have basically achieved good light blocking. However, the realization of barrier properties is not so simple. On the one hand, it is directly related to the high cost of barrier materials. To achieve the ideal packaging barrier property, the packaging cost will inevitably be high, which will eventually lead to an increase in product production costs. On the other hand, the multi-layer composite method is a very suitable and effective way to improve the barrier property for composite paper boxes, composite plastic soft packaging bags or composite plastic cups. However, the level of independent research and development of corresponding multi-layer composite production equipment and raw materials in China is still insufficient, and they mainly rely on imports. This is particularly prominent in the packaging of composite paper boxes. Therefore, although the current situation of high dairy packaging costs has attracted widespread attention, it is still very difficult to replace this high-cost packaging material. [page]

In addition, with the reduction of the barrier property of the packaging material used, the oxygen and water vapor that penetrate into the packaging will increase, or the filling gas in the packaging will seep out of the packaging faster, which will eventually lead to an increase in the oxygen content and humidity in the packaging, which are the main reasons for the deterioration of dairy products and dairy products. Therefore, it can be said that in a certain sense, for the same kind of dairy or dairy products (with the same processing technology), the barrier property of the packaging material is the main determinant of its shelf life. Therefore, the barrier property test of packaging materials is very important for dairy and dairy products.

How much impact will the different barrier properties of packaging materials have on the shelf life of dairy products? Here are some representative barrier property test data of dairy packaging materials that we have tested, and the difference will be clear at a glance. The equipment used for the test is Labthink VAC-V1 gas permeability tester (gas permeability test) and TSY-T3 moisture permeability tester.

Note: The unit of oxygen permeability is: m1/m2•24h•0.1MPa; the unit of moisture permeability is: g/m2•24h

The samples listed in the table basically include all the packaging materials required for dairy products and dairy product packaging, such as the paper-plastic-aluminum composite materials used in composite cartons such as ridge packs and Tetra Pak, the coating/composite packaging film used in aseptic packaging, the most commonly used PE black and white film in mass packaging, and the AL composite plastic flexible packaging film used in milk powder packaging. From the data in the table, it can be seen that the paper-plastic-aluminum composite materials used in composite cartons and the AL composite plastic flexible packaging film used in milk powder packaging have the best barrier properties among various dairy packaging materials, and the air permeability and moisture permeability data are in the high barrier range. Of course, the corresponding cost is also very high. According to relevant information, the cost of a Tetra Pak is not less than 0.5 yuan. The coating/composite packaging film used in aseptic packaging is second, belonging to the medium barrier range, and the cost is moderate. The most common PE black and white film and milk film in packaging have the worst barrier properties. The air permeability data alone is thousands of times higher than that of paper-plastic-aluminum composite materials and AL composite plastic flexible packaging films, and hundreds of times higher than that of coating/composite packaging films. Of course, the price is also the lowest, often less than 0.1 yuan.

The selection of packaging materials, material structure and barrier properties are all determined in accordance with the product's expected shelf life. For example, dairy products or dairy products packaged with high barrier properties of paper-plastic-aluminum composite materials and AL composite plastic flexible packaging films can often have a shelf life of several months, and the storage environment requirements are not very high. Basically, they do not need to be stored in a refrigerated environment. If materials with low barrier properties are used, it is likely to cause a large number of products to deteriorate prematurely, or bring greater difficulties to transportation and storage. The shelf life of dairy products packaged in black and white film is only a few days. This type of product is often consumed in large quantities and is a type of product that is produced and sold quickly. If the barrier properties of the packaging material used are too good (for example, the use of medium barrier materials) will not significantly extend the shelf life, but will increase the packaging cost of the product. Therefore, the packaging material must be selected according to the characteristics of the product and the shelf life. At the same time, the barrier properties of the packaging material can also be "customized" according to the needs of the product, that is, the structure of the material is designed according to the required barrier properties and the corresponding materials are selected. From the data in the table, we can see that both are paper-plastic-aluminum composite materials, but the gas barrier property of sample 2# is not as good as that of sample 1#, while the moisture barrier property is better; both are PE films, but some have a barrier property of more than 900, while others have to reach more than 1300. The improvement of barrier property is sufficient to increase the cost. Therefore, as long as the packaging material can ensure the quality of the product during the shelf life, there is not much benefit in the one-sided pursuit of barrier property.

3 Summary

At present, China's domestic dairy packaging materials can meet the general shelf life needs (combined with the barrier property, light-proof property, mechanical properties and sealing property of the material), but high-end dairy packaging still needs to rely on imports. However, with the continuous introduction of new products in the dairy industry and the promotion of new processing technology, the research and development of new packaging forms and the use of packaging materials have also entered a period of rapid development. However, the requirements for material selection are higher. Only by conducting complete testing of various properties of the material can the quality of dairy products and the safety of consumers be better guaranteed. (end)