Why is it that vegetables and fruits are transported through refrigerators and can be stored at room temperature for a long time when they are taken out of the market? But they will soon break down when they are taken out of the refrigerator?
Fruits and vegetables can be transported or stored in cold storage for a long time under normal temperature. If you take it out of the refrigerator, it will break down quickly. This can be said to be a magical "fan" phenomenon, can we say that we usually use a fake refrigerator, NO!So what's the problem?Let me tell you then.
1.The freshness of fruits and vegetables is different.
First of all, we need to understand a reality: which is fresher, the fruits and vegetables sold in the market or stored in the refrigerator at home?
Someone might blurt out that it's in the fridge. Is that really the case? Generally speaking, the fruits and vegetables on the market are fresher than those bought at home because they need to be sold.
Because fruits and vegetables from the orchard or vegetable field after picking, through the cold chain storage and transportation, and then enter the market, and finally reach the hands of consumers. Of course, picking directly from fruit trees or vegetable fields and storing them in the refrigerator at home is another case.
In terms of the time when fruits and vegetables leave the matrix, the freshness of fruits and vegetables has been relatively long when they reach consumers. Therefore, in the refrigerator storage, the effect will not be very good.
2.The difference of fresh-keeping temperature
The quality of fresh-keeping of fruits and vegetables, in addition to the factors of fruits and vegetables themselves, the fresh-keeping of fruits and vegetables is closely related to the fresh-keeping temperature. Cold storage, refrigerated transportation and refrigerator storage are two different storage temperatures.
Speaking of this, some people may ask: which storage environment is more suitable for keeping fruits and vegetables fresh?
I can be responsible for telling you, of course, refrigerated transportation and cold storage. The reason is as follows: fruits and vegetables also have their own "sense" of temperature, which is determined by different physiological characteristics. The storage temperatures of some fruits are listed as follows:
①Tropical fruit temperature guide;
coconut: storage temperature 4.5 ℃;
pineapple: storage temperature 4 ~ 12 ℃;
mango: storage temperature 12.5 ℃;
②subtropical fruit temperature Manual:
banana: storage temperature 7-11 ℃;
citrus: storage temperature 7-11 ℃;
grape: storage temperature 1-2 ℃;
nectarine: storage temperature 0 ~ 1 ℃;
cherry: storage temperature 0.5-1;
red jujube: storage temperature - 2 ℃~ 1 ℃;
pitaya: storage temperature 3 ~ 6 ℃;
③temperature manual for warm temperate, middle temperate and cold temperate fruits:
Apple: storage temperature - 1 ~ 1 ℃;
pear: storage temperature 0.5 ~ 1.5 ℃;
apricot: storage temperature - 0.5 ~ 1.6 ℃;
strawberry: storage temperature 0 ℃;
Hami melon: storage temperature 3 ~ 4 ℃;
kiwi: storage temperature 0 ~ 1 ℃;
watermelon: storage temperature 10 ~ 12 ℃
Refrigerated vehicles and cold storage can provide a suitable environment for fruits and vegetables to "survive" (fruits and vegetables are still alive after picking), which is very good for preservation in their favorite low temperature environment.
On the one hand, low temperature can inhibit the respiration and microbial growth of fruits and vegetables, on the other hand, it can delay the ripening time of fruits and vegetables (mainly ethylene, which will accelerate the ripening of fruits and vegetables at high temperature).
On the contrary, the temperature range of refrigerator is as follows:
The temperature range of freezer is - 4 ℃ ~ - 24 ℃;
The temperature range of cold storage room: - 4 ℃ ~ 15 ℃.
Refrigerators store fruits and vegetables, most of the time not just one. Different fruits and vegetables stored in the refrigerator can not meet the storage temperature of each kind of fruits and vegetables.
Take mango as an example, if the temperature is higher than 13 ℃, it will accelerate the activity of mango enzyme and ethylene production, and finally lead to mango ripening. If the temperature is lower than 12 ℃, the low temperature environment will destroy the cell structure of mango pulp and cause frostbite.
The last point: the temperature difference control of fruits and vegetables in cold storage, refrigerated vehicle transportation and refrigerator storage.
The fruits and vegetables that participate in the cold chain should be pre cooled before entering the low-temperature storage environment. The cooling work should be carried out by means of air cooler, natural pre cooling or water cooling, and the general time is 24 hours.
In addition, the temperature of fruits and vegetables should be adjusted before they are put out of the warehouse, so that the temperature of fruits and vegetables and the temperature of the warehouse can be raised slowly and synchronously. In these two links, fruits and vegetables will not cause cell damage due to drastic temperature difference.
On the contrary, when stored in the refrigerator, put it directly into the refrigerator at room temperature. After a period of storage, the fruits and vegetables are removed when the temperature is close to the set temperature of the refrigerator.
The temperature difference between refrigerator and room temperature is more than ten degrees. (especially in summer) this sharp temperature difference, even in the human body, can lead to a cold. As far as fruits and vegetables are concerned, they are better than others. Fruit and vegetable cells will be damaged, leading to rot or "softening" phenomenon.
The respiration of fruits and vegetables, which needs the participation of oxygen: the refrigerator is a relatively sealed environment, and fruits and vegetables consume less oxygen in the low temperature environment of the refrigerator, but less consumption does not mean that they do not consume oxygen.
When fruits and vegetables are stored in the cold storage for a period of time, if the refrigerator can not be opened for ventilation. Then fruits and vegetables will change aerobic respiration into "anaerobic respiration". Although anaerobic respiration will reduce the amount of carbon dioxide and heat of fruits and vegetables, it will also produce a new substance - ethanol, which is commonly known as alcohol. This substance can cause the taste of fruits and vegetables to deteriorate.
In refrigerators and refrigerated vehicles, there is no need to worry. Take the air-conditioned refrigerators as an example: when fruits are stored in the air-conditioned refrigerators, the air composition of fruits participating in respiration is deliberately controlled, and ethylene removal equipment is equipped.
For example, the parameters of Apple controlled atmosphere storage are: oxygen is 3% - 5%, carbon dioxide is 1%. When the gas composition in the reservoir is out of balance, the microcomputer will adjust the gas. Generally, there is no phenomenon of anaerobic respiration in fruits.
The reproduction and growth of microorganisms are closely related to water activity aw. It refers to the proportion of water energy contained in the matrix used for microbial activities, which can be expressed as: Aw = P / P0,.
Where “P” is the partial pressure of water vapor of multi diffusive solution contained in the matrix;
“P0” is the partial pressure of water vapor of pure water at the same temperature as P.
At equilibrium, the water activity happens to be equal to 1 / 100 of the relative humidity expressed as a percentage in the surrounding air. Reducing water activity can inhibit the reproduction and growth of microorganisms. The decrease of temperature will reduce the relative humidity near the fruits and vegetables, which will lead to the surface drying of fruits and vegetables, and reduce the available water of the surface to below Aw.
Fruits and vegetables in the cold chain storage situation is like this:
Before storage to go through sterilization treatment, cold storage and refrigerated car also need to be disinfected. Coupled with the low temperature and low humidity environment inside the cold storage, the water supply for the growth of microorganisms is poor, which will inhibit the growth of microorganisms to a great extent. Create a relatively "sterile" environment.
Storage of fruits and vegetables in the refrigerator:
At the initial stage of putting fruits and vegetables into the refrigerator, there was no pre cooling in advance. Therefore, due to the large temperature difference, the low-temperature steam of the refrigerator will liquefy when it meets the fruits and vegetables with higher temperature.
That is, fruits and vegetables will be attached with a layer of water mist or droplets, which provides an excellent condition for the growth and reproduction of microorganisms. Moreover, the refrigerator is not a sterile environment. Because it is often used, even if it is disinfected, when the refrigerator is opened, microorganisms in the air will "take advantage".
At low temperature, although the growth of microorganisms will be inhibited, it does not mean that they will stop growing. When the fruits and vegetables come out of the refrigerator. With the increase of temperature, the microorganisms that lurked in fruits and vegetables began to propagate and destroy the tissue structure of fruits and vegetables. Eventually lead to the decay of fruits and vegetables!
In conclusion, under the influence of freshness, temperature difference, respiration and microorganism, the final storage effect of fruits and vegetables stored in refrigerator is not as good as that of cold chain storage. Therefore, there will be a phenomenon that "vegetables and fruits are transported by cold storage, and can be put in the market for a long time at room temperature when they are taken out of the refrigerator, and they will soon break down".
The above is the reason why the fruits and vegetables stored in the refrigerator will rot when they are taken out, and the fruits and vegetables transported through the cold storage and refrigeration will not rot rapidly at room temperature. If you have different opinions, please feel free to contact with us.