Modified atmosphere packaging, also known as Nitrogen injection packaging, gas filling packaging, changes the gas composition around the food to keep it relatively stable for a certain period of time, and uses this ideal hydrogen gas environment to inhibit the growth of microorganisms and prolong the shelf life of food to achieve the purpose of food preservation.
In the global market, the use of modified atmosphere packaging of food has developed rapidly, and is gradually replacing the traditional food vacuum packaging. Vacuum packaging needs high temperature sterilization, although it can maintain the quality of products for very long time, but it damages the taste, color and other aspects of foods. The global consumption of meat is large, and meat products are prone to corruption and short shelf life. Therefore, it is urgent to strengthen the research of meat preservation technology. Modified atmosphere packaging technology of meat can ensure its natural flavor, reduce juice loss and color change, and improve meat quality.
1. Fresh-keeping mechanism of modified atmosphere packaging
The main characteristics of modified atmosphere packaging are that after packaging with suitable permeable materials, the air around food will be replaced by the gas needed to actively regulate the gas environment during meat storage, so as to inhibit the growth and reproduction of microorganisms, inhibit the oxidative rancidity of fat and slow down the oxidative discoloration of myoglobin. The gases used in modified atmosphere packaging are mainly oxygen, carbon dioxide, nitrogen, and trace gases such as carbon monoxide, nitrous oxide, acetylene oxide and sulfur dioxide. Modified atmosphere packaging generally uses two or four kinds of gases to adjust their content ratio to meet the needs of different meat products. The contents of various gases in meat products are shown in Table below.
2. Main role of gas in modified atmosphere packaging
The commonly used protective gases in modified atmosphere packaging are CO2 (carbon dioxide), O2 (oxygen) and N2 (nitrogen). Their respective functions are described as follows:
(1) CO2 is a bacteriostatic gas that inhibits the growth and reproduction of bacteria. Its characteristics are as follows: a. The best bacteriostasis occurs in the lagging stage of the bacterial reproduction curve (the bacteriostasis index is less than 100/100g); B. It is easy to dissolve in water and fat at low temperature; C. It has bacteriostasis effect on most aerobic bacteria, but it is ineffective for anaerobic bacteria and yeast; D. The lowest concentration of bacteriostasis usually occurs. 30%.
(2) O2: its functions include three aspects: A, inhibiting the growth and propagation of anaerobic bacteria; B, keeping the red color of fresh pigs, cows and mutton; C, maintaining fresh fruits and vegetables, metabolism and aerobic respiration.
(3) N2: Inert gas, which does not work with food, is only used as filling gas of mixed gas.
Modified atmosphere packaging with oxygen has a good effect, which is mainly related to the role of oxygen in promoting the production and maintenance of myoglobin and inhibiting the growth of anaerobic bacteria in the process. It can also provide the oxygen needed for metabolism, thus maintaining the natural color of meat. However, the presence of oxygen can promote the growth of aerobic microorganisms, so carbon dioxide and nitrogen are widely used in industrial applications.
Carbon dioxide has obvious inhibitory effect on aerobic bacteria. Its principle is that it can change the permeability of cell wall and the pH value of environment and inhibit bacterial reproduction and enzyme activity, but it has poor inhibitory effect on yeast and lactic acid bacteria. Excessive concentration of carbon dioxide will affect the flavor of food and may cause the collapse of packaging boxes. Nitrogen, as an inert gas, does not participate in the reaction in modified atmosphere packaging, and mainly plays the role of filling and preventing parasitic pests. Carbon monoxide can stabilize hemoglobin to maintain meat color, inhibit autolysis and prevent lipid oxidation during meat preservation.
3. Key Technological Points of Modified Atmosphere Packaging
3.1 Quality Control of Chilled Meat
Studies have shown that the number of microorganisms in the muscle tissue of living animals is very small. Most of the microbial contamination of muscle tissue occurs after slaughter. Although chilled meat is under low temperature control (0-4 ℃), there are still some bacteria on the meat, such as Pseudomonas aeruginosa and Achrobacter aeruginosa, which are caused by low temperature. Low temperature can only inhibit the growth and reproduction of some thermophilic bacteria, and anaerobic Lactobacillus can also multiply in high CO concentration packaging. Therefore, it is necessary to strengthen the total control of bacteria in chilled meat before packaging, and control the quality of filling and sealing during packaging, so as to reduce all kinds of pollution in packaging process.
3.2 Selection of Packaging Materials
Modified atmosphere packaging should choose good barrier packaging materials to prevent gas escaping from packaging, but also to prevent the infiltration of oxygen in the atmosphere, in order to maintain the components of protective gases in packaging.
In addition, all packaging materials must have enough mechanical strength to withstand the change of pressure during vacuum pumping, and also require a certain stiffness of the material so that the packaging bag can automatically open and inflate. In addition, the choice of packaging materials should also consider the economic practicability, not too much to increase the burden of consumers on the basis of aesthetic and practical. If shelf life does not need to be long, the general barrier PA/PE or PET/PE can be satisfied; if shelf life requires long, it is best to use high barrier polyvinylidene chloride (PVDC) or ethylene-vinyl alcohol (EVON) composite packaging materials.
At present, PVDC high barrier materials are widely used. Recently, France has introduced to the market a double-layer superimposed film specially for meat packaging. Its outer layer is a high density polyethylene film with special structure and properties. Its inner layer is edible paper. The superimposed double-layer film is translucent with a thickness of only 12 mm, but with good strength, safety and non-toxicity, it can directly contact with meat products. Meat products can be packed with this film. It can solve the problem that common packaging material meat will soak bleeding and oil, and it is not easy to separate from the meat and make the surface hard, and can maintain the original color and fragrance of meat. American experts have adopted new technology to make plastic packaging materials with CO2. That is to say, using special catalysts, CO2 and ethylene oxide (or propylene oxide) are mixed equally to make new plastic packaging materials, which are characterized by glass-like transparency and airtight, similar to polycarbonate and polyamide resins, and will not be completely decomposed into gases at 240℃. These new packaging materials will inevitably be widely utilized in the Cooled meat modified atmosphere packaging.
4. Contrast of cost between modified atmosphere packaging and vacuum packaging
Modified Atmosphere Packaging and Vacuum Packaging Material Requirements are similar. The increased cost of Modified Atmosphere Packaging is mainly gas cost. Gas cost calculation: Among the three gases, carbon dioxide price is the highest, the gas pressure of each carbon dioxide high-pressure cylinder is 13-15 MPa, the solvent of cylinder is about 40 liters, the weight of gas is about 10 kg, and the inflation price is 30 yuan/bottle. 。 For example, the mixed gases are all calculated by carbon dioxide. Each liter of gas consumed is 0.1 MPa. Its weight is about 3g, and its cost is (30/10*1000)*3=0.009 yuan/liter. That is to say, the cost is less than one penny per liter of gas with a pressure of 0.1 MPa.
5. Effect of Modified Atmosphere Packaging on Shelf Life
In 2010, limbo et al. established a dynamic model to study the minimum fiber diameter, muscle fiber tensile index and sarcomere length of freshly minced buffalo beef, which could be stored for 9 days at 4.3 ~8.1 ~C in modified atmosphere packaging. Vacuum packaging could aging meat quality. Modified atmosphere packaging could make meat juice stored for 3-4 days and for 2 days at 15.5 ~C. 。 In 2006, seydim et al. studied the storage of fresh ostrich meat in high oxygen, high nitrogen, vacuum and air at about 4 C. It was found that oxygen was the limiting factor for the shelf life of ostrich meat. In 2003, Murcia et al. studied the stability of components and shelf life of ready-to-eat food in vacuum packaging or modified atmosphere packaging. It was found that vacuum packaging or modified atmosphere packaging was very effective for prolonging shelf life of food to 29 days, and the change value of composition of food was the smallest.
6. Effect of Modified Atmosphere Packaging and Other Methods on Meat Storage
The method of combining chemical substances and modified atmosphere packaging was used to study a better synergistic method for meat storage. In 2005, masniyon et al. studied the effects of phosphate compounds combined with modified atmosphere packaging on perch slices.The results showed that phosphate compounds pretreatment could reduce the number of microorganisms, total volatile substances and trimethylamine.
In 2009, Lu studied the effects of different fungicides and modified atmosphere packaging on Penaeus chinensis. The results showed that the count of aerobic plate reached 107 cfu/g after 13 days of storage, while that of control group exceeded 107 cfu/g on the ninth day. The shelf life of shrimp soaked in fungicide compound was 13 days and 17 days respectively when 40% CO 2, 30% O 2, 30% N 2 or 100% CO 2 were used in modified atmosphere packaging.
In 2005, Lauzurica et al. studied the effect of supplementation of vitamin E in feed on the storage of modified atmosphere packaged mutton. During storage, meat fat and color oxidation increased significantly, especially in lambs without supplementation of vitamin E, while supplementation of vitamin E in feed prolonged CAP for 14 days.
In 2009, Suman et al. found that the combination of increasing lactic acid content and CO atmosphere to make steak muscle cooperate with each other in meat preservation is still the main research direction in the future. Meat pre-ripening reaches the minimum value and keeps beef color stable.
In 2009, Economou et al. found that the shelf life of fresh meat stored in modified atmosphere packaging after nisin and EDTA treatment increased significantly. With the increase of nisin and EDTA treatment, the storage time of fresh meat samples increased correspondingly, reaching 20 days.
7. Application of Modified Atmosphere Packaging in Preservation of Different Meat Products
7.1 Application of Modified Atmosphere Packaging Technology in Fresh Meat
Fresh meat can be classified into two categories: one is pig, sheep and beef, the other is red meat, which is called red meat packaging. It requires both fresh meat color and preservation. Another kind of poultry meat, such as chicken and duck, can be called white meat packaging, which only requires preservation. Red meat contains bright red oxymyoglobin, which can keep the flesh bright red under hyperoxia environment and reduce to light purple myoglobin under hypoxia environment.
Traditional vacuum packaged red meat, due to hypoxic meat is light purple, will be mistaken by consumers as not fresh and nutritious sales. The protective gas of modified atmosphere fresh-keeping packaging of red meat is composed of O2 and CO2. The concentration of O2 needs to be more than 60% to maintain the red color of meat. The lowest concentration of CO2 is not less than 25% to effectively inhibit the reproduction of bacteria. Different kinds of red meat have different myoglobin content and red degree. For example, beef is darker than pork. Therefore, oxygen concentration in different red meat modified atmosphere packaging needs to be adjusted to achieve the best color and preservation effect. The composition of protective gases in modified atmosphere fresh-keeping packaging of pork is usually 60-70% O2 and 40-30% CO2, and the shelf life at 0-4 C is usually 7-10 days. Modified atmosphere fresh-keeping packaging of poultry meat aims at preservation. The protective gas is composed of CO2 and N2. Poultry meat is packaged with 50% – 70% CO2 and 50% – 30% N2 mixture. The shelf life of modified atmosphere fresh-keeping packaging is about 14 days at 0 – 4℃.
7.2 Application of Modified Atmosphere Preservation Packaging in Cooked Meat Products
In addition to strict requirements for raw materials, it is important for cooked meat to meet pasteurization standards and maintain time. For example, the pasteurization standard of cooked beef packaged by USDA requires that the central temperature of the food should reach 71℃ and be maintained for 7.3 seconds. Cooked food needs to be quickly cooled by vacuum immediately after cooking and packaged after slicing. If the hygienic conditions at this stage are poor, such as pathogenic bacteria in the air, inadequate disinfection of cutters and operators, food will be contaminated again. It is difficult for residual bacteria to prolong shelf life by keeping fresh in the atmosphere.
Modified atmosphere packaging of cooked food relies on carbon dioxide to inhibit the growth and reproduction of most aerobic bacteria and fungi, while the most effective inhibition of carbon dioxide is very low (about 100-200/g). Therefore, the less bacterial contamination before packaging of cooked food, the better the inhibition effect of modified atmosphere fresh-keeping packaging, and the longer shelf life. Generally, the shelf life of refrigerated display containers in supermarkets can reach 40-60 days with 20%-35% CO2 and 75%-35% N2 air-conditioned MAP modified atmosphere packaging by rapid vacuum cooling.
8. Packaging machines for MAP modified atmosphere packaging
By automation grade, there are 3 types of meat MAP modified atmosphere packaging machines: Semi-auto tray sealer machine with MAP function, Inline tray sealing machine with MAP function, Thermoforming packaging machine with MAP function, please visit SHANDONG KANGBIETE PACKAGING website for machine details.