A New Method for Preserving Fresh 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. The demand for fruits and vegetables is getting bigger and bigger, and the demand for its freshness is getting higher and higher.

Fruits and vegetables did not die after picking, and they still retained their vitality. 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.

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 past and easily controlling the gas, but also improve the freshness of fruits and vegetables.

Ethylene Adsorption Film The ethylene adsorption film is used to remove harmful ethylene gas. The plastic film (especially LDPE) is mixed with gas-absorbing porous materials such as tuff and zeolite, clay minerals, and stone powder. It can absorb ethylene or block far-infrared radiation. The mechanism of ethylene adsorption is that the pores on the surface of the porous inorganic substance 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.

The plastic wrap used for films and fruits for preventing dew films is generally made of low-density polyethylene, polypropylene, polybutadiene, polystyrene, ethylene-vinyl acetate copolymers, and polyvinyl chloride resins having high gas permeability. film. 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 microorganisms 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.

The antibacterial thin film antibacterial film is a mixture of silver zeolite with antibacterial properties into the film, mainly using PE, PP and PS as the base material. This film can inhibit the proliferation of microorganisms to a certain extent, play a role in preservation. Silver zeolite is a mixture of sodium ions in the crystalline structure of silver and zeolite having antibacterial properties, or a mixture of silver ions and loose zeolite obtained by synthesizing aluminum and silicon as raw materials.

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 breathing speed of fruits and vegetables 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.

In the corrugated box with heat insulation function, not only the respiration of vegetables and fruits is weakened, but also the activity of microorganisms is greatly reduced at low temperatures. 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.

The Corrugated Paper Box with the function of controlling the gas will also have a certain effect on the preservation of the gas components, humidity, and other conditions, and is an important aspect of the 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 fresh-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.

Since the preservative is limited in the amount of absorption of the functional film that absorbs ethylene gas, preservatives for adsorbing ethylene gas are widely used. Packaging fruits and vegetables together with fresh-keeping 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. Because the storage of fruits and vegetables at low temperatures is beneficial to maintaining their freshness, the use of cold storage materials has become an important means of 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 freezing, it can release energy slowly. If it is used together with a heat insulation box, it can achieve a good cooling effect.

Other preservation methods and technologies

The new fresh-keeping tray fresh-keeping trays are made of 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 made by adding a functional film or a long fiber non-woven 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.

In order to reduce the influence of pathogenic microorganisms on the freshness of fruits and vegetables in the process of storage and transportation, vegetables and fruits can 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.

Source: China Packaging News