1, the characteristics of cold meat
Cold meat refers to the rapid cooling of the carcass after slaughter, so that the temperature of the carcass is reduced to 0-4 °C within 24 hours, and it is kept fresh in this temperature range during subsequent processing, circulation and sales. meat. Compared with hot fresh meat, cold meat is always in a cooling environment, and most of the microbial growth and reproduction is inhibited, which ensures the health and safety of the meat. Compared with frozen meat, cold meat has less juice loss, softness and elasticity. The advantages of delicious taste and high nutritional value.
However, cold meat is sold in a freezer at 0 to 4 ° C. The temperature can only inhibit the growth and enzyme activity of the microorganisms and the activity of the enzyme to a certain extent, and cannot terminate its activity. For 3-4 days, the quality and safety of fresh meat still exists. How to extend the shelf life of chilled meat has become an urgent problem to be solved in the chilled meat processing industry. The use of reasonable and effective fresh-keeping technology is an indispensable part of ensuring high-quality cold meat. At present, the advanced cold fresh meat packaging technology mainly includes vacuum shrink packaging, thermoforming packaging, vacuum body packaging, and atmosphere fresh-keeping packaging.
2, advanced cold fresh meat preservation packaging technology
2.1 Vacuum shrink packaging
Vacuum shrink packaging has been widely used in developed countries, with the United States being the world's largest shrinking bag consumer market; Australia, New Zealand and Europe also have large markets, and Asia is relatively small in terms of consumer market. The overall market size of shrink bags is between 10 and 15 billion bags or between $1 and $2 billion.
When the vacuum shrink bag is used for cold meat packaging, the inner bag is vacuum sealed and placed in hot water or hot aisle. The plastic bag shrinks into the original shape of the meat piece and becomes the “second layer skin†of the meat (Fig. 1). . Shrinkage reduces excess material outside the package, making the package more compact, more aesthetically pleasing, and increasing the attractiveness of meat sales; shrinkage eliminates wrinkles in the bag and the capillary water absorption caused by it, thereby minimizing blood and water from the meat. Exudation. Based on the shrinkage action, the thickness of the barrier plastic bag film is thus increased, enhancing its wear resistance and barrier properties. Through vacuum shrink packaging, cold meat can be shelfd for up to one month after slaughter.
The shrink film is prepared by co-extrusion by double-bubble method, and the raw material resin is melt-extruded through the extruder to extrude the first bubble, and the extruded film tube is rapidly cooled by a vacuum-fixed neck cage, and then flattened by a herringbone plate and a pulling roller. Traction; the dried and flattened material is irradiated into the pre-hot water tank after being irradiated by the EB device, and is formed into a second bubble by secondary inflation, and finally drawn to form a film. The product shrinkage rate is about 35 to 45%, and the thickness ranges from 50 to 90 μm. The heat shrinkable bag made of film is generally tubular, and the seal of the shrink bag is different from the straight seal of the vacuum bag, which is a circular arc seal, so that the shrinkage of the bag is contracted to the maximum extent after the heat shrinkage. Leave no scrap leftovers.
2.2 Thermoformed packagingIn the early 1990s, the world's leading functional packaging materials such as Cryovac, Curwood, and Wipak took the lead in entering the market with brand and technology advantages, and dug the first barrel of gold. In China, thermoforming packaging materials have been cultivated for more than ten years, and the market scale has developed rapidly. The main processes used in thermoforming packaging materials are casting processing and downward extrusion water cooling processing. The casting processing technology is relatively mature, but the cooling efficiency is low, the appearance is striped, and the yield is low; and the downward extrusion water cooling processing technology It has the advantages of high tensile strength, high production efficiency, soft and transparent film formation, and is a high-tech that has developed rapidly in recent years. It will also be the mainstream technology for future production and development.
Film thermoforming is a property in which the film produced by the above process can be softened again by heating. By means of the pressure difference between the two sides of the film or the mechanical pressure of one side, the film is formed into a packaging container of a desired shape by using a suitable mold. Thermoformed packaging has the following advantages: excellent molding performance, high transparency, safe and hygienic circulation, high degree of automation, and production capacity is several times higher than manual packaging.
2.3 Vacuum body packaging
Vacuum body packaging [2] is a novel commodity packaging technology widely used in the international food packaging industry, mainly for fresh meat, fish, aquatic products, cooked meat products, salted products, sliced ​​sausages and sushi. Packaging, these foods not only have good display properties after being packaged, but also have a long shelf life and are convenient to eat.
The vacuum body package is mainly composed of a substrate tray and a plastic cover film (Fig. 4). The process of the body packaging is as follows: the packaged product is placed in the tray, so that the special plastic cover film covering the product is pressed against the surface of the product under heating and vacuuming, and sealed with the substrate tray. The substrate tray for vacuum body packaging requires the characteristics of good tensile properties, good barrier properties, high strength, and high pressure resistance. The structure is generally high barrier PVC or PET composite sheet, such as PVC/PE/EVOH/PE, VMPET/PE/EVOH/PE, etc.; the plastic cover film is generally a multi-layer high-barrier co-extruded material heated to a viscous flow state, and the inner layer is a hot-adhesive and elastic-sl. Surlyn and EVA resin. Different from stretch-molded packaging, vacuum body packaging does not require any mold. It can achieve the effect of close to food and sealed packaging through special transparent body cover film for different sizes and shapes. It is convenient, economical and efficient. . Â Â Â
2.4 modified atmosphere packaging
Modified atmosphere preservation [3] is to package food with packaging materials with gas barrier properties, according to the actual needs of customers, a certain proportion of O2+CO2+N2, N2+CO2, O2 + CO2 mixed gas is filled into the package, thereby inhibiting microorganisms The growth and reproduction, extending the shelf life, thereby extending the shelf life of food and increasing the value of food (Figure 5). CO2 mainly inhibits the growth of bacteria and fungi, especially in the early stage of bacterial growth, and has the best antibacterial effect at low temperature and 20%-30% concentration; N2 mainly prevents oxidative rancidity and inhibits mold growth; O2 main oxygenated muscle red The protein keeps the meat in a bright red color and inhibits the growth of anaerobic bacteria.Whether the chilled meat can be adjusted to maintain the initial atmosphere during a certain period of time depends largely on the choice of packaging materials used. Therefore, the selection of packaging materials is also a key link. The following is the selection package. Materials should pay attention to the problem:
1) According to the fresh-keeping requirements of cold meat, it is required to use a film and a box with low gas permeability or high barrier property. Thereby reducing the gas in the package to be replaced by the gas in the atmosphere through the film;
2) The cover film should have anti-fog property and high light transmittance. If the anti-fog and high light transmittance of the cover film will damage the aesthetics of the product and affect sales.