With the continuous improvement of living standards, people have higher and higher requirements for food, not only fresh and high quality, but also nutritional safety. However, food is prone to spoilage during storage and transportation, which reduces the quality and nutritional value of the food, and even produces harmful substances when it is serious, endangering human health. Food spoilage is the result of food oxidation or the reproduction of microorganisms and insects such as mold, bacteria, yeast. Food oxidation is caused by the direct action of oxygen, and the growth of microorganisms and insects is also closely related to oxygen. Therefore, it is very important to remove oxygen from food. Deoxygenation packaging technology is to use the removal of oxygen in food packaging to achieve food preservation and quality. At present, deoxidizing packaging technology has been widely used in the food industry.
First, the definition and characteristics of deoxygenation packaging technology
1. Definition of deoxygenation packaging technology Deoxygenation packaging refers to sealing in a sealed packaging container with a deoxidizing agent capable of chemically interacting with oxygen, thereby removing the oxygen in the packaging, so that the oxygen content of the packaged material is very low, or even almost oxygen-free. A packaging technology that is preserved under conditions.
2. Characteristics of deoxygenated packaging technology Deoxygenated packaging is a new packaging method formed after the emergence of vacuum and inflatable packaging. Compared with vacuum and inflatable packaging technology, the most significant feature is that it can reduce oxygen in sealed packaging. At very low levels, it even creates an almost oxygen-free environment. This is because the deoxidizer can not only remove all the oxygen in the packaging container, but also remove the oxygen that has penetrated into the packaging from the external environment and the oxygen that is dissolved in the liquid or filled in the pores of the solid sponge-like structure.
In addition, deoxidation packaging technology has the following characteristics compared with other packaging technologies: food additives can be reduced or not added in the food production process, so that food additives are more secure; food oxidation can be prevented Damage, such as preventing odor from fats and fats, avoiding discoloration of animal and plant tissues (such as meat) and loss of flavor, and reducing loss of nutrients, so as to better maintain the original color, aroma, taste and nutrition of the product; can Effectively prevent or delay the deterioration caused by aerobic microorganisms, so as to extend the shelf life appropriately. In summary, deoxygenation packaging technology is an efficient, convenient and safe food packaging technology.
Classification of deoxidizers and their mechanism of action 1. Classification of deoxidizers can be divided into two categories according to their components. One is an inorganic deoxidizer, that is, a deoxidizer based on an inorganic matrix, such as an iron deoxidizer, Sulfite-based deoxidizers, hydrogenation catalyst-type deoxidizers, etc .; the other is organic-based deoxidizers, which are deoxidants based on organic substrates, such as enzymes, ascorbic acids, oleic acid, linoleic acid, or tocopherols. Wait. Among them, iron-based deoxidizers with widely available raw materials, low cost, good deoxidizing effect, and high safety are the most widely used.
According to the classification of reaction types, they can be divided into self-reactive type (that is, the deoxidizer contains water in advance, and it starts to absorb oxygen immediately upon contact with oxygen) and water-dependent type (that is, the one that starts to absorb oxygen after absorbing water from food) Moisture) two broad categories. Self-reactive deoxidizer is mainly used for foods with low water activity such as tea, nori, laver, nuts and dry materials. Moisture-dependent deoxidizers are suitable for foods with high water activity such as rice cakes, bean paste, and pizza crusts.
2. Mechanism of common deoxidizers
The deoxidizer uses the principle that it has a reducing effect and can react with oxygen to remove the oxygen in the package. The mechanism of the deoxidation reaction varies with the deoxidizer. The following briefly introduces the deoxidation mechanism of several commonly used deoxidants.
(1) Iron-based deoxidizer This is a widely used type of deoxidizer. The deoxidation method using iron powder as the main agent and the iron powder series deoxidizer mainly uses the principle of iron oxidation and rusting. The main reactions in the deoxidation process are as follows:
Reactions (1) and (3) can remove oxygen from the package, and reaction (2) is one of the possible side reactions. The net product of this reaction, 4Fe (OH) 3, is commonly known as rust. The actual rust is composed of α-FeO (OH) and β-FeO (OH) hydrate, so the chemical formula should be expressed as Fe2O3 · 3H2O. From the reaction mechanism point of view, iron-based deoxidizer should have water in the reaction, so it is suitable for deoxidation of food with higher water content.
Under standard conditions, according to theoretical calculations, 1g of iron powder can react with 300mL of oxygen. The LD50 of iron is 16g / kg. The dosage of the bagged deoxidizer in commercial use is up to 7g of iron powder, so for a person weighing 70Kg, the relative dose is only 0.1g / kg. Therefore, iron-based deoxidizers are safe and efficient, but also have disadvantages, such as being unable to pass through metal detectors installed on packaging production lines.
(2) Sulfate-based deoxidizer This deoxidizer is mainly based on dithionite, with calcium hydroxide and activated carbon as auxiliary agents. If an appropriate amount of sodium bicarbonate is added to the auxiliary, in addition to removing the oxygen in the packaging space, carbon dioxide can be generated to form a high carbon dioxide environment in the packaging, which can further improve the protection effect of the product. The reaction mechanism is as follows:
Reaction (4) is the main deoxygenation reaction, and Ca (OH) 2 is mainly used to absorb SO2. Activated carbon and water are the catalysts for reaction (4), so the amount of activated carbon and the relative humidity of the packaging space will affect the deoxidation rate to varying degrees. According to theoretical calculations, 1g of sodium dithionite can remove 130ml of oxygen. Its deoxidation capacity is not as good as iron-based deoxidants, but it has a fast deoxidation speed and can generate carbon dioxide, which is very beneficial for food storage and freshness preservation.
(3) Hydrogenation catalyst-type deoxidizer The earliest deoxidizers based on hydrogenation catalysts such as platinum, rhodium, and palladium were used. Among them, palladium is more commonly used. In the activated state, the hydrogenation catalyst with micropores can adsorb active hydrogen that is many times larger than its volume, and can catalyze the reaction of hydrogen and oxygen to generate water, so that the purpose of removing oxygen in the package can be achieved. If a water-absorbing agent or desiccant is added to the package, the water generated by the reaction can be removed. This kind of deoxidizer is high in cost, inconvenient to use, and the scope of use is also limited to a certain extent. Therefore, it is only used in special occasions or in combination with other deoxidants in small amounts.
(4) Glucose oxidase This method uses enzyme technology. Glucose oxidase usually uses immobilization technology and packaging materials . Under certain temperature and humidity conditions, it uses oxygen to oxidize glucose to gluconic acid to achieve deoxygenation. The suitable conditions for this reaction are 30-50 ° C, pH 4.8-6.2. The glucose in the reaction can come from the food itself, or it can be added later. This type of deoxidizer is currently only used in the packaging of certain products.
(5) Ascorbic acid deoxidizer Ascorbic acid (AA) itself is a strong reducing agent. In the presence of oxygen, it can be oxidized to form oxidized ascorbic acid (DHAA) to remove oxygen in the environment. This method is commonly used to remove Oxygen, the reaction is as follows:
AA + 1 / 2O2 → DHAA + H2O (7)
Ascorbic acid is vitamin C, so the use of ascorbic acid deoxidizer is safer. The oxidation amount of ascorbic acid in this system can be used to determine the oxygen content in liquid food.
III. Development of deoxygenated packaging technology The bagged deoxidants used in deoxygenated packaging have the problem that they may be ingested by consumers, and may leak and contaminate food. To eliminate these problems, deoxidizers can be synthesized into packaging materials, such as deoxidizer flakes, polymer films , labels, bottle caps or gaskets.
1. The deoxidizer sheet has a patent proposed to make the deoxidizer into a laminated sheet, which can prevent consumers from eating it by unpacking the deoxidizer packet. The preparation method is: 100g of iron powder and 1g of activated carbon and 20% of 5g The sodium chloride solution was thoroughly mixed. After evaporation and drying, 100g of it was mixed with 10g of pulp and 20g of PE fiber, and then evenly coated on non-woven fabric, and then heat-melted (180 ° C, 0.2) kg / cm2) into a sandwich laminated sheet.
2. Deoxidizing film In 1970, Kuhn proposed that a palladium sheet or platinum sheet be embedded between a barrier layer and a breathable layer to make a laminated deoxidizing film. It uses the principle of palladium or platinum sheet to catalyze the action of oxygen and hydrogen in the packaging to produce water, and achieves the effect of deoxidation. Later, American Can changed the two-layer ionic membrane to embed the palladium tablets. It was found that the product has better deoxidation efficiency, which can reduce the oxygen concentration in the package to less than 0.001%, and it can be maintained for 6 months, but The use of this type of deoxidizing film must first replace the gas in the package with 92% nitrogen and 8% hydrogen, and the palladium and platinum tablets are quite expensive, so the use is not common. The deoxidizing membrane products studied in recent years can be roughly divided into the following three categories.
(1) Photochemical deoxidation film In 1981, the CSIRO Institute in Australia developed a special photochemical deoxidation film. The principle is to apply a photochemical dye and an active oxygen acceptor to an ethyl fiber film. When light is irradiated to the dye, it is The excited dye will transfer energy to the oxygen in the package to form excited active oxygen, which is then received by the active oxygen acceptor to achieve the effect of deoxygenation. This kind of photochemical deoxidation film is mainly used on bottle caps. The quality stability of rapeseed oil has been tested in packaging tests. The results show that the use of deoxidation film packaging can reduce the peroxide value by about 66%. However, in the environment of insufficient light, it cannot work, which is its biggest disadvantage.
(2) Embedding deoxidizing film Mitsubishi Gas Chemical Co., Ltd. has launched a new thin-film deoxidizer product called "Agilance Omak". At present, it has been widely used in high-value, high-temperature and high-pressure sterilized food flexible packages that need to maintain excellent food flavor without additives. The deoxidized absorption of "Agilance Omak" is 0.1 to 0.5 ml / cm, the suitable water activity that must be provided at the beginning of the deoxygenation reaction is 0.85 or more, and the thickness of the film is 100 to 300 μ. The film used in this product consists of a four-layer structure including an outer layer, a barrier layer, an oxygen absorption layer and an inner layer. The oxygen absorbing layer is a polyolefin film with an iron-based oxygen absorber; the barrier layer is composed of a thin film of aluminum foil, MXD6, EVOH, and a thin layer of evaporated silica. After food packaging, it can play a role in preventing external oxygen from attacking; The layer is also a polyolefin film; the outer and inner layers are made of plastic film materials such as PET and nylon.
(3) Deoxygenation membranes of immobilized enzymes. There are many studies in Japan that integrate enzyme systems (glucose oxidase, catalase) with immobilization technology in chitosan, polypropylene (PP), or polyethylene (PE), etc. On the film, the principle of catalyzing the oxidation of glucose to gluconic acid by enzymes is used as a deoxygenation system in liquid food packaging. The glucose required for the enzymatic reaction can be embedded in a packaging film using microcapsules or directly provided by food. Under ideal conditions, 0.78g of glucose can completely remove oxygen in 500ml of air after oxidation. However, its biggest disadvantages are that the enzyme is easily inactivated during the preparation process, and the deoxygenation effect is not easy to control, so there are not many commercial products.
Application of deoxygenation packaging technology in the food industry
The application of deoxygenation packaging technology in the food industry is not long. It first appeared in 1925, but it was not used in conjunction with materials with high sealing and barrier properties until the late 1970s, and was applied to food packaging. At present, the application of deoxidizers in different food processing is: 45% of pastry sweets, 30% of processed foods of livestock, aquatic products and agricultural products, 15% of tea, coffee, etc., 10 of other foods such as healthy food, home-made dishes %, Has been widely used in foods with high moisture content, foods with short shelf life, and medicines and health foods with long shelf life.
1. Application in pastry food Pastry is one of the earliest and most widely used deoxidizing packaging technology to achieve preservation and preservation of food. Most of the pastry foods contain high oil and fat, and the structure is soft or crunchy. It is not suitable to use vacuum packaging, otherwise it is easy to deform, especially moon cakes and biscuits. It has a long storage period and is prone to oxidative corruption. Bread and cakes are likely to cause mold growth. If a deoxidizer is sealed in the package, not only the oxygen is removed, but the most important thing is to prevent the fat from oxidizing and causing the product to have a bad taste or mold growth, thereby extending the shelf life. In addition, since the deoxidizer has a good inhibitory effect on the growth of aerobic microorganisms, it has a significant effect on the preservation of foods such as cakes and rice cakes. At present, China's deoxidation packaging technology is most widely used in the packaging of moon cakes. The deoxidizers in moon cake boxes are mainly iron-based deoxidants.
2. Application in meat food processing and storage It is used to prevent myoglobin from being oxidized during the storage of fresh meat to achieve the function of deoxidation and color protection. This is because fresh meat is prone to change in color during storage. Under the action of oxygen in the air, the purplish myoglobin can be oxidized to bright red oxygenated myoglobin and produce the familiar "redness" of meat. "sense. Using this principle, the use of deoxygenated packaging can make the packaging environment reach a substantially anaerobic state for a short time. At this time, myoglobin is not oxidized and is in a purplish red state. Once the package is opened, the meat is immediately oxidized to oxymyoglobin With "fresh meat" color, so as to achieve the role of oxygen and color protection. In addition, it has the effects of preventing fat oxidation, preventing mold proliferation, and maintaining flavor for cooked meat products. Currently, deoxidizing packaging technology is widely used in ham and sausage.
3, the application in tea packaging The role in tea packaging is mainly to prevent brown discoloration, to prevent vitamin oxidation. The chlorophyll, catechins, lipids, chlorophyll and Vc in tea are very easy to be oxidized, especially the changes of green tea are particularly prominent. Once oxidized, it will lose the tender green color and yellow, which has a great impact on quality. Therefore, if moisture-proof and light-shielding are added together with deoxygenated packaging, the green tea can still maintain the fresh state of the soup and clear leaves after being stored at low temperature for one year.
4. Application in coffee packaging In order to maintain the proper flavor of pure coffee products, some manufacturers also use deoxidizing packaging technology when producing simple enjoyable small-package coffee products. This is to prevent the oxidation reaction from destroying the pure aroma of coffee. A large amount of CO2 is generated when the coffee beans are roasted, and the packaging is immediately sealed after roasting. The CO2 will swell or even rupture the bag. Therefore, by adding a CO2 absorbing deoxidizer in the packaging bag , it can absorb 10 times the volume of CO2 of oxygen for a long time, and achieve the effects of preventing oxidation and keeping fragrance.
5. Application in grain storage Adults and eggs in cereal legumes have serious harm to food quality. Deoxygenation packaging technology can make the insects suffocate by hypoxia, prevent mold breeding, and prevent insects such as rice and peanuts. The phenomenon of moth and mildew makes rice, wheat, mung bean, soybean and other foods preserve for a longer time.
6. Application in aquatic product packaging Deoxygenated packaging technology is applied to aquatic products, which can prevent the breeding of worms and molds. In addition, the application of aerobic packaging technology to aquatic products can make seafood, fish, crabs, shrimps and other seafood stored in packaging bright in color. At present, deoxidizing packaging technology is widely used in refined aquatic products, especially dried fish and fillet products.
7, other foods Deoxy packaging technology can be applied to the packaging of many foods. For example, puffed foods are a large class of foods with frying as the main process, and the fat is easily oxidized. The oxygen in the sponge structure after puffing can be removed through deoxidation packaging to achieve the effect of extending the storage period. In peanuts, walnuts, sesame and other nuts with high fat content, the effect of preventing fat failure is also very prominent. It can also be used in milk powder and soybean powder to prevent the oxidation of fat, and can reduce the adverse effect of powder cakes on the conditioning performance after using air-packing. Protects against vitamin degeneration and discoloration in dried products or powders of fruits and vegetables. It is also widely used in medicine and cosmetics.
V. Prospect At present, the good deoxidation effect of deoxidizers has made deoxidation packaging as a new type of packaging method flourish in China and around the world. Various new types of deoxidizers have been developed and used for a wider range of purposes. With the development of science and technology, new and efficient deoxidizers will continue to meet market demand, and it will also bring an innovation to China's packaging industry and related supporting industries.