"A red dust concubine laughs, no one knows that it is Lychee." Many people must have heard this allusion. During the Tang Dynasty, Yang Guifei liked to eat lychees, and at that time she could only send people to send them from the south.
With the development of logistics, we can now eat fruits and vegetables from all over the world almost anytime, anywhere, and in the north, we can also eat lychees, mangoes and other tropical fruits and vegetables.
However, as the fruits and vegetables we can buy become more and more abundant, how to preserve them has become a concern for many people. Recently, there have been hot searches on the Internet indicating that not all ingredients are suitable for the refrigerator.
In addition, it is often said that tropical fruits live in the tropics, so they are more afraid of cold, can not be stored in the refrigerator, easy to occur cold damage, it is best to put outdoors. So are these claims true?
Focus
1. For home storage, fruits and vegetables are best placed in the refrigerator;
2. Do not keep fruits and vegetables in the refrigerator for more than a week;
3. When eating, eat the fruits and vegetables that are put in the refrigerator first;
4. Separate ethylene-producing fruits and vegetables from ethylene-sensitive fruits and vegetables, please refer to the figure below;
5. First eat fruits and vegetables that are susceptible to cold damage, such as cucumbers (at 2 °C, about 9 days), ripe bananas (at 7.2 °C, 6~12 days);
6. Buy fruits and vegetables at home, such as bananas, mangoes, avocados, papayas, kiwis, plums, apricots, peaches, tomatoes, etc., if not ripe, it is best to put them outdoors for 1~2 days, and eat them as soon as possible after ripening; If you can't finish eating, you should still put it in the refrigerator as soon as possible to refrigerate it.
What's going on with cold damage?
Chilling Injury refers to the damage caused by some cold-sensitive plants in a low temperature environment above the freezing point of the tissue, mainly manifested as the wrinkling, depression, lignification, and browning of the flesh of the fruit. Cold damage can cause damage to the internal structure of fruits and vegetables, loss of nutrients, and decline in disease resistance and storage tolerance, which in turn leads to deterioration and rot of fruits and vegetables.
The cold damage of fruits and vegetables is very complex, which is related to the variety, origin, storage temperature, ripeness of fruits and vegetables, temperature and humidity of the storage environment, gas composition and so on. In the commercial storage of fruits and vegetables, there are corresponding treatment requirements such as temperature and humidity for fruits of different origin, time and maturity.
Generally speaking, fruits and vegetables originating in the tropics or subtropics are more sensitive to low temperatures, and cold damage symptoms are more likely to occur in the low temperature environment under non-freezing temperature, for example, most tropical fruits and vegetables, such as bananas, mangoes, lychees, longans, cucumbers, green peppers, etc., may occur cold damage during low temperature storage and transportation. This is why it is often said that tropical fruits should not be refrigerated as much as possible.
According to relevant statistics, the loss caused by low temperature and cold damage in the fruits and vegetables sold in the mainland accounts for about 30% of the total storage and transportation of fruits and vegetables, causing great waste and losses. Therefore, the postharvest storage and transportation of fruits and vegetables has always been a key research field.
Can't you put it in the refrigerator?
It is often said on the Internet that tropical fruits are best not to be placed in the refrigerator, and it is easy to appear cold damage. Is it true?
In fact, for ordinary families, there is no need to be too entangled, and directly putting the refrigerator is still the best, most realistic and most convenient choice.
First, the cold damage of fruits and vegetables usually occurs in a long-term low-temperature storage environment, such as common fruits and vegetables, which may take more than 7 days, or even dozens of days before cold damage. Cold damage is mainly in commercial process storage, to know that the storage of commercial fruits and vegetables is often a few months or even more than a year.
Everyday families generally take about a week, and a little longer than half a month, usually don't worry too much about cold damage.
Common cold injury time of fruits and vegetables
Longan: Cold damage occurs on the 14th day of storage.
Lychee: 1 °C is 20 days of cold damage, but the good fruit rate is 90%; 5 °C storage for 30 days cold damage; There are also studies on 5 varieties of lychees stored at different low temperatures, and the results found that at 1~5 °C, the shortest can be stored for about 25 days.
Cantaloupe: The situation varies by species. "Karakusai" Cold damage occurs after storage at a low temperature of 0~2°C for 40~50 days. "86-1" cantaloupe fruit stored at 1 °C for 14 days After moving to room temperature for 3 days, small light brown spots appeared in the peel; Cantaloupe fruits stored at 3°C showed mild symptoms of cold damage for 42 days, and no water-soaked conditions were found.
Mango: Kent mango will have cold damage symptoms when stored at 13°C for 10 days; Purple flower mango was stored at 2 °C for 15 days and 5 °C for 34 days, and no cold damage occurred when stored at 8 °C for 34 days.
Sweet potato: the cold damage time of sweet potato storage at 1 °C is about 9 days, and the critical point of cold damage of sweet potato storage at 4 °C is about 45 days.
Green pepper: After 1 week of storage at 2 °C, cold damage occurs, and a few very small depression spots appear in individual fruits.
Nectarine: Cold damage can be induced at 3 °C, 5 °C and 7 °C, of which 5 °C has the strongest cold sensitivity, followed by 3 °C, and 7 °C is the slowest. The storage period at 1 °C can be about 40 days.
Guangdong sweet orange: stored at 1~3 °C for 4~5 months, the brown spots caused by low temperature damage are much lighter than in storage at intermediate temperature (7~9 °C).
Cucumber: Cold damage symptoms of different sizes of depression spots or water-stained spots appear on the melon surface after storage at 0 °C for 3 days, but at 2 °C, there are minor cold damage symptoms for about 9 days.
Bananas: unripe bananas, put for a few hours may be cold damage, for example, some studies have found that the harvested fresh lagadan bananas, at 1.1 °C for 2 hours began to appear cold damage phenomenon, at 7.2 °C for 4 hours cold damage symptoms; but after ripe, storage for 6~12 days when moderate cold damage symptoms.
Second, compared with the normal temperature environment, low-temperature storage still has great advantages, especially short-term storage.
Compared with room temperature, especially in hot summer, low-temperature freezing can significantly reduce the respiratory intensity of harvested vegetables, reduce nutrient loss, and inhibit pathogenic microbial activity. Instead of not putting the refrigerator and putting it outdoors, but also fighting insects and bacteria, refrigerator refrigeration is obviously better, which can extend the preservation time of fruits and vegetables.
In fact, the USDA's recommendation to consumers is that only a very small number of fruits and vegetables can be placed at room temperature, and most fruits and vegetables should be stored in the refrigerator. Ideally, when storing in the refrigerator, pay attention to the location so that ethylene-producing fruits and vegetables are kept at a certain distance from ethylene-sensitive fruits and vegetables.
How to use the refrigerator scientifically?
Here are 5 tips for storing fruits and vegetables in the refrigerator.
01
Refrigerate fruits and vegetables
Preferably no more than a week
If conditions permit, fresh fruits and vegetables are of course the best, with good taste and high nutrition. But now that everyone usually has to go to work, it may not be practical to buy fresh ones every day. However, I recommend that if there are no special circumstances, try not to keep the fruits and vegetables in the refrigerator for more than a week. Go to the supermarket, wet market once a week and renew the vegetables and fruits in the refrigerator. Generally speaking, within a week, most fruits and vegetables will not appear cold damage.
02
Pay attention to the order
Put it in the refrigerator first, eat first
Every time you buy fruits and vegetables, you may wish to remember the time, and put it in first to eat it first, so as to ensure that the food in the refrigerator can be updated smoothly, and some fruits and vegetables will not be put for too long.
03
Fruits and vegetables are placed separately
It is recommended to separate ethylene-producing fruits and vegetables from ethylene-sensitive fruits and vegetables. In addition, you can see cucumbers, oranges, tomatoes and other common fruits and vegetables that are easy to cold damage, and they are also recommended to be placed in the refrigerator.
04
Eat first
Fruits and vegetables that are susceptible to cold damage
For fruits and vegetables that are prone to cold damage, such as cucumbers, compared with other fruits and vegetables, they should be eaten as soon as possible and given priority compared to other fruits and vegetables.
05
Buy home unripe
The fruits and vegetables are put like this
Buy fruits or vegetables at home, such as tropical fruits bananas, mangoes, avocados, papayas; non-tropical fruits kiwi, plums, apricots, peaches, etc.; Vegetables such as tomatoes, etc., if not cooked, it is best to put them outdoors for 1~2 days, and eat them as soon as possible after ripening; If you can't finish eating, you should still put it in the refrigerator as soon as possible to refrigerate it.
Source: People's Network Science Popularization
Comprehensive: Popular Science China