Modified atmosphere packaging of fresh meat is a technology that replaces the air in the packaging container with a protective gas suitable for freshness, inhibits the proliferation of bacteria, and combines the regulation of temperature to achieve long-term preservation and freshness.
Development of fresh meat packing – modified atmosphere packaging technology
CO2 is the most commonly used gas in modified atmosphere packaging and storage of fresh meat. The first application of high-concentration CO2 modified atmosphere on meat preservation was in 1930. It played a good role in keeping fresh meat on ships that transported fresh meat from Australia and New Zealand to Britain. By 1938, 26% of Australia’s fresh meat and 60% of New Zealand’s fresh meat were transported under controlled atmosphere with CO2 . The gas ratio is CO2:O2 = 20: 80 (volume ratio), which is generally used in large packages or large containers to store fresh meat.
In the 1970s, the fresh-keeping effect of high-concentration CO2 modified atmosphere packaging on meat regained interest. Extensive experiments have been carried out with different gases such as CO2, N2, O2, H2 and their combinations to observe the inhibitory effect on microorganisms and the effect on meat. Studies have shown that filling 20% CO2 in modified atmosphere packaging can inhibit the growth of Gram-negative bacteria in meat and extend the shelf life. At the same time, adding less than 5% O2 to the modified atmosphere can make the meat in the bag appear bright red color. However, subsequent research also found that although the addition of oxygen made the flesh red and bright at first, the flesh became more brown in the future and the storage period was significantly shortened.
By the 1980s, a large number of experiments and practices proved that 100% pure CO2 modified atmosphere packaging was the most ideal way to keep fresh meat. By studying the effects of various gases and their combinations on the growth of the microorganisms on the meat and the color of the meat, it was found that under the refrigerated condition at 0°C, filling with oxygen-free CO2 to saturation can greatly improve the shelf life of fresh meat and prevent the color of the meat from Oxidative browning due to low oxygen partial pressure. If the microbial contamination can be effectively prevented from slaughter to packaging and storage, fresh meat can reach a storage period of 20 weeks under 0°C modified atmosphere packaging.
Causes of Deterioration of Fresh Meat
Due to the irrational storage method, the quality of fresh meat will decline during storage, and even spoilage. The deterioration of fresh meat during storage is mainly manifested in the increase of the number of microorganisms and the deterioration of color.
- Meat microbial reproduction causes meat spoilage
The number of microorganisms on the surface of normal fresh meat is less than 20 per cm2. Under aerobic conditions, the dominant bacteria are Pseudomonas, and under anaerobic conditions, the dominant bacteria are lactic acid bacteria. Most of the bacteria live on the surface of the meat. The bacteria on the surface of the meat decompose proteins and other nutrients, making the surface of the meat sticky, producing odor, and spoiling in a short time.
2. Color change
The oxidation of myoglobin in meat to brown oxidized myoglobin affects the color performance of meat. An important sign that consumers judge whether meat is fresh or not is the color of the meat. Bright red meat is the most popular color of fresh meat. The color of the meat depends on the chemical state of myoglobin and hemoglobin.
The flesh that had just been slaughtered was purplish red. When exposed to air, myoglobin is easily synthesized under high oxygen partial pressure, making the meat bright red. It is then further oxidized to form oxidized myoglobin, which darkens the meat to brown. At low oxygen partial pressures, such as in vacuum packaging, oxygenated myoglobin is converted to myoglobin. Under anaerobic conditions, the meat can effectively prevent browning and oxidation.
Mechanism of modified atmosphere packaging for fresh meat preservation
Studies have shown that atmospheric environment and temperature are the main factors affecting the preservation period of fresh meat. In the atmospheric environment at normal temperature, bacteria rapidly multiply and cause fresh meat to deteriorate.
Therefore, lowering the storage temperature and creating an “artificial climate environment” can effectively extend the shelf life of fresh meat.
The fresh meat modified atmosphere preservation mechanism is to fill a certain gas in the package to destroy or change the conditions under which microorganisms depend on survival and reproduction and discoloration in order to achieve the purpose of preservation. Gases for modified atmosphere packaging are usually CO2,O2,and N2, or various combinations thereof. Each gas has a different effect on fresh meat preservation.
CO2 is an inhibitor of modified atmosphere packaging, which has a strong inhibitory effect on the reproduction of most aerobic bacteria and molds. CO2 can also prolong the lag phase of bacterial growth and reduce the rate of its logarithmic growth period, but it has no effect on anaerobic and yeast.
Because CO2 is soluble in meat, it lowers the pH value of the meat and can inhibit some microorganisms that are not resistant to acids. However, CO2 has high permeability to plastic packaging films and is easily soluble in meat, causing the packaging box to collapse and affecting the appearance of the product. Therefore, if CO2 is selected as the protective gas, packaging materials with better barrier properties should be selected.
The fresh-keeping effect of O2 on fresh meat has two main aspects: inhibiting the proliferation of anaerobic bacteria during storage of fresh meat; making the meat color bright red in a short period of time, which is easy to be accepted by consumers, but the addition of oxygen makes the storage life of modified atmosphere packaging greatly shorten. Under 0℃, the storage period is only 2 weeks.
N2 is an inert gas, which has no effect on the packaged material and will not be absorbed by food. Nitrogen has a low permeability to plastic packaging materials, so it can be used as a mixed gas buffer or equilibrium gas, and can prevent the packaging box from being collapsed by atmospheric pressure due to the escape of CO2.
Selection of Modified Gas for Fresh Meat packing
The gas for the modified atmosphere fresh-keeping meat must be a mixed gas composed of one, two or three kinds of gases according to a certain proportion according to the fresh-keeping requirements.
1. 100% pure CO2 modified atmosphere packaging
Under refrigerated conditions (0°C), filling with CO2 without O2 to saturation can greatly improve the shelf life of fresh meat, and at the same time prevent oxidative browning caused by low oxygen partial pressure. Keep pork in this way for at least 15 weeks.
If we can effectively prevent microbial contamination from slaughter to packaging and storage, the storage period can reach 20 weeks. Therefore, pure CO2 modified atmosphere packaging is suitable for wholesale, long-distance transportation, and requires a longer shelf life. In order to make the meat color bright red, which is loved by consumers, before retail, change to oxygen-containing packaging, or use polystyrene trays to cover the polyethylene film packaging form, so that oxygen and meat contact to form bright red oxygenated myoglobin Attract consumer purchases. Fresh meat that has been changed to retail packaging can be stored for about 7 days at 0°C.
2. Modified atmosphere packaging of 75% O2 and 25% CO2
Meat packing with a mixed gas consisting of 75% 02 and 25% CO2 can not only form oxygenated myoglobin, but also preserve the meat in a short period of time. It can be stored for 10~14 days under the refrigerated condition of 0℃. This modified atmosphere fresh meat is a retail package suitable for local sale only.
3. 50% O2, 25% CO2 and 25% N2 modified atmosphere packaging
Meat packing with a mixed gas composed of 50% O2, 25% CO2 and 25% N2 as a protective gas, which can not only make the meat color bright red, antiseptic and freshness, but also prevent the packaging box from being collapsed by atmospheric pressure due to CO2 escape . This modified atmosphere packaging is also a form of retail packaging suitable for sale in local supermarkets. Under 0℃ refrigerated conditions, the storage period can reach 14 days.
The preservation effect of pork with different gas formulas is shown in Table 3.6. It can be seen from Table 3.6 that 100% CO2modified atmosphere packaging has the best antiseptic effect and the worst flesh color, but once it is exposed to oxygen again, the flesh color will improve. 75% O2 and 25% CO2 have the best flesh color, but the worst preservative effect and the shortest shelf life.
Matters needing attention in fresh meat modified atmosphere packaging
The freshness preservation effect of modified atmosphere packaging of fresh meat depends on the following 4 factors:
(1) Hygienic indicators of fresh meat before packaging.
(2) Barrier properties and sealing quality of packaging materials.
(3) Proportion of gas used.
(4) Storage temperature of packaged meat.
Therefore, attention should be paid to the following issues in the modified atmosphere packaging process of fresh meat:
- Handling of fresh meat before packaging
After the pigs are slaughtered, if they are cooled at a temperature of 0 to 4°C for 24 hours, the ATP activity in the fresh meat can be suppressed and the acid removal process can be completed at the same time. This acid-cooled meat has better nutrition and taste than quick-frozen meat. In addition, in order to ensure the fresh-keeping effect of modified atmosphere packaging, the hygienic index of fresh meat before packaging must be controlled to prevent microbial contamination.
- Selection of packaging materials
Modified atmosphere packaging should use packaging materials with good barrier properties to prevent the gas inside the package from escaping, and also to prevent the infiltration of O2 in the atmosphere. As the modified atmosphere packaging of fresh meat, it is required to have good barrier properties to CO2 and O2. Generally, a composite packaging film using PET, PP, PA, PVDC, etc. as the substrate is selected.
- Ensure the quality of inflation and sealing
The control of inflating and sealing quality must rely on advanced MAP modified atmosphere packaging machines and good operating quality. For example, thermoforming MAP packaging machines, from container forming, filling, vacuum inflating to sealing, printing date and product output. It is completed automatically and continuously on one machine. It is not only efficient and reliable, but also reduces various pollution during the packaging operation, which is conducive to improving the preservation effect.
- Control of product storage temperature
The effect of temperature on the preservation effect comes from two aspects: one is that the temperature directly affects the activities of various microorganisms on the surface of the body; the other is that the barrier properties of packaging materials are closely related to temperature. The higher the temperature, the less the barrier properties of the packaging material. Therefore, it is necessary to achieve temperature control in the whole process from product, storage, transportation to sales.
Shandong Kangbeite Packaging Machinery Co., Ltd. supplies MAP modified atmosphere packaging machine with world’s cutting-edge technology, ensures the best packaging quality for fresh meat and meat products. Visit the product page for MAP modified atmosphere packaging for details.