New method for fresh-keeping packaging of fruits and vegetables

With the development of economy and the improvement of living standards, people's dietary life has shifted from the past single-subsistence mode to the current diversified nutrition type. The demand for fruits and vegetables is getting bigger and bigger, and the demand for its freshness is getting higher and higher. A variety of preservation technologies and materials have been developed.

Unlike other foods, fruits and vegetables did not die after picking and they still lived. Traditional fruit and vegetable packaging, whether it is corrugated boxes or mesh bags, woven bags and cling film, can not achieve the effect of preservation. At present, a variety of functional plastic wraps, new corrugated cartons and functional preservatives have been developed, and some technologies and materials have been applied. Since these fresh-keeping materials and technologies often have a single function, in order to achieve the best preservation effect, it is sometimes necessary to use a variety of preservation technologies and materials at the same time.

Functional cling film

Although the traditional film can play a role in packaging, has a certain effect of preservation, but obviously can not meet the preservation needs of the modern market, therefore, a large number of new cling film was 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 materials such as tuff and zeolite, clay minerals, stone powder and other fine powders. Most of them can absorb 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 addition amount of gas adsorbent is 3%-5%, because the adsorption capacity of ethylene gas is limited.

Anti-dew film

The cling film used for fruits and vegetables is generally a film made of a resin such as low-density polyethylene, polypropylene, polybutadiene, polystyrene, ethylene-vinyl acetate copolymer, and polyvinyl chloride. However, when the water vapor generated from the films and fruits of fruits and vegetables is condensed on the inner surface of the film, not only the transparency thereof is deteriorated, but also the water droplets gather, so that the bacteria proliferate quickly and the fruits and vegetables are corrupted. It is the dew-proof film that can solve this problem. The dew-proof film is a surface treatment agent that treats the inner surfaces of the above-mentioned materials such as polyethylene, polypropylene, and polystyrene, absorbs excess moisture, and can appropriately maintain the humidity inside the package so as to achieve the purpose of keeping freshness.

Antibacterial film

The antibacterial film is a mixture of silver zeolite with antibacterial properties. The silver zeolite is a mixture of sodium ions in the crystal structure of silver and zeolite having antibacterial properties or a mixture of silver ions and loose zeolite synthesized by 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.

Selectively through the film

If there is no oxygen in the package, the respiration of fruits and vegetables will stop, and the fruits and vegetables will rot and deteriorate. With too much oxygen, the speed of breathing of fruits and vegetables will accelerate, and it will also accelerate the withering of fruits and vegetables. Therefore, controlling the permeability of oxygen and carbon dioxide in packaging is a very effective technology that can be used in conjunction with gas conditioning technology. In the past, selective transmissive films were mostly made by adding silicon windows to common packaging bags. The current advanced method is to add organic silicon materials to synthetic resins and directly produce transmissive film products.

Fresh-keeping corrugated carton

Corrugated cartons are currently used as containers for the transport of goods between consumption and production. Some functional corrugated cartons can be used for the preservation of fresh fruits and vegetables and have attracted great attention.

Corrugated cardboard box 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 paper box with control gas function

Adjusting the stored gas composition, humidity and other conditions will also achieve a certain degree of preservation, which is an important aspect of preservation technology.

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 cooling agents

In order to enhance the preservation effect of fruits and vegetables, at the same time as using the above-mentioned packaging materials, substances with specific functions, such as fresh-keeping sheets, preservatives and cooling agents, may be added.

Fresh-keeping 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 are multilayer structures composed of high water-absorbent resin and non-woven fabrics, thin paper, and water-absorbing polymers; the absorption of ethylene gas mostly utilizes the porosity of activated carbon; the antibacterial property is due to the addition of silver to the sheets. Zeolites 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

Because the preservation of fruits and vegetables at low temperatures is beneficial to maintain their freshness, the use of cold storage materials has become an important means in preservation technology. The elastic gel-like material mainly composed of ultra-high molecular weight sodium polyacrylate or a graft polymer thereof is a high-performance cold storage material. After being frozen, it can release energy slowly. If it is used together with a heat insulation box, it can get a good cooling effect.

Other preservation methods and technologies

New storage tray

Fresh-keeping trays are made from thermoplastic sheets 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 type of tray is a molded product obtained by adding a functional film or a long fiber nonwoven fabric to a thermoplastic sheet. This kind of tray adds functions such as adjusting humidity, controlling gas content, and preventing mould from multiplying on the basis of original functions, so it can maintain the freshness of vegetables and fruits.

Radiation sterilization

In order to reduce the impact of pathogenic microorganisms on the freshness of fruits and vegetables during storage and transportation, the fruits and vegetables may be 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.