Fresh keeping methods of hottest fruits and fresh-

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Fruit preservation methods and fresh-keeping corrugated box technology

according to the Ministry of agriculture, China's fruit output currently ranks first in the world. However, 80million tons of fruit rot in China every year, with a total loss value of nearly 80billion yuan. Among them, the most important cause of fruit decay loss is improper packaging

experts estimate that by 2010, the postpartum processing rate of fruits in China will reach about 45% to 255%. Therefore, preservation has become an important link in the fruit industry chain. The fundamental goal of preservation is to reduce the loss of postharvest decay and meet the needs of the market. This paper analyzes the factors affecting the freshness of fruits, briefly describes the commonly used fruit preservation technology at home and abroad, and briefly introduces several methods that may make the corrugated box for fruit packaging have the function of preservation. The method of coating a kind of material with fresh-keeping function on the inner surface of corrugated box is put forward, so that the corrugated box for ordinary packaging has fresh-keeping function

1 factors affecting fruit preservation

the harvested fruit is still a living organism. It is necessary to breathe continuously, breathe in oxygen, release carbon dioxide, and release heat at the same time, so that the product has the ability to resist the adverse environment and pathogenic microorganisms. These are closely related to the freshness of fruits, affecting and restricting the storage life of fruits. The factors that affect the metabolic activity and storage effect of fruits are mainly divided into external factors and the factors of the fruit itself [3]. External factors mainly include temperature, gas composition and humidity. Low temperature can inhibit fruit respiration and other metabolic processes, thereby delaying aging. On the premise of no chilling injury, the storage period should be extended by using the lowest temperature possible; Gas components also have an important impact on fruit preservation. Changing the gas composition in the surrounding environment, such as reducing oxygen content and increasing carbon dioxide content, can slow down metabolism and prolong fruit storage time; After harvest, the process of fruit absorbing water from plant roots is terminated, which can cause changes in structure, texture and surface. Therefore, maintaining a certain humidity and reducing water loss also play a key role in maintaining fruit freshness and quality

the factors of the fruit itself mainly refer to the type of fruit. The respiratory intensity of different varieties of fruits varies greatly. For example, the respiratory intensity of berry fruits is higher than that of citrus and kernel fruits, and the respiratory intensity of early maturing varieties is higher than that of late maturing varieties [3]. The amount of ripening ethylene produced by differences in respiratory intensity also varies greatly [4 - 5]. Kidd and West [4] proved that a large amount of ethylene was produced after fruit picking, and Biale also proved that the increase of ethylene accelerated the ripening and decay of fruits, which was only 0.5% one × 10 - 6 ethylene can accelerate the ripening of fruits [6]. All these show that ethylene gas can promote the aging of vegetables and fruits and accelerate the respiration. It is the decisive factor to promote fruit ripening and decay

2 commonly used fruit preservation techniques

at present, there are two main methods for fruit preservation: physical and chemical methods, which respectively control the external and self factors of fruit decay

physical methods mainly include: low temperature storage, controlled atmosphere storage, reduced pressure storage, electromagnetic radiation storage, etc. [7]. Among them, the more advanced preservation technologies mainly include critical low temperature and high humidity preservation, intercellular water structured modified atmosphere preservation, ozone modified atmosphere preservation, low-dose radiation pretreatment preservation, high-pressure preservation, cell expansion pressure control preservation, etc. Although these fresh-keeping methods are widely used, they require special equipment, complicated operation, high cost, and have certain difficulties in large-scale use

chemical methods mainly refer to preservatives. At present, common preservatives include paint coating agent, ethylene treatment agent (absorbent) [8], bactericidal and antiseptic preservative [9], etc. Among them, the paint coating agent mainly uses the effect of film covering on the surface of fruits to inhibit fruit respiration and microbial activities. The coating materials widely used in Apple preservation include sugars, proteins, polysaccharides, sugarcane lipids, polyvinyl alcohol, monoglycerides, and composite films composed of polysaccharides, proteins and lipids, as well as chitosan compounds [10], waxing, Chinese herbal medicine and other methods

ethylene treatment agents also include ethylene biosynthesis inhibitors and ethylene absorbers. Inhibitors of ethylene biosynthesis include aminoethoxyglycine (AVG), aminoacetic acid (AOA), cyclopropylenes (1 - MCP) [11]. Ethylene absorbers include activated carbon, natural zeolite, activated clay, and oxidant preparations with carrier KMnO4. Bactericidal preservatives include borax, which aims to better understand the new materials sodium carbonate, sulfur dioxide, sodium o-phenylphenol, butylamine, biphenyl, 2,4 - D, nitrogen trichloride, ammonia and amine compounds, benzimidazole fungicides, thiabendazole (TB2), Benadryl (phenylette), carbendazim and methyltobutzine. Typical inorganic fungicides include sulfite, pyrosulfate, calcium dichloride, zinc dichloride, etc

3 corrugated box for fruit packaging with fresh-keeping performance and required functions tested according to the needs of flexible packaging film

among the various methods mentioned above, physical methods have obvious fresh-keeping effect, but for fruit dealers and consumers, the cost is relatively high. Especially the more advanced physical preservation. At present, the development trend of coating preservation in chemical methods is green and environmental protection, but the excessive oil spill in this gap is not suitable for large-scale fruit preservation; Cyclopropene compounds have remarkable effect and high cost; The absorbent is mainly physical adsorption, which has the risk of desorption; Bactericidal preservatives are mostly used to spray on the surface of fruits, and the fresh-keeping effect is not particularly long. At the same time, fruits need to be fresh-keeping when they are picked and delivered to consumers, which requires a medium (i.e. packaging container or material) that is both packaged and transported and fresh-keeping. See Table 1 for the packaging containers widely used in the society at present

Table 1 types, materials and scope of application of packaging containers

tab 1 Varieties, Material and application range of packages

types of materials usage

cartons, paperboard, fruits and vegetables

plastic boxes, high-density polyethylene, any fruits and vegetables

calcium plastic boxes, polyethylene, calcium carbonate, fruits and vegetables

crates, wooden strips, fruits and vegetables

baskets, bamboo, any fruits and vegetables

reinforced bamboo baskets, bamboo skins, any fruits and vegetables

bags, natural or synthetic fibers, are not easy to scratch fruits with low water content

at present, there are mainly fresh-keeping corrugated boxes with heat insulation function, fresh-keeping corrugated boxes with gas control function and fresh-keeping corrugated boxes with overall infiltration [13]

3. 1. Fresh keeping corrugated box with heat insulation function 01. General performance

corrugated box with heat insulation function has good fresh-keeping function. This kind of corrugated box is lined with composite resin and aluminum evaporation film on the inner and outer packages of traditional cartons, or foam resin is added to the paper core. This kind of corrugated box has excellent heat insulation, which can prevent the temperature rise of the fruit itself during circulation

3. 2 fresh keeping corrugated box with gas control function

corrugated box with gas control function is to insert fresh-keeping film into the inner lining and outer lining of the box or mix porous powder that can adsorb ethylene gas in the papermaking stage. This kind of corrugated box has gas barrier property, which prevents the water evaporation of the fruit, and achieves the effect of controlling the gas content, so as to maintain the freshness of the fruit

3. 3. Fresh keeping corrugated box with integral infiltration

fresh keeping corrugated box with integral infiltration is a liquid component with Different Fresh-keeping functions infiltrated into the packaging board. After being packaged, when used to package products, the ingredients infiltrated into the packaging play different fresh-keeping roles

the overall infiltration and preservation mainly makes use of the water absorption of paper, and at the same time, the substances with preservation function are dissolved and infiltrated into the internal gap of paper. The key of this technology is to select different infiltration substances for different fruits. These substances include hydrophobic, oleophobic, antioxidant and other special substances

the three methods mentioned above have certain advantages, but a corrugated box filled with fruits can be regarded as an independent microenvironment. The corrugated box itself also has a certain heat insulation function, and the amount of oxygen inside the box is relatively lower than that outside. If we can make use of these two characteristics of corrugated boxes, we will achieve the effect of heat insulation function and gas control function at the same time to a certain extent. Using the surface coating treatment technology in the paper-making process, the preservation function can be strengthened by coating the inner surface with fresh-keeping paint. Combined with the physical preservation methods widely used at present, the preservation cycle of fruits can be effectively extended, which can not only make it possible to transport fruits with high freshness over a long distance, but also reduce the cost of fruits and the purchase cost of consumers to a certain extent

3. 4 fresh-keeping corrugated boxes with internal surface finishing

the development of fresh-keeping corrugated boxes referred to in this paper is mainly to finish the internal surface of the boxes. From the perspective of papermaking technology, this method is easy to implement in the papermaking process

this kind of corrugated box is a functional coating compounded with chemicals that can release gases with anti-corrosion function, bacteriostatic agents, and ethylene absorbers that can absorb ethylene gas, and a fresh-keeping coating is formed on the inner surface of the corrugated box by means of internal surface finishing. In the process of fruit packaging, storage and transportation, ethylene absorbent can effectively absorb the ethylene produced during respiration by absorbing the water evaporated on the surface of fruits in the carton microenvironment, and can improve the concentration of carbon dioxide to achieve the effect of air conditioning to a certain extent. The fresh-keeping coating slowly releases gas in the carton microenvironment to inhibit fruit corruption, control the metabolic rate of fruits, and inhibit the reproduction of bacteria, so as to better consolidate the effect of fruit preservation

because it only finishes the inner surface of the carton, it will not affect the strength and original function of the corrugated carton while giving the carton the fresh-keeping function. Moreover, the treatment process is relatively simple and easy to implement. Therefore, this kind of fresh-keeping corrugated carton with inner surface finishing treatment has broad development and Application prospects

4 conclusion

with the rapid development of science and technology, fruit preservation methods have tended to diversify. While pursuing low cost and high preservation effect, we should also take into account the factors of green environmental protection. While adopting refrigeration technology and other fresh-keeping methods with good fresh-keeping effect, developing and using the fruit fresh-keeping packaging carton with internal surface coating treatment being studied in this paper will play a positive role in promoting the development of fruit fresh-keeping logistics industry in China

reprinted from: Packaging Engineering

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