Spontaneous modified atmosphere film packaging for fruit preservation

Packaging is an important part of converting a product into a product. It has the functions of containing products, protecting products, and promoting products. The packaging of different products also varies according to the characteristics of the product. The packaging of fresh fruit is a fruit that provides great convenience in circulation during storage, transportation, and marketing. It can keep fruits fresh, reduce losses, extend shelf life, and attract and facilitate consumers. Therefore, good packaging not only helps improve the transportation of fruit products between farmers and consumers, but also protects and promotes products.
Previously, due to the lack of proper packaging and cold chain transportation, sales of fresh fruit were severely hampered. Season products are only sold in bulk at the production site. Rarely consider the protection of hygiene and quality, and the loss of rot is quite serious.
According to statistics, China's total fruit production in 1998 reached 57 million tons, making it the world's largest fruit producer and seller. However, about 30% of the fruits are lost during storage, transportation, and marketing. Among them, improper packaging is one of the causes of fruit rot loss. At present, the role of packaging is becoming more and more important under the fiercely competitive market conditions.
Plastic film packaging is the most widely used packaging material for fresh fruits and vegetables. It is transparent and can clearly indicate the condition of the packaged product; it moisturizes, it can reduce the moisture loss of the product and increase the freshness;
Breathable, it can play a role of spontaneous air conditioning, extend the preservation time; its tightness, can protect the product from pollution; at the same time low price, but also makes it a very broad application prospects. However, the requirements of different fruits for packaging also vary greatly due to their own physiological characteristics and the conditions encountered in the storage, transportation, and marketing links. This article focuses on fresh-keeping, spontaneously modified, modified atmosphere packaging (MAP-Modified At-
Mosphere Packaging).
First, the physiological characteristics of fresh fruit The fruit is a living body, still breathing after harvest, carries out a vigorous life activities, the nutrients and water consumed by the respiratory metabolism in the tree before the fruit is picked are supplemented by the branches and leaves of the tree, and the Afterwards, it uses its own nutrition and water to sustain its life. If the fruit is not fresh-keeping in time after harvest, at least 3
For five days (strawberries, lychee, longan, cherries, etc.), as many as 10 and a half months (peach, pear, grape, etc.) will lose water, wilting, deteriorate, and decay and lose their food value. Although the physiological characteristics of different fruits are different, post-harvest discoloration, dehydration, malodor, and rot are common problems. Therefore, as soon as possible after harvest, the fruit reduces its respiratory intensity, inhibits metabolic processes, delays aging, reduces the consumption of nutrients, and maintains the fruit's resistance and flavor quality. This is a common principle that should be followed for all fruits after storage. Packaging treatment is also an important part of fruit preservation.
There are many methods for keeping fruits fresh after harvest. Low temperature and atmosphere are the most widely used storage methods in commercial applications. Because low temperature and modified atmosphere can effectively inhibit the attractive strength of fruits, reduce ethylene production, delay aging, reduce water loss, maintain fruit hardness and color, inhibit the growth of bacteria, and thus significantly prolong the storage time of fruit.
Second, the principle of self-adhesive plastic sheet film packaging Spontaneous atmosphere modified film packaging (MAP) is a new type of air-conditioning storage or sales packaging developed in recent years, it has the characteristics of transparency, breathability and moisture, was Widely used as post-harvest fresh-keeping packaging for fresh fruits and vegetables. MAP is the use of fruits to seal the bag and breathe after itself to consume oxygen and emit carbon dioxide, reduce the oxygen content of the bag and increase the concentration of carbon dioxide, to achieve the role of spontaneous atmosphere. MAP
The development of many new fruits and vegetables has become more and more market-oriented. The degree of commercialization of MAP in Britain and France has reached 40% and 25%, respectively.
The permeability of plastic film to O2 and CO2 is not the same. Generally, the permeability of CO2 is greater than that of O2. The ratio of CO2 accumulated by respiration is smaller than the rate of O2 consumption of corresponding speed. Plastic Films for O2 and CO2
The penetration rate depends on different resins, most of which are between 3:1 and 5:1. The success of the commercial use of spontaneously modified plastic film packaging (MAP) in fresh fruit and vegetable products will be attributed to the gas balance properties of this film bag, which effectively control O2 and CO2 concentrations to 3-10%. ,
This effectively inhibits enzyme browning and bacterial growth, reducing water loss.
III. Types of spontaneously modified atmosphere plastic film packaging Polyethylene film bags (PE) with different densities: They have strong toughness, waterproofness, certain resistance to chemicals, and are cheap. They are widely used in fruits and vegetables. Storage packaging. However, due to the different physiological characteristics of different fruits, different types of fruit should be packaged in a film bag with a suitable density or thickness. For example, citrus fruits with a 0.01mm film bag have good storage and storage; cherries are packed in high-density polyethylene film bags.
Storage at 0 °C for 2 months can keep the stem green well, reducing weight loss and decay.
High-density microporous membrane bags (p-plus): These are new types of spontaneous modified atmosphere packaging that have been widely used for fruit storage in recent years. It can add micropore (20-100u) with different pore diameters on the film bag according to the respiration intensity and physiological characteristics of the fruit in order to strengthen the gas exchange inside the bag and maintain a certain proportion of O2 and CO2.
Concentrations that prevent O2 from being too low (<1% O2) lead to anaerobic respiration of the fruit, resulting in the accumulation of large amounts of volatile substances such as ethanol and acetaldehyde, which affect the flavor of the fruit. Moreover, this porous film bag also reduces the accumulation of moisture and volatile metabolites within the patch, making it ideal for moisture-sensitive fruit and vegetable products, especially tropical fruits.
Polyvinyl chloride film (pvc): A new film that is now widely used in the sourcing of shallow trays for fresh fruit and vegetable products. Some PVC films (such as cellulose acetate) have strong oxygen permeability and water vapor permeability. They are called “respiratory films”. They have good extensibility and can be tightly attached to products. They are fresh fruits and vegetables products. Very good sales packaging.
Other plastic films, such as polyethylene, polypropylene, polyester, and chlorinated rubber, etc., can also be heat-shrinkable through heating tunnels. They are often used for fruit shrink packaging and are biaxially oriented films of PVC and vinyl chloride copolymers with monomers (acetic acid Vinyl ester) is generally treated at 100°C for 2 minutes.
Fourth, the application of MAP to pay attention to the problem Because different varieties of fruit their own physiological characteristics of different, and in the post-harvest storage, transportation, marketing, the conditions encountered in the link are not the same, the packaging requirements vary greatly. At the same time, factors such as fruit maturity, environmental temperature and post-harvest treatment also affect the respiratory intensity of the product, which affects the oxygen and carbon dioxide concentrations in the package. Therefore, the following factors should also be taken into account when using MAp.
1. Maintain appropriate O2 and CO2 concentrations Select the appropriate film packaging bag based on the physiological characteristics of the different fruits. The fruit is sealed in the MAp bag. If the air permeability of the bag is poor, the fruitful breathing intensity is too high, and the O2 concentration in the bag is too low (%). The fruit will produce anaerobic respiration, leading to volatiles such as ethanol and acetaldehyde. Accumulation of substances produces odors and odors that reduce the fruit's flavor quality. In addition, high CO2 concentrations (>10%) can also cause damage to certain fruits. For example, bananas and cherry trees can tolerate relatively high CO2 concentrations, while peaches, pears, and citrus fruits are sensitive to low O2 and high CO2. Recent development of highly transmissive microporous membranes making O2 and CO2 within the bag
The concentration can be maintained at 5 to 15%, which is beneficial to the packaging of products with greater respiratory intensity. In addition, microporous membrane bags can increase the oxygen in the bags and reduce the accumulation of humidity and volatile metabolites in the bags. This is very suitable for moisture-sensitive fruit and vegetable products, especially tropical fruits. However, such packaging materials are much more expensive than ordinary plastic films.
2. Adding ethylene absorbent in the bag Some fruits must release ethylene during post-harvest ripening. The plastic film bag has poor permeability to ethylene. The accumulation of ethylene will accelerate fruit senescence, reduce the quality of the fruit, and reduce the storage period. Therefore, ethylene absorbents should also be added to the bags that are particularly sensitive to ethylene (such as peach, cherry, kiwi, and tomatoes).
3. Combination with fungicides Although low O2 and high CO2 concentrations have a significant inhibitory effect on the pathogenicity of pathogenic bacteria that cause fruit post-harvest rot, the low O2 (>3%) and high CO2 that the fruits are generally physiologically tolerant (The concentration is not enough to kill the germs. After the fruit is bagged and sealed, the high temperature in the bag is conducive to the growth and reproduction of pathogens, and often increases the degree of disease of the fruit. Therefore, the fruit should be sterilized before bagging, or in the bag. Put bactericides to reduce the occurrence of diseases.
4. Cooperate with low temperature Although spontaneous air-conditioning plastic film packaging can play the role of air conditioning. However, high temperature results in faster respiring and physiological metabolism of fruit, consumption of male nutrients, reduction of quality flavor and increase in rot will greatly reduce the preservation effect of MAP. Therefore, packaging does not replace refrigeration, and good packaging maintains the best quality only under good cold chain conditions.
Finally, what needs to be put forward is that the packaging itself cannot improve the quality of the fruits and vegetables. Only the good quality fruits and vegetables should be packaged.