Controlled atmosphere technology for fresh keeping

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The application of modified atmosphere packaging technology in the food industry

modified atmosphere packaging is also known as map or cap in foreign countries and in China. 3. it can be divided into low cycle fatigue test, high cycle fatigue test, modified atmosphere packaging or replacement gas packaging and inflatable packaging according to the cycle of stress (strain) cycle when the sample is broken. The commonly used gases are N2, O2, CO2, mixed gas O2 + N2 or Co2 + N2 + O2 (that is, Ma plastic packaging material enterprises can make further improvement and promotion by making reference to the following aspects: P). Modified atmosphere packaging technology can be widely used in the preservation of all kinds of food, extending the shelf life of food and enhancing the value of food

I. application of CO2 in food packaging

a Swedish company introduced the use of packaging bags, containers and storage rooms filled with 100% CO2 gas to store meat. High concentration of CO2 can hinder the propagation of aerobic bacteria, molds and other microorganisms, prolong the stagnant period and exponential growth period of microbial growth, and play an anti-corrosion and anti mildew role. This method can keep pork for 120 days without freezing treatment. If it is pressurized again, the storage time will be longer. This method has aroused great concern of meat exporting countries such as the United States and Australia

recently, American experts adopted new technology to make plastic packaging materials with CO2. That is, using a special catalyst, CO2 and ethylene oxide (or propylene oxide) are mixed in equal quantities to make a new plastic packaging material, which is characterized by glassy transparency and airtightness; Similar to polycarbonate and polyamide resin; It will not completely decompose into gas at 240 ℃; It has the characteristics of biological decomposition and will not pollute the environment and soil

China has successfully researched and used nanotechnology to efficiently catalyze CO2 to synthesize degradable plastics. That is, the catalyst for making plastics from CO2 is "crushed" to the nanometer level to realize the polymerization of catalytic molecules and CO2, so that each gram of catalyst can catalyze about 130 grams of CO2 to synthesize a new packaging material containing 42%co2. As an environmental protection material with excellent degradability, it has a broad application prospect

II. Application of nitrogen in food packaging

nitrogen (N2) is an ideal inert gas. It has unique effects in food packaging: it does not react with food and is not absorbed by food. It can reduce the oxygen content in the packaging, greatly inhibit the growth and reproduction of bacteria, molds and other microorganisms, slow down the oxidative deterioration and decay of food, so as to keep food fresh. Nitrogen filled packaged food can also prevent food from crushing, sticking or shrinking into a ball, and maintain the advantages of food geometry, dryness, crispness, color and flavor. At present, nitrogen filled packaging is rapidly replacing the traditional vacuum packaging, and has been applied to fried potato chips and chips, oil cooked food, etc. Being loved by consumers, especially children and young people, nitrogen filled packaging is expected to be applied to more food packaging

in the United States, N2 is used to increase the strength of thin aluminum beverage cans, and nitrogen is dissolved in the beverage before the beverage is filled; After the beverage can is sealed, the nitrogen is released from the beverage, forming a pressure on the can wall, making the beverage can equivalent to an inflatable can, thereby increasing the strength of the beverage can, and the effect is remarkable. The canned beverage will not be damaged during transportation, stacking or on the shelf, nor will it affect the quality of the beverage. This method can also be used for beverage packaging made of polyester plastics

attention must be paid to the purity and quality of N2 in N2 application. The purity of nitrogen separated from compressed air by membrane separation or pressure swing adsorption can reach more than 99.9%. The purity of N2 used in food packaging must reach the pure nitrogen level (i.e. safety level)

III. application of composite gas in packaged food

composite modified atmosphere fresh-keeping packaging is collectively referred to as map packaging in the world. The modified atmosphere fresh-keeping gas used is generally composed of CO2, N2, O2 and a small amount of special gas. CO2 can inhibit the growth and reproduction of most aerobic spoilage bacteria and molds; O2 inhibits the growth and reproduction of most anaerobic spoilage bacteria; Maintain fresh meat color, oxygen rich respiration and freshness of fresh fruits and vegetables; N2 is used as filling gas. The composition ratio of compound gas shall be properly selected according to the type of food, preservation requirements and packaging materials, so as to achieve the effect of high fresh-keeping quality of packaged food, good nutrient composition, real original properties and delay the shelf life of fresh-keeping

composite modified atmosphere fresh-keeping packaging has been widely used at home and abroad

▲ modified atmosphere packaging of fresh fish and shrimp the deterioration of fresh aquatic and marine fish mainly includes the decomposition of trimethylamine oxide in fish flesh by bacteria to release trimethylamine with putrid taste, oxidative rancidity of fish fat, softening of fish flesh by enzyme degradation in fish body, and toxic toxins produced by bacteria (aerobic Escherichia coli and anaerobic clostridium) on fish surface, which endanger human health

the gas used for modified atmosphere packaging of fish is composed of CO2, O2 and N2. The concentration of CO2 is higher than 50%, which can inhibit the growth of aerobic bacteria and mold without making fish exude; O2 concentration of 10% - 15% inhibited the propagation of anaerobic bacteria. The gills and viscera of fish contain a large number of bacteria, which should be removed, cleaned and treated with disinfectant before packaging. As CO2 is easy to seep out of plastic film, the packaging material for modified atmosphere packaging of fish needs composite plastic film with high gas barrier, which can be maintained for 15-30 days at 0 ℃ - 4 ℃. British tuna is packaged with 35% - 45% CO2/55% - 65%n2 gas for preservation, with a shelf life of 6 days

the deterioration of shrimp is mainly caused by microorganisms. Its intrinsic enzyme action causes the shrimp to blacken. The modified atmosphere packaging can keep the shrimp fresh. The shrimp was first soaked in 100mg/L lysozyme and 1.25% sodium bisulfite fresh-keeping solution, and then 40% CO2 and 60% N2 mixed gas were used to fill the inflatable adjustable packaging bag. The shelf life of the shrimp was 22 days longer than that of the control sample, which was 6.5 times that of the control sample

▲ modified atmosphere packaging for fresh meat of poultry and livestock

the modified atmosphere packaging for fresh pork, sheep and cattle should not only keep the original red color of fresh meat, but also preserve its freshness. The gas in the modified atmosphere packaging is composed of O2 and CO2. The gas composition varies according to the type of meat. The gas composition of modified atmosphere packaging of pork is 60% - 70%o2 and 30% - 40% CO2. The shelf life at 0 ℃ - 4 ℃ is generally 7-10 days (including the chilled pork that is cooled at 0 ℃ - 4 ℃ for 24h after slaughter to lose ATP active substances and become soft, fragrant and palatable). Modified atmosphere packaging of poultry meat is mainly used for preservation. The gas used for preservation is composed of CO2 and N2. Poultry meat is packaged with 50% - 70%co2/50% - 30%o2 at 0 ℃ - 4 ℃ for 14 days

in the modified atmosphere fresh-keeping packaging of meat, the use of high concentration O2 can make the fresh meat keep bright red and more bright. In the anoxic environment, the meat is light purple. For example, with CO2, N2 and other fresh-keeping gases, the meat color is light purple, and the fresh-keeping period can reach about 30 days. Fresh meat packaging materials also require the use of composite plastic packaging materials with high barrier to gas

▲ modified atmosphere fresh-keeping packaging for baked goods and cooked food products

baked goods include cakes, cakes, biscuits, bread, etc., and the main component is starch. Spoilage caused by bacteria and mold, rancidity and deterioration caused by fat oxidation, aging and hardening of starch molecular structure, etc. cause food deterioration. The gas used in the modified atmosphere packaging of this kind of food is composed of CO2 and N2. Cakes without cream can be kept fresh for 20-30 days at room temperature. Moon cakes and pudding cakes can be kept fresh for 60-90 days at room temperature with high barrier composite film

microwave dish software can customize dishes, bean products and cooked meat products of livestock and poultry. Filling CO2 and N2 can effectively inhibit the propagation of coliform bacteria. It shall be kept fresh for 5-12 days at room temperature of 20 ℃ - 25 ℃, kept fresh for about 30 days at room temperature after conditioning and sterilization at 85 ℃ - 90 ℃, and kept fresh for 60-90 days at 0 ℃ - 4 ℃

▲ modified atmosphere fresh-keeping packaging of fresh fruits and vegetables can still maintain the metabolism of absorbing oxygen and discharging CO2 after harvest, and consume nutrition at the same time. Fresh keeping of fruits and vegetables is to reduce the content of O2 in the environment and low-temperature storage, reduce the respiratory progress, eliminate the CO2 produced by respiration, and delay the ripening and senescence of fruits and vegetables, so as to achieve the fresh-keeping effect. The modified atmosphere packaging gas for fruits and vegetables is composed of O2, CO2 and N2. The fruits and vegetables are packed with breathable film, filled with low O2 and high CO2 and sealed after replacement with mixed gas, so that the O2 content in the package is lower than the air and the accumulated CO2 is higher than the air. The gas exchange is carried out through the film, so as to achieve the controlled atmosphere balance that is conducive to the fresh environment of fruits and vegetables and maintain weak aerobic respiration

most fruits and vegetables are packed in a mixed proportion of 5%o2, 5%co2 and 90%n2, and have a long preservation period at 6 ℃ - 8 ℃. Modified atmosphere packaging is used for litchi preservation and preservation. The litchi fruit treated with 10%co2 + 90%n2 and 20%co2 + 80%n2 for 24hr can not only achieve the purpose of preservation, but also improve the good fruit rate of the fruit, keep the peel red, and do not affect the nutritional components. The strawberry shelf life can be prolonged by 8-10 days under high CO2 and low oxygen conditions combined with ozone treatment (4.3mg/m3 concentration) and thin edible coating

American scientists used modified atmosphere packaging test on mango. Mango was peeled and cut into pieces. Oxygen packaging, mixed gas (n286%, co210%, o24%) packaging and vacuum packaging were used respectively. The results showed that mango packaged with mixed gas had the longest shelf life. During storage, mango had good color, texture and other appearance effects, and the damage caused by microorganisms was the least

modified atmosphere packaging is also suitable for fresh keeping of clean vegetables. Clean vegetables are also called cut fruits and vegetables and semi processed fruits and vegetables. In order to cater to the emerging food processing products of office workers, they are safe, fresh, nutritious and convenient, but they are easy to browning after cutting. Using modified atmosphere packaging to reduce oxygen content can maximize shelf life. For example, cut lettuce in the United States can prevent browning with 1% - 3% O2, 5% - 6% CO2 and 90%n2. The modified atmosphere fresh-keeping package is also suitable for the fresh-keeping of peeled and sliced apples, potatoes, leafy vegetables and other fruits and vegetables. It is the key to broaden the fresh-keeping ways of fruits and vegetables to develop the packaging film suitable for the fresh-keeping effect of modified atmosphere packaging of fruits and vegetables

reprinted from: Food talk and food talk

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