Fresh Food | Modified Atmosphere Packaging (MAP) Technology
Fresh fish, poultry, meat, fruits and vegetables are the most consumed food in urban and rural areas in China. One of the most concerned topic among agriculture, food enterprises and supermarkets is how to protect fresh food. At present, in supermarkets, fresh food is only sold by dividing and weighing raw materials into plastic shallow plates and wrapping them with plastic film and then placing them in low temperature refrigerator. The shelf life is usually 2 to 3 days. However from production and sales to consumers, it at least needs 6-7 days with refrigerated fresh-keeping, 2-3days can’t meet the requirement. This restricts the production and development of fresh food. In addition, unwashed and processed primary packaging fresh food are not convenient, which spends a lot of time and labor to deal with, obviously can not meet the city kitchen project for consumers to provide ready-to-eat cooking condition. Slaughtered and processed live poultry is sold with packaged, which can not only keep fresh, but also avoid human infection of avian influenza virus and maintain urban sanitation. Tuna is a delicious and nutritious fish. Due to the lack of deep-frozen cold chain preservation, it can not be preserved after being caught in the ocean and shipped back to the domestic market. If it can keep fresh packaging, it can enrich the market supply.
Modified atmosphere fresh-keeping packaging (MAP) technology is a new packaging technology that extends the shelf life of fresh food and has been widely used abroad. For example, British tuna adopts 35% ～ 45% CO2 and 55% ～ 65% N2 modified atmosphere fresh-keeping packaging for 6 days, while poultry adopts 25% ～ 35% CO2 and 65% ～ 75% N2 modified atmosphere fresh-keeping packaging for 6 days. 7 days. The modified atmosphere packaging technology of fresh food requires that the raw materials be fully cleaned and cleaned, and then divided and weighed. The consumer can adjust the cooking after purchasing. This packaging meets the packaging requirements of kitchen engineering. Therefore, the application of modified atmosphere fresh-keeping packaging technology can solve the problem of fresh food preservation. Modified atmosphere fresh-keeping packaging The protective gas composition and packaging materials need to be determined according to the anti-corrosion and fresh-keeping mechanism of various fresh foods to obtain an effective and longest shelf life. The author has done long-term research on modified atmosphere fresh-keeping packaging of fresh food, and experiments have proved that this kind of fresh-keeping packaging technology is effective.
Fresh-Fish Modified Atmosphere Packaging Fresh fish is a food that is prone to spoilage and difficult to preserve. The main factor of spoilage is the growth and reproduction of spoilage bacteria. Currently, ice is added to cool and keep fresh, but the surface of the fish will be seriously polluted after melting. The total number of bacteria contaminated on the surface of fish is as high as 106-108, but it accelerates corruption and shortens the preservation period. The bacteria contaminated by fish in water are aerobic E. coli and anaerobic clostridia. The latter produces toxins that cause food poisoning when the temperature is higher than 4 ℃. The danger of this toxin is that it occurs in fish. Before somatosensory corruption. The principle of modified atmosphere packaging of fish is to use protective gas to inhibit the growth of spoilage bacteria. The composition of protective gas is composed of CO2, O2 and N2. composition. CO2 has a strong inhibitory effect on most aerobic bacteria and molds, but it cannot inhibit anaerobic bacteria. Its effective bacteriostatic concentration is about 25%. The CO2 in the package is easily soluble in the moisture and fat of the fish meat and reduces the bacteriostatic concentration.
Therefore, the CO2 concentration in the protective gas is higher than 50%, and the excessively high CO2 concentration will cause the fish meat to leak out the fish juice and the freshness changes. The concentration of O2 in the protective gas is about 10% to 15% to inhibit the growth of anaerobic bacteria. The structure of various fish and meat is different, and the composition and mixing ratio of protective gas can be obtained through experiments. The shelf-life of modified atmosphere fish packaging at 0 ℃ ～ 4 ℃ is usually 7-10 days. The gills and giblets of fish contain a lot of bacteria. Before packaging, they need to be cleaned, cleaned, and disinfected to minimize bacterial contamination. Modified atmosphere packaging can achieve effective preservation and long shelf life. Because CO2 easily oozes out of plastic films, the packaging materials of modified atmosphere packaging for fish need to use PA / PE, PET / PE and other composite plastic films with gas barrier properties.
Modified atmosphere fresh-keeping packaging of fresh meat Modified atmosphere packaging of fresh meat can be divided into two categories: one is pig, beef, and mutton. The meat is red, also known as red meat packaging. It is required to maintain the red color of the fresh meat and be antiseptic. Keep fresh; another kind of poultry meat such as chicken and duck, which can be called white meat packaging, only requires preservation and preservation. Red meat contains bright red oxygenated myoglobin, which can keep the meat color bright red under high oxygen environment, and reduce to light purple myoglobin under hypoxic environment. Vacuum-packed red meat, because the hypoxic meat is lavender, will be mistaken for freshness by consumers and affect sales. The protective gas of red meat modified atmosphere packaging is composed of O2 and CO2. The concentration of O2 needs to exceed 60% to maintain the red color of the meat. The minimum concentration of CO2 is not less than 25% to effectively inhibit the reproduction of bacteria. All kinds of red meat have different myoglobin content, and the redness of the meat is different. For example, beef is darker than pork, so the oxygen concentration of different red meats in modified atmosphere packaging needs to be adjusted to obtain the best color retention and antiseptic effect. . The composition of protective atmosphere of pork modified atmosphere packaging is usually 60% to 70% O2 and 30% to 40% CO2, and the shelf life of 0 ° C to 4 ° C is usually 7 to 10 days. The purpose of modified atmosphere packaging of poultry meat is anti-corrosion. The protective gas is composed of CO2 and N2. Poultry meat is modified atmosphere packaged with 50% ～ 70% CO2 and 50% ～ 30%. day.
Carcasses after slaughter of livestock and poultry are contaminated with a large number of bacteria, and need to be cleaned, cooled, disinfected, treated, divided and weighed, and then modified atmosphere packaging can achieve effective preservation. The packaging material of modified atmosphere packaging for meat is the same as that of fish, and it also requires composite plastic packaging materials with gas barrier properties.
Fresh fruits and vegetables are fresh-keeping after harvest. Fresh fruits and vegetables are still alive, maintaining the metabolic aerobic respiration activity that absorbs oxygen and discharges carbon dioxide, while consuming their nutrients until aging and withering, and fermentation and decay when hypoxia is also called anaerobic respiration. Reducing storage temperature and reducing the oxygen content of the environment can inhibit the respiration rate of fruit and vegetable metabolism, thereby delaying the aging of fruits and vegetables and keeping them fresh. Tests have shown that most fruits and vegetables to reduce oxygen content and increase carbon dioxide content (compared to air) is better than reducing oxygen and keeping fresh, but too low O2 such as 2% will cause anaerobic respiration of fruits and vegetables, and too high CO2 such as 15% of fruits and vegetables will have physical damage such as black spots. The fresh-keeping principle of modified atmosphere packaging for fruits and vegetables: Packing fruits and vegetables with a breathable film, filling the mixed gas of low O2 and high CO2 to replace the air, and sealing. The accumulation of CO2 is higher than that of air, and the gas exchange is carried out through the membrane to achieve an air-conditioning balance that is conducive to the maintenance of weak aerobic respiration of fruits and vegetables and is kept fresh. The condition of the modified atmosphere of the modified atmosphere packaging of fruits and vegetables is that the respiration rate of the fruits and vegetables in the packaging should match the permeability of the plastic film. Therefore, the fresh-keeping effect of modified atmosphere packaging of fruits and vegetables depends largely on the packaging materials. At present, the modified atmosphere packaging materials used for low respiration rate fruits and vegetables (such as tomatoes, etc.) have 0.03 ～ 0.04mm PE, PP and PVC films, but they cannot meet the packaging requirements of high respiration rate tropical fruits or leafy vegetables. At home and abroad, various microporous films with high air permeability are being researched and developed to meet the requirements of modified atmosphere packaging for various fruits and vegetables.
Although there are many varieties of fruits and vegetables, the respiration rate of various fruits and vegetables is quite different, and the mixing ratio of the lowest O2 and the highest CO2 in the modified atmosphere packaging is difficult to determine, but most fruits and vegetables use 5% O2, 5% CO2 and 90% N2 gas mixed ratio packaging can obtain a freshness period of 1 to 2 times larger than that of air packaging at a low temperature of 6 ℃ to 8 ℃. Such fresh-keeping period still has certain market benefits for supermarket sales and short-distance transportation.