In the process of meat production and processing, there are always two kinds of cooked technology, namely high temperature and high pressure sterilization and low temperature and pressure sterilization. Low-temperature sterilization of meat foods due to the low heating temperature, the meat fiber is not destroyed, so the mouth feel fresh, a variety of nutrients preserved; but because it only kills pathogenic bacteria, there are still a large number of spoilage bacteria, not only short shelf life, And it is very easy to cause loss in the circulation field. The high-temperature pasteurized meat foods cause excessive shrinkage of the fibers of the meat due to the high heating temperature and the taste is inferior to the low-temperature sterilization products. However, because it kills all the bacteria, the internal causes of spoilage are eliminated, and the shelf life can be greatly extended.
High-temperature sterilization of meat foods such as the use of high barrier packaging materials, not only at room temperature storage shelf life is longer, but also transport, storage, sales are very convenient, very suitable for modern consumer needs. Therefore, it is an important product development direction of the meat food industry to vigorously develop the production of shelf-stable meat products at room temperature. The packaging industry is following this trend, making a difference and making innovations. It can meet the needs of the food industry, and it can also win a broad market for itself.
It is understood that the earliest packaging that can store meat foods at room temperature is cans. It is a tin can made of tinplate, and later uses glass bottles for packaging. Both tinplates and glass bottles are resistant to high temperature cooking and high barrier properties, so the shelf life of canned foods can reach more than 2 years. However, because tinplate cans and glass bottles are rigid packaging containers, and the volume and weight are heavy, the chemical resistance of tinplate is not good, and metal ions are easily precipitated during the loading of acidic foods, which affects the flavor of food.
In the 1960s, the United States invented aluminum-plastic composite membranes to solve the packaging of aerospace foods. It used it to package meat foods, and was stored at room temperature through high-temperature and high-pressure sterilization. The shelf life was as long as more than one year. Aluminum-plastic composite film is similar to canned box, soft and light, so named soft cans. At present, meat products with a longer shelf life are stored at room temperature. If a hard-packed container is used, tinplate cans and glass bottles are used. If soft packaging is used, almost all aluminum-plastic composite films are used.
The aluminum-plastic composite film is a laminated composite multilayer film, which is generally three layers. The typical structure is a surface layer/adhesive/aluminum foil/adhesive/heat seal layer (CPP). The packaging film has the advantages of beautiful appearance, good mechanical properties, high barrier properties, high temperature cooking resistance and excellent hygienic properties, and is lightweight and soft, and thus is widely used for packaging various foods. However, there are also some drawbacks, such as the hard and brittle nature of the aluminum foil, and its poor flexibility compared to plastic films.
In order to prolong the shelf life of meat foods, high-temperature cooked meat foods are packed in vacuum packaging. When the aluminum foil composite material is vacuumed, since the flexibility of the aluminum foil is not enough, it is difficult to completely adhere to the contents, and the air in the packaging bag is likely to be unclean, which affects the preservation of the food. Therefore, when using aluminum foil for meat packaging, the thickness should not be too high. However, because the barrier property depends on the thickness and the processing level, when the thickness is small, a large number of pinholes easily occur. Therefore, for the packaging of meat foods that are resistant to storage, the thickness of the aluminum foil can not be too thin; if the aluminum foil is too thin, the aluminum foil is too thin. Composite membranes will also form a lot of wrinkles after evacuation, which in turn will cause cracks and loss of barrier properties. Therefore, the thickness, barrier property and flexibility of aluminum foil are always the three contradictions that plagued the application of aluminum foil composite film.
From the market point of view, due to the opacity of aluminum foil composite film-packed foods, consumers cannot see the color and shape of the contents, which is detrimental to consumers' purchase. In addition, some manufacturers use the aluminum-plastic composite film to opaque the defects of the products and even deceive them. , harm consumers. Therefore, most consumers choose completely transparent packaging instead of opaque aluminum-plastic composite film packaging, resulting in poor sales of this packaged food. Aluminum-plastic composite packaging cannot be heated by microwaves, and is more expensive than plastic film. All these have affected the application of aluminum-plastic composite films. Therefore, the food processing industry has always hoped that the packaging material process can provide a barrier property similar to that of the aluminum-plastic composite film, but the packaging material that is both transparent and resistant to high temperature cooking replaces the aluminum-plastic composite film.
Among the plastics currently used in industrial applications, only PVDC plastic films have both high barrier properties and high-temperature retort resistance similar to aluminum foils. For a long time, people hope to use PVDC plastic as an intermediate layer to make a composite film, which will become transparent and resistant to high temperature cooking, and it also has a high-barrier high-temperature cooking food packaging film similar to aluminum foil. However, PVDC plastic is a unique and extremely difficult-to-process plastic. There are many difficulties in using it as a middle layer to make composite films.
PVDC plastic film was manufactured in 1938 by a special blown film process invented by scientists of Dow Chemical Company. Enclosures for meat enema that have been used for high-temperature cooking since the 1950s have been stored at room temperature with a pasteurized meat product packaged in it, with a shelf life of more than 6 months. However, PVDC films can only be heat-sealed with high-frequency dielectric heating and cannot be heat-sealed by the commonly used resistance heating method. Therefore, PVDC films have only been used as casings for many years and cannot be used as packaging bags.
In recent years, experimental studies have shown that using a solvent-free composite method, the PVDC film can be directly compounded into a composite film without any treatment. This kind of composite film will not be destroyed in the form of the whole film when cooking at high temperature, and it will remain flat and smooth all the time, and it will be closely combined and integrated to meet the needs of high-temperature cooking food packaging. After being put on the market, the PVDC laminated composite high-temperature cooking food packaging film made by this method has been affirmed by experts, and proved that it is a high-transparency, high-barrier, and high-temperature-resisting cooking material after the aluminum-plastic composite film. Food packaging film, performance indicators have reached the international advanced level.
Compared with aluminum-plastic composite film, PVDC laminated composite film has similar barrier properties, is completely transparent and more flexible, and is used for vacuum food packaging of meat food. The air in the bag is very clean, which is more conducive to the preservation of meat food, and can be microwaved. Heating, and the price is only equivalent to 70% to 80% of aluminum foil composite film, so it can replace aluminum plastic composite film applications in a considerable range.
At present, the research and development of barrier films coated with poly(vinyl alcohol) (PVA) type BOPP have brought new hopes for food packaging. This type of barrier film has both oxygen barrier permeability and water vapor barrier properties. The polymer contains no toxic elements and no toxic element transfer occurs during use. The barrier material PVA is a microbial synthetic polymer material with hydrolysis and biological properties. Degradation dual degradation mechanism, can be completely degraded into water and carbon dioxide, is a high-performance environmentally friendly material, can replace PVDC coating film in many ways. It is mainly used for the packaging of meat foods, quick-frozen convenience foods, and non-food-based fragrant types (such as insect repellent), and has a broad application prospect.
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