New Progress in Fresh-keeping Packing for Vegetables and Fruits

With the development of economy and the improvement of living standards, people's dietary life has transitioned from the past single-subsistence mode to the current diversified nutrition type. At present, the demand for vegetables and fruits is increasing, and the demand for freshness is also increasing.
Fruits and vegetables are stored during the maintenance of life through the respiration. During the breathing process, fruits and vegetables absorb oxygen, exhale carbon dioxide, produce ethylene gas, and reduce moisture. Respiration results in the depletion of internal components, flesh softening, and reduced nutritional value; ethylene gas can promote the aging of fruits and vegetables and accelerate the respiration; the moisture content of fruits and vegetables is as high as 85% to 95%, if the loss of water reaches 5%, The appearance will be wilting and reduce the value of the commodity; if it turns yellow, the content of vitamin C will be reduced, which shows that the respiration is the main factor affecting the freshness of vegetables and fruits. In addition, the corrosive effect of pathogenic microorganisms is another factor that causes a decrease in the freshness of vegetables.
The so-called food preservation technology is to maintain the freshness of foods and suppress the deterioration of foods. The preservation of fruits and vegetables is mainly to inhibit their respiration and proliferation of bacteria. The respiration of fruits and vegetables and the increment of microorganisms are related to the storage temperature, humidity and gas composition. In general, low temperature, high humidity, low oxygen, high carbon dioxide, low ethylene, sterile environment is conducive to the preservation of fresh fruits and vegetables, so the main method of preservation is to maintain low temperature, control the evaporation of water, adjust the gas environment, remove ethylene gas, Sterilization and antibacterial etc. The main materials for keeping fruits and vegetables fresh are functional plastic wrap, new corrugated boxes, and functional preservatives.
Although the traditional film of functional cling film can play the role of packaging and has certain preservation effect, it has obviously failed to meet the preservation requirements of the modern market. Therefore, a large number of new cling film has been developed. These functional cling films not only have the effect of preventing moisture from evaporating in the conventional film, but also have a simple effect of controlling the gas, and further increase the freshness of fruits and vegetables.
Ethylene adsorption film. Ethylene adsorption film is used to remove harmful ethylene gas. Plastic film (especially LDPE) is mixed with gas-absorbing porous material, such as talc and zeolite, quartz stone and silica, clay mineral, stone powder and other micro powders, most of which can be adsorbed. Ethylene or block far-infrared radiation. The mechanism of ethylene adsorption is that the pores on the surface of the porous inorganic material can capture ethylene, and even in the case of high moisture, the water molecules present in the pore can be replaced with ethylene. However, the amount of gas adsorbent added is 3% to 5% because the adsorption capacity of ethylene gas is limited. At present, in the foreign countries, the use of titanite-based films is mainly due to the addition of silicic anhydride-based ceramics.
Anti-dew film. The cling film used for fruits and vegetables is generally a film made of low-density polyethylene, polypropylene, polystyrene, ethylene-vinyl acetate copolymer, and polyvinyl chloride, etc., which are highly gas-permeable, but are packaged using these films. When the water vapor generated from vegetables and fruits is condensed on the inner surface of the film, not only the transparency thereof is poor, but also the water droplets gather, which causes the bacteria to multiply quickly and causes the corruption of vegetables and fruits. The solution to this problem is the prevention of dew film. The anti-corrosion film uses an interfacial agent to treat the inner surfaces of the above-mentioned materials, such as polyethylene, polypropylene, and polystyrene, to absorb excess moisture, and to appropriately maintain the humidity inside the package. The purpose of preservation. The substance that can be used both as a food additive and as a demulsifier is a fatty acid ester.
Antibacterial film. In the antibacterial film, antibacterial silver zeolite is mixed into the film, and silver zeolite is a mixture of silver ions having an antibacterial effect and sodium ions in the crystal structure of zeolite, or a mixture of silver ions and synthetic loose zeolite using aluminum and silicon as raw materials. The main use of PE, PP and PS as a substrate. This film can inhibit the proliferation of bacteria to some extent, play a role in preservation.
Fresh-keeping corrugated cartons Corrugated cartons are currently used as containers for transportation of goods between consumption and production. They have attracted great attention in the preservation of fresh fruits and vegetables.
Corrugated cardboard boxes with thermal insulation. At low temperatures, not only the respiration of vegetables and fruits is weakened, but also the activity of bacteria is greatly reduced. Therefore, low-temperature storage is the most effective means and is the development direction of maintaining the freshness of food.
Corrugated cardboard boxes with thermal insulation have a good fresh-keeping function. This type of corrugated carton is made by laminating a composite resin and an aluminum evaporated film in a conventional carton, an outer package, or adding a foamed resin to a paper core. This type of corrugated box has excellent heat insulation and can prevent the temperature of the fruits and vegetables themselves from increasing during the circulation.
Corrugated box with control of gas function. As described above, adjusting the stored gas components, humidity, and other conditions will also achieve a certain freshness preservation effect, which is an important aspect of the freshness preservation technology.
Corrugated box with control of gas function. The corrugated box with the function of controlling the gas is a porous powder that can adsorb ethylene gas in the inner lining of the carton and the outer lining, or in the papermaking stage. This corrugated box has gas barrier properties to prevent the evaporation of moisture from fruits and vegetables and achieve the effect of controlling the content of gas, thereby maintaining the freshness of fruits and vegetables.
Fresh-keeping sheets, preservatives and cold storage agents In order to enhance the preservation of fruits and vegetables, the aforementioned packaging materials may be used together with substances having specific functions, such as fresh-keeping sheets, preservatives and cooling agents.
Fresh food sheet. The single packaging of fruits and vegetables uses plastic platters and thin film composite products, so the functional sheet placed on the platter body or above has a freshness-keeping function. These sheets often have one or more functions such as humidity control, dew proofing, ethylene gas absorption, and antibacterial. Among them, moisture-adsorption and water-absorption is a multi-layer structure composed of a superabsorbent resin and a non-woven fabric, a thin paper, and a water-absorbing polymer; the absorption of ethylene gas mostly utilizes the porosity of activated carbon; the antibacterial property is due to the addition of a sheet Silver zeolite and other inorganic substances with antibacterial properties or antibacterial ingredients extracted from plants.
preserver. Since the absorption of the functional film that absorbs ethylene gas is limited by the amount of use, preservatives for adsorbing ethylene gas are widely used. Packaging fruits and vegetables together with preservatives can achieve a certain purpose of inhibiting ethylene gas. Currently used preservatives often use oxidants such as potassium permanganate, gas adsorbents such as activated carbon and mineral powder, and palladium catalysts.
Coolant. Since the preservation of fruits and vegetables at low temperatures is beneficial to the preservation of freshness, the use of cold storage materials has become an important means in preservation technology. An elastic gel-like material containing a polymer obtained by polymerizing and crosslinking polyacrylic acid as a main component is a high-performance cold storage material. If you use it with a heat shield, it works better.
Other preservation methods and technologies New preservation trays. The fresh-keeping tray is obtained by heating the continuous extruded original plate (thermoplastic resin sheet) by vacuum forming and stamping. In addition to preventing fresh food from being damaged, the use of a tray also has a certain degree of thermal insulation. The so-called new tray is a molded product obtained by adding a functional film or a long fiber nonwoven fabric to an original sheet. This kind of tray adds functions such as adjusting humidity, controlling gas content, preventing mold propagation, etc. on the basis of the original function, so it can maintain the freshness of vegetables and fruits. In addition, the tray can reduce the change in the package size caused by absorbing moisture.
Radioactive sterilization. In order to reduce the influence of pathogenic microorganisms on the freshness of fruits and vegetables during storage and transportation, the vegetables and fruits may be first sterilized by radiation after picking, and then packaged and transported. At present, the United States and South Africa and other countries adopt a certain amount of fruits and vegetables under a certain intensity of radiation treatment.