Introduction of spontaneous modified atmosphere fi

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Introduction to spontaneous modified atmosphere film packaging for fruit preservation

packaging is an important part of transforming products into commodities. It has the effects of containing products, protecting products and promoting products. The packaging of different products also varies according to the characteristics of products. The packaging of fresh fruits provides great convenience for the circulation of fruits in the process of post harvest storage, transportation and marketing. It can keep fruit fresh, reduce wastage, prolong shelf life, attract and facilitate consumers. Therefore, good packaging not only helps to improve the transportation of fruit products between farmers and consumers, but also protects and publicizes products

in the past, the lack of proper packaging and cold chain transportation seriously hindered the sales of fresh fruits. Products in peak season are only sold in bulk at the place of origin. Health and quality protection are seldom considered, and the decay loss is quite serious. According to statistics, China's total fruit output in 1998 reached 57million tons, making it the largest fruit production and sales country in the world. However, about 30% of the fruits are lost in the process of storage, transportation and marketing, and improper packaging is one of the reasons for the loss of fruit decay. At present, in the highly competitive market conditions, the role of packaging is becoming more and more important

plastic film packaging is the most widely used packaging material for fresh fruits and vegetables. It is transparent and can clearly see the condition of the packaged products at a glance; It can reduce the moisture loss of the product and increase the freshness; It is breathable, can play the role of spontaneous air regulation, and prolong the preservation time; Its airtightness can protect products from pollution; At the same time, its low price also makes its application prospect very broad. However, the packaging requirements of different fruits also vary greatly due to their own physiological characteristics and the conditions encountered in the storage, transportation and marketing links. This paper mainly introduces map (modified at atmosphere packaging) for fruit preservation

I. physiological characteristics of fresh fruit

the fruit is a living body. It is still breathing after harvest and is carrying out vigorous life activities. The nutrition and water consumed by respiration and metabolism in the tree before fruit picking are supplemented by the branches and leaves of the tree, while the process of life is maintained by consuming its own nutrition and water after harvest. If the fruits are not kept fresh in time after harvest, shaozetian (strawberry, litchi, longan, cherry, etc.) will lose its edible value due to water loss, quality deterioration and decay in 10 days and a half months (peach, pear, grape, etc.). Although the physiological characteristics of different fruits are different, post harvest discoloration, water loss, taste change and decay are common problems. Therefore, it is a common principle that all fruits should follow in postharvest storage and preservation to reduce their respiratory intensity, inhibit their metabolic process, delay aging, reduce the consumption of nutrients, and maintain their resistance and flavor quality. Packaging is also an important part of fruit preservation

there are many ways to keep fruits fresh after harvest. Low temperature and controlled atmosphere are the most widely used storage methods in commerce at present. Because low temperature and controlled atmosphere can effectively inhibit the attraction intensity of fruits, reduce the production of ethylene, delay aging, reduce water loss, maintain the hardness and color of fruits, inhibit the growth of bacteria, and significantly prolong the storage and preservation time of fruits

II. Principle of spontaneous modified atmosphere plastic thin film packaging

spontaneous modified atmosphere thin film packaging (map) is a new type of modified atmosphere storage or sales packaging developed in recent years. It has the characteristics of transparency, permeability and moisture retention, and is widely used as the post harvest fresh-keeping packaging of fresh fruits and vegetables. Map uses the characteristics of oxygen consumption and carbon dioxide emission during self respiration after fruit is bagged and sealed to reduce the oxygen content and carbon dioxide concentration in the bag, so as to achieve spontaneous climate control. The development of map makes the marketization of many fresh fruits and vegetables faster and faster. The commercialization of map in Britain and France has reached 40% and 25% respectively

the permeability of plastic film to O2 and CO2 is different. Generally, the permeability of CO2 is greater than that of O2, and the ratio of CO2 accumulated by respiration is less than that of O2 consumption at the corresponding rate. The penetration ratio of the plastic film to O2 and CO2 depends on different resins, and most of the polypropylene resins are between 3:1 and 5:1. The success of the commercial application of spontaneous modified atmosphere plastic film packaging (map) in fresh fruit and vegetable products will be attributed to the fact that this film bag has the characteristics of controlled atmosphere balance. It can effectively control the concentration of O2 and CO2 at%, so as to effectively inhibit enzyme browning and bacterial growth and reduce water loss

III. types of spontaneous modified atmosphere plastic thin film packaging

polyethylene film bags (PE) with different densities: with strong toughness, waterproof, certain resistance to chemicals, and cheap, they are widely used in the storage and packaging of fruits and vegetables. However, different fruits should be packed in film bags with appropriate density or thickness due to their different physiological characteristics. For example, the storage effect of single fruit packed in 0.01mm film bag is very good; Cherry packed in high-density polyethylene film bags and stored at 0 ℃ for 2 months can keep the fruit stalk green and reduce weight loss and decay

the high-density film bag (p-plus) with micropores has established a consultation mechanism with the Winter Olympic Organizing Committee: it is a new type of spontaneous modified atmosphere packaging widely used in fruit storage in recent years. According to the fruit respiration intensity and physiological characteristics, it can add micropores (U) with different apertures on the film bag to enhance the gas exchange in the bag and maintain a certain proportion of O2 and CO2 concentration, Prevent O2 from being too low (<1% O2 = it causes the fruit to breathe without oxygen, and produces a large amount of volatile substances such as ethanol and acetaldehyde, which affects the flavor of the fruit. In addition, this kind of porous film bag can also reduce the humidity and volatility in the fruit. 4 Jiuzhaigou County, Aba Prefecture, Sichuan Province produces the accumulation of 7.0 earthquake metabolites, which is very suitable for humidity sensitive fruit and vegetable products, especially tropical fruits.

polyvinyl chloride film (PVC) : it is a new film which is widely used in the outsourcing of fresh fruit and vegetable products. Some PVC films (such as cellulose acetate) have strong oxygen and air permeability. They are called "breathing films". They also have good extensibility and can be closely attached to products. They are good sales packages for fresh fruit and vegetable products

other plastic films, such as polyethylene, polypropylene, polyester and hydrochloric acid rubber, can be heat shrinkable through heating tunnel. They are commonly used in fruit shrinkable packaging. They are biaxial oriented PVC films and vinyl chloride copolymers (vinyl acetate) with monomers. They are generally treated at 100 ℃ for 2 minutes

IV. problems needing attention in the application of map

due to the different physiological characteristics of different varieties of fruits and the different conditions encountered in post harvest storage, transportation and marketing, the requirements for packaging vary greatly. At the same time, fruit maturity, ambient temperature and post harvest treatment also affect the respiratory intensity of the product, thus affecting the concentration of oxygen and carbon dioxide in the packaging bag. Therefore, the following factors should also be considered when using the map

1. maintain appropriate O2 and CO2 concentrations

select appropriate film packaging bags according to the physiological characteristics of different fruits. The fruit is sealed in the map bag. If the permeability of the film bag is poor, the respiratory intensity of the fruit is too high, and the O2 concentration in the bag is too low (<3%), the fruit will have anaerobic respiration, resulting in the accumulation of volatile substances such as ethanol and acetaldehyde, producing peculiar smell and odor, and reducing the flavor quality of the fruit. In addition, high CO2 concentration (> 10%) will also cause damage to some fruits. For example, banana and yingyao can tolerate relatively high CO2 concentration, while peach, pear and citrus are sensitive to low O2 and high CO2. The recently developed high permeability microporous film enables the O2 and CO2 concentration in the bag to be maintained at 5-15%, which is conducive to the packaging of products with high respiratory intensity. Moreover, the membrane bag with micropores can increase the oxygen in the bag, reduce the humidity in the bag and the accumulation of volatile metabolites. It is very suitable for humidity sensitive fruit and vegetable products, especially tropical fruits. But this kind of packaging material is much more expensive than ordinary plastic film

2. add ethylene absorbent in the bag

some fruits release ethylene during Postharvest Ripening. The permeability of plastic film bags to ethylene is poor. The accumulation of ethylene will accelerate fruit aging, reduce fruit quality and reduce storage period. Therefore, ethylene absorbent should be added to the packaging bag of fruits that are particularly sensitive to ethylene (such as peach, cherry, kiwi fruit, tomato, etc.)

3. In combination with fungicides

although low O2 and high CO2 concentrations have a significant inhibitory effect on the pathogenicity of the pathogen causing postharvest fruit rot, the generally tolerable low O2 (> 3%) and high CO2 (<10%) concentrations in fruit physiology are not enough to kill the pathogen. After the fruit is bagged and sealed, the high temperature in the bag is conducive to the growth and reproduction of pathogenic bacteria, which often increases the degree of fruit disease. Therefore, the fruit should be sterilized before bagging, or put fungicide in the bag to reduce the occurrence of diseases

4. combined with low temperature

although spontaneous modified atmosphere plastic film packaging can play the effect of controlled atmosphere. However, high temperature will accelerate the respiration and physiological metabolism of the fruit, consume the nutrients of the fruit, reduce the quality and flavor and increase the rotten results, which will greatly reduce the fresh-keeping effect of map. Therefore, packaging cannot replace cold storage. Good packaging can maintain the best quality only under good cold chain conditions. Finally, it should be pointed out that the packaging itself can not improve the quality of fruit and vegetable products. Only after the mold structure is confirmed with high quality, can the parts of the mold be designed in detail. Good fruit and vegetable products should be packaged

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