Research Progress on packaging technology of the h

Research progress of chilled meat packaging technology

chilled meat refers to fresh meat that rapidly cools the carcass of livestock and poultry slaughtered after strict implementation of the quarantine system, so that the carcass temperature (the rear leg is the measuring point) is reduced to 0 ℃ - 4 ℃ within 24 hours, and remains within the range of 0 ℃ - 4 ℃ in the subsequent processing, circulation and retail process. Because the chilled meat is always under cooling conditions and has experienced a full post ripening process, compared with hot fresh meat and frozen meat, the chilled meat has the characteristics of less juice loss, soft and elastic texture, delicious taste and high nutritional value, so it is widely welcomed by consumers. Developed countries began production and promotion in the 1920s and 1930s. At present, more than 90% of the raw meat consumed is chilled meat. China's meat output ranks first in the world, but chilled meat will be the inevitable trend of fresh meat development. Extending the shelf life of chilled meat is very important for the development of chilled meat

spoilage of chilled meat

the spoilage of meat is the continuation of the meat maturation process, which is due to the fact that the meat contains a considerable amount of glycogen and the accelerated glycolysis of animals after death. In the process of glycolysis, the decrease of pH value of meat is unfavorable to the growth of spoilage bacteria in meat, which temporarily inhibits the progress of spoilage. The blood and muscle of healthy animals are usually sterile, and the corruption of meat is actually caused by the reproduction of externally infected microorganisms on the surface. Many microorganisms can not act on proteins, but can act on free amino acids and low peptides. They can oxidize and dehydrogenate amino acids to produce ammonia and corresponding ketoacids. At the same time of meat maturation, protein autolysis produces small molecules of amino acids, which have become essential nutrients for microbial growth and reproduction. When microorganisms propagate to a certain extent, they secrete protease, decompose protein, produce low molecular components, and promote the proliferation of various microorganisms, so the meat is corrupt. In addition to a series of changes in protein and fat, the appearance of meat also changes significantly. The color changes from bright red and dark red to dark brown or even dark green. It loses luster and looks dirty, the surface is sticky, and it will produce corruption odor and even mildew. Rotten meat completely loses the value of processing and eating

I. microbial corruption. When slaughtering animals, most fresh meat will be indirectly or directly contaminated by spoilage bacteria. In addition, animal carcasses can also be contaminated with bacteria during processing and segmentation. Putrefactive bacteria contaminate the surface of fresh meat. Most fresh meat is sterile in the deep layer before it begins to decay. Because a large number of spoilage bacteria are attached to the surface of meat, they have little effect on deep meat. The time of microbial spoilage depends largely on the degree of product contamination and storage temperature before storage. Spoilage psychrophilic bacteria often found in chilled meat include Pseudomonas, Moraxella, Acinetobacter, Aeromonas, enterobacter, Staphylococcus, Lactobacillus, and cyclomycetes thermodead. The pathogenic bacteria often found in chilled meat are: enterocolitis, but the fatigue test machine is just the opposite. Yersinia, Clostridium botulinum, Clostridium perfringens, Salmonella, Staphylococcus aureus, Campylobacter, etc

II. Color deterioration. Color is the first impression to consumers. Protecting the color of chilled meat is very important for meat sales. The color of fresh meat muscle tissue depends on the oxidation state of muscle pigment and myoglobin. The function of myoglobin is to deliver oxygen to muscle tissue. The Japanese body of myoglobin is purplish red. It can combine with oxygen to produce oxygenated myoglobin, which is bright red and a symbol of fresh meat; Myoglobin and oxygenated myoglobin can be oxidized to produce ferritin red eggs, which are brown and darken the meat; In the presence of sulfide, myoglobin can also be oxidized to thiomyoglobin, which is green and heterochromatic. The formation or transformation of oxymyoglobin and ferrimyoglobin is the most important for the color of meat. Because the former is bright red, which means that the meat is fresh and loved by consumers, and the latter is brown, how to choose a reassuring information pulling machine when placing the meat? The data tension machine can test the long-term symbols of tension, contraction, zigzag, shearing, peeling, tearing, two-point extension (with extension meter) of various metal and non-metallic materials. When ferrimyoglobin ≤ 20%, the meat color is still bright red; When it reaches 30%, the meat shows a slightly darker color; At 50%, the meat is reddish brown; When it reaches 70%, the meat turns brown, so preventing and reducing the formation of ferrimyoglobin is the key to maintaining meat color. If no measures are taken, the general color of meat will undergo two changes: the first is from purple to bright red, and the second is from bright red to brown. The first change takes place within 30min after the meat is placed in the air; The second change is a few hours for those who are fast and a few days for those who are slow. The speed of transformation is affected by many factors such as air pressure, pH, bacterial reproduction degree and temperature in the environment. Slowing down the second change, that is, from bright red to brown, is the key to maintaining the color of fresh meat

third, non microbial tissue deterioration. Many enterprises have not paid enough attention to the tissue deterioration caused by non microbial activities during the packaging and storage of fresh meat. In fact, accelerated acid excretion of muscle tissue during storage is an unwanted tissue change. The acid excretion process of muscle includes the gradual deterioration of protein. This will lead to the loss of muscle fiber, so that the meat has an unpopular taste. When proteins are destroyed, they release peptides and free amino acids. This peptide makes meat have a liver like flavor, which will be suspected by consumers when a meat product does not often have this flavor. When the tyrosine concentration increases, the meat has a bitter taste. Tyrosine is insoluble in water and crystallizes at low concentrations. At present, the building energy consumption accounts for more than 27% of the total energy consumption in China, and tyrosine crystals can be seen on the surface of meat. This kind of crystal will be mistaken for microbial flora, making the appearance of meat unacceptable to consumers. In addition, the smell and flavor changes caused by oxidative deterioration of meat may also occur in some form of meat packaging

fresh keeping packaging technology of chilled meat

the main reasons for meat spoilage are microbial reproduction, enzyme action and oxidation. In theory, the storage and preservation of meat is to adopt good hygienic operation norms in slaughtering and processing to prevent microbial pollution as much as possible. Appropriate packaging and preservation methods should be adopted to eliminate or delay the process of these effects

packaging technology is widely used in fresh meat preservation. The main functions of packaging are: inhibiting microbial growth and preventing secondary pollution; Slow down the speed of fat oxidation; Make meat products tidy and improve competitiveness

I. vacuum packaging (VP). Vacuum packaging reduces the oxygen content by pumping out the air in the package, and keeps the myoglobin in the meat in the reduced Lavender state, but when the meat is taken out of the bag and exposed to oxygen, it can quickly return to bright red; Prevent the contamination caused by the contact between meat and the outside world, and ensure the hygiene of products; The high barrier membrane prevents the weight loss caused by dehydration on the meat surface; Inhibiting the growth and reproduction of aerobic bacteria has relatively prolonged the shelf life of meat. There are three forms of vacuum packaging for fresh meat abroad, with a shelf life of up to 21 days: (1) the segmented beef and pork pieces are packed in shrink film bags, then vacuumized and heat sealed, and then hot water is used to shrink the bags; (2) It is packed with thermoforming vacuum packaging machine and high barrier plastic film. Put a single piece of beef or pork into a thermoformed plastic box, and then cover it with a film to vacuum and heat seal; (3) Vacuum body fitted packaging has been widely used in Europe. At present, there are domestic research on the combination of vacuum packaging and preservative, so that they can give full play to their respective advantages and have good fresh-keeping effect

II. Modified atmosphere packaging (map or cap). Modified atmosphere packaging is to put fresh meat in the package, remove the air, and replace the gas environment in the package with the selected gas, so as to inhibit the growth of microorganisms and prolong the shelf life of fresh meat. The commonly used gases in modified atmosphere packaging are: (1) CO2 inhibits the growth of bacteria and fungi, especially in the early stage of bacterial reproduction, and can also inhibit the activity of enzymes. Aerobic bacteria such as mold, trichomonas aeruginosa and Achromobacter are highly sensitive to CO2 and are inhibited. CO2 has little inhibitory effect on yeast and no inhibitory effect on anaerobic bacteria such as lactic acid bacteria. Studies have shown that lamb packaged with 100% CO2 modified atmosphere can significantly prolong the storage period, significantly inhibit Pseudomonas, and lactic acid bacteria become the dominant bacteria. (2) The function of CO2 is to maintain oxygenated myoglobin, make the meat colorful, and inhibit the growth of anaerobic bacteria, but also create a good environment for many harmful bacteria; (3) N2 is an inert filling gas, which does not affect the color of meat, can prevent oxidative rancidity, mold growth and parasitic pests, and prevent package collapse caused by a large amount of CO2 dissolved in meat

the preservation effect varies with the proportion of mixed gas in meat preservation, which is usually divided into high oxygen packaging and low oxygen packaging. High oxygen conditioning packaging can maintain a good red color. In high oxygen conditioning packaging, when the concentration of CO2 is less than 20%, aerobic bacteria can reproduce slowly; When CO2 concentration exceeds 20%, bacterial reproduction can be halved; However, when the concentration of CO2 is higher than 25%, there is water-soluble protein precipitation, which makes the meat brown. Therefore, in high oxygen conditioning packaging, the concentration of CO2 is generally between 20% and 25%, the concentration of O2 is greater than 60%, and the rest is N2; The purpose of hypoxic modified atmosphere packaging is to exert the antibacterial effect of CO2, but it can not maintain the color of fresh meat. The proportion of mixed gas in hypoxic modified atmosphere packaging is wide, with CO2 ranging from 50% to 90%, N2 ranging from 10% to 40%, and O2 proportion ranging from 1% to 10%. High oxygen tone packaging is used for retail small packaging, while low oxygen tone packaging is used for large packaging of fresh meat. The fresh-keeping experiment of pork was carried out under the cooling condition of 0 ℃ - 4 ℃ with different packaging methods such as air, vacuum and modified atmosphere. The results showed that the fresh-keeping effect of o270%, co230% and o250%, CO250% modified atmosphere packaging pork was better than vacuum packaging and air packaging, and the shelf life could be extended by 6 days

some studies have added CO to modified atmosphere packaging and used CO to combine with myoglobin to form carbon monoxide myoglobin (MbCO), which is more stable than oxygenated myoglobin (MbO2), so that the chilled meat has a bright red color. Foreign studies have shown that the preservation effect of modified atmosphere packaging with 1% CO is better than that of vacuum and other modified atmosphere packaging without Co. Some domestic experts have studied the different packaging forms of chilled pork. The experimental results show that the group containing CO is an ideal method for the preservation of chilled pork at present. During the 21 day storage process, not only the TVB value and TBA value are low, the red is stable, and there is no peculiar smell, which can inhibit the growth of spoilage bacteria. In addition to the weak inhibition of lactic acid bacteria, it has a weak inhibition effect on Pseudomonas Enterobacteriaceae and heat dead cyclomycetes have strong inhibitory effects, and their inhibitory effects on spoilage bacteria are significantly better than those of vacuum packaging group and oxygen containing packaging group

as chilled meat has increasingly become the mainstream of meat consumption, packaging and sales of chilled meat has become an imperative development trend. Reasonable and effective packaging will be more and more widely developed in the production, circulation and sales of chilled meat

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