Abstract: Based on the main quality influencing factors in the preservation of dairy products and dairy products, this paper introduces the application of barrier testing in dairy packaging, and discusses the relationship between the barrier properties of packaging materials and the shelf life of products.
Key words: dairy products, fresh milk, fermented milk, milk powder, barrier properties, oxygen permeability, moisture permeability In recent years, with the continuous 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. Become one of the fastest growing and most profitable industries in China's food industry. Nowadays, milk and dairy products have become one of the symbols of healthy living, and all kinds of dairy products and dairy products have an extensive sales network. However, with the different selling environment, it is difficult to ensure that the dairy products are stored in a stable and stable environment (even if the storage of fresh milk is difficult to provide a low-temperature refrigeration environment from beginning to end), so the impact of dairy packaging on the quality of dairy products is very large. . The quality of the packaging can directly affect the shelf life of the dairy product, which in turn is related to the consumer's food safety.
1. The main reasons affecting the quality of dairy products and the corresponding packaging form Dairy packaging as an integral part of dairy products has a profound impact on the development of the dairy industry. Because milk is prone to deterioration, both long-acting milk (UHT) and fresh-keeping milk impose stringent quality requirements on the packaging. Here, the main categories are 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 storage characteristics. The most common are pasteurized milk and ultra-high temperature fire milk (UHT milk).
Pasteurization is one of the most widely used methods for the treatment of fresh milk. It is usually sterilized by high temperature, that is, the raw milk is heated to 70 ° C ~ 72 ° C for 10 ~ 20 s. Pasteurization mainly kills bacteria in raw milk to ensure the quality and safety of drinking. It also eliminates other microorganisms and enzymes that can cause flavor changes to prolong the shelf life of fresh milk. However, pasteurization generally only kills 90% to 99% of the microorganisms in the milk, so its shelf life is not very long, and the required preservation environment is low temperature refrigeration. Light is an important cause of vitamin loss in pasteurized milk. Other nutrients are also decomposed by 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 headspace of the package, or if the container is too permeable to oxygen, the oxidation reaction of the dairy in the package will be intensified and the quality will drop rapidly. Commonly used packaging is glass bottles, composite cartons and plastic bags. Ultra-high temperature sterilization allows fresh milk to continue to flow through the heating process and undergo a short period of time (1 s to 2 s) at high temperatures (at least 135 ° C), followed by aseptic packaging. The loss of backing components of UHT milk during storage depends on the storage temperature, the amount of starting oxygen in the milk, and the nature of the packaging material (permeability to oxygen and light transmission). The odors from oxidation and fatty acid loss also enter the UHT milk. The expansion of these reactions is determined by the oxygen content and storage temperature in the milk. Various types of packaging can be used to package UHT milk. UHT milk is most commonly used in aluminum foil-clad composite packaging. The aluminum foil layer is the main barrier layer, which not only prevents oxygen from penetrating but also preserves flavor components in fresh milk. .
1.2 Fermented milk Fermented dairy products are products made by the fermentation of homogenized or sterilized fresh milk or by microbial fermentation (for example, yogurt, sour milk, yogurt, etc., which are of course very popular). Yogurt is a typical fermented dairy product. Different types of products can be formed after adding fruits, fruit flavors or sugars. According to its existence form, it can be divided into: solidified type (hard type), stirred type (paste type) and liquid type. Unlike fresh milk, the carbon dioxide content of fermented milk has an important effect on flavor changes and microbial growth. Currently, fermented milk is also packaged in glass bottles, composite cartons, and plastic bags (plastic containers, plastic cups).
1.3. Milk powder Milk powder is also a kind of dairy product with a large consumption. It is made by spray drying of fresh milk or milk products. The oxidation reaction is one of the main factors in the shelf life of the secondary milk powder. To ensure or extend the shelf life of the milk powder, it must be sealed and packaged to reduce the effect of oxygen on the quality of the milk powder. However, it is important to note that unlike liquid dairy products, the moisture barrier of milk powder packaging is as important as oxygen barrier properties. Commonly used packaging forms include metal cans, aluminum foil composite flexible packaging bags, and paper-based composite cans.
2. Important testing items for dairy packaging By the description of the previous section, we should be able to summarize that the penetration of light, oxygen and water vapor is the main influencing factor of dairy quality. Among them, dairy products are completely achievable. The dairy packaging materials currently used have basically achieved good barrier to light. However, the realization of barrier properties is not so simple, on the one hand, the cost of barrier materials. Expensive is directly related. To achieve the ideal packaging barrier, the cost of packaging will be high, which will eventually lead to an increase in the production cost of the product. On the other hand, it will be a multi-layer composite method, whether it is for composite carton, composite plastic flexible packaging bag or composite. Plastic cups are a very suitable way to effectively improve the barrier properties. However, the corresponding multi-layer composite production equipment and raw materials are still insufficiently developed in China, mainly relying on imports, which is particularly prominent in the packaging of composite carton. Therefore, although the current situation of high cost of dairy packaging has attracted wide attention, it is still very difficult to replace such high-cost packaging materials.
In addition, as the barrier properties of the packaging materials used decrease, oxygen and water vapor permeate into the package may increase, or the filling gas in the package may ooze out of the package, eventually resulting in an increase in oxygen content in the package. And the increase in humidity, which is the main cause of deterioration of dairy products and dairy products. Therefore, it can be said that in a certain sense, for the same dairy or dairy product (the process of processing is consistent), the barrier property of the packaging material is the main determinant of its shelf life. Therefore, barrier testing of packaging materials is essential for dairy and dairy products.
How much difference in the barrier properties of packaging materials will have a significant impact on the shelf life of dairy products? Here are some of the representative barrier test data for the representative dairy packaging materials we tested. The difference is clear at a glance. The equipment used for the test was a Labthink VAC-V1 gas permeator (gas permeability test) and a TSY-T3 moisture permeability tester.
The samples listed in Table 1 basically contain all the packaging materials required for dairy and dairy product packaging, such as paper-plastic aluminum composite materials used in composite carton packs such as ridge bags and Tetra Pak, as used in aseptic packaging. The coating/composite packaging film, the PE black and white film most commonly used in mass packaging, and the AL composite plastic flexible packaging film for milk powder packaging. From the data in the table, it can be seen that the paper-plastic aluminum composite material used in the composite carton and the AL composite plastic flexible packaging film used in the milk powder packaging are the best barrier properties in various dairy packaging materials, and the breathable and moisture-permeable data are in the high barrier range. Of course, the corresponding cost is also very high. According to the relevant information, the cost of a Tetra Pak package is not less than 0.5 yuan. The coating/composite packaging film used in aseptic packaging is next to the medium barrier and the cost is moderate. The most common PE black and white film in the package and the milk film have the worst barrier properties. Only the air permeability data is several thousand times higher than the paper plastic aluminum composite and the AL composite plastic flexible packaging film. The film is several hundred times higher, of course, the price is also the lowest, often less than 0.1 yuan.
The choice of packaging materials and the choice of material structure and barrier properties are all based on the product's predetermined shelf life. For example, paper-plastic aluminum composite materials with high barrier properties and dairy or dairy products packaged with AL composite plastic flexible packaging film often have a shelf life of several months, and the storage environment is not very high, basically no need to be in a refrigerated environment. Under the preservation, if the material with low barrier property is likely to cause a large number of products to deteriorate in advance, or bring more difficulties to transportation and storage. The shelf life of dairy products in black and white film packaging is only a few days. This product is often consumed in large quantities and belongs to the type of fast-distribution and quick-selling. If the packaging materials used are too good (for example, materials with medium barrier), the shelf life will not be given. The obvious extension will increase the packaging cost of the product, so 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 barrier material is designed according to the requirements and the corresponding materials are selected. It can be seen from the data in the table that the same paper-plastic aluminum composite material, but the gas barrier property of the 2# sample is not as good as the 1# sample, and the moisture resistance is better: the same as the PE film, but some barrier properties are more than 900 And some will reach more than 1,300. The increase in barrier properties is based on the premise of increasing costs, so as long as the packaging material can guarantee the quality of the product in the shelf life, the one-sided pursuit of barrier properties does not have much benefit.
3. Summary At present, China's domestic dairy packaging materials can meet the general quality requirements (combined material barrier, light protection, mechanical properties and sealing performance), but still need to rely on imports in high-end dairy packaging. However, with the continuous introduction of new products in the dairy industry and the promotion of new treatment processes, the development of new packaging forms and the use of packaging materials have entered a period of rapid development. However, the choice of materials is higher, only for materials. All the performances are thoroughly tested to better ensure the quality of dairy products and ensure the safety of consumers.