"Health from eating" series | Will leafy vegetables left in the refrigerator for 24 hours cause cancer? Help you distinguish the truth

The refrigerator can not only preserve the freshness of food, but also prolong the edible time to a certain extent. Recently, a video titled "Several Foods That Should Never Be Refrigerated" has been circulated on the Internet. In the video, the host said: "Eating black fungus that has been soaked in the refrigerator for two days will cause poisoning", "When potatoes are placed in the refrigerator, starch is easily converted into polysaccharides under low temperatures, and some of these polysaccharides can cause poisoning", and "Leafy vegetables placed in the refrigerator for 24 hours will produce a large amount of nitrite, which can cause cancer if eaten."

In addition to the several refrigerator food storage rumors mentioned in the video, there are also widely circulated sayings on the Internet such as "Washing eggs and putting them in the refrigerator can extend the shelf life" and "Putting the fruits you bought in the refrigerator will prevent them from spoiling easily". So, are these sayings true or false? Let's analyze them in detail today.

Rumor 1: Eating black fungus that has been soaked in the refrigerator for two days will cause poisoning

Analysis: False. Soaking in the refrigerator for two days is not the root cause of fungus poisoning.

In recent years, poisoning incidents caused by eating black fungus have occasionally occurred. The reason is that the black fungus is soaked in an improper way. When soaking black fungus, if the container is not clean, the room temperature is high, the soaking time is long, and the water is turbid and the black fungus is sticky, there is a considerable risk of poisoning if it is eaten as it is.

The poisoning is caused by the toxin fumonisin, which is a metabolite produced by the crazy growth of Pseudomonas cerebrovenenans. It is highly toxic and there is no specific medicine. The average mortality rate of poisoning cases can be as high as over 50%.

It may be produced during the soaking process of black fungus, but it is most likely not produced during the soaking process in the refrigerator, but before it is put into the refrigerator, especially in the hot summer. This is because this fungus likes to grow at 37℃, the best temperature for toxin production is 26℃, and the temperature of the refrigerator is usually 0-4℃.

The temperature is high in summer, so it is recommended to soak black fungus:

① Clean the surface of the fungus, use a clean container and water, and soak it in the refrigerator for about 3-4 hours. The fungus will be larger in size and have a more elastic taste.

② Soak as much as you want to eat, and eat it as soon as possible after soaking. Do not store it in the refrigerator for more than 24 hours after soaking. If you cannot finish it, it is recommended to pack it in fresh-keeping bags and store it in the freezer to minimize the risk.

③During the soaking process, if you find that the surface is sticky, soft or has an odor, discard it decisively.

Myth 2: Potatoes are high in starch and will produce polysaccharides in the low temperature environment of the refrigerator, some of which can cause food poisoning

Analysis: False.

Under low-temperature storage conditions, potato starch will decompose and convert into sugar. The so-called sugar is a normal "saccharification" phenomenon, which directly brings a sweet taste, but it is not toxic.

Instead of worrying about the impact of low-temperature storage, it is better to pay more attention to sprouted potatoes. Sprouted potatoes contain high levels of toxic alkaloids - solanine, which may cause poisoning if eaten by mistake.

In fact, potatoes have a small amount of solanine, which is a self-protection mechanism to prevent them from being eaten by insects. However, the content of solanine in mature potatoes is extremely low, not enough to cause harm to the human body. If potatoes are stored in a high temperature and sunny place, they will easily sprout or turn green on the skin. At this time, the solanine content in potatoes will greatly increase. Eating too much will easily turn them into "toxic" killers, causing symptoms such as vomiting, abdominal pain, and diarrhea.

In theory, although heating and using vinegar can decompose solanine to a certain extent, there is no guarantee that it will be completely decomposed. To be on the safe side, it is recommended to throw it away directly.

In addition, potatoes like low temperatures. If you want them to taste good and last longer, they should be kept at low temperatures and away from light, otherwise they will easily sprout and turn green. For potatoes bought in summer, it is recommended to put them in opaque bags, store them in the refrigerator, and eat them as soon as possible.

Rumor 3: Leafy vegetables should not be kept in the refrigerator for more than 24 hours, otherwise they will easily produce a large amount of nitrite, which can cause cancer if eaten

Analysis: False. In fact, the nitrite produced by leafy vegetables at room temperature is higher than that of refrigerated vegetables.

Leafy vegetables contain a certain amount of nitrate, which can easily be converted into nitrite to a certain extent; if excessive nitrite is consumed, it will be converted into nitrosamines in the body, which will increase the risk of cancer.

Take spinach as an example. If fresh spinach is directly stored in a refrigerator at 4°C, the refrigeration time should not exceed 3 days. Even if it is fried and refrigerated, its nitrite content may exceed the prescribed standard (nitrite content in vegetable products should be less than 20mg/kg) after 16 hours. So it is best to eat all the spinach at once.

So, how to reduce the harm of nitrite in vegetables?

① Eat fresh leafy vegetables.

② Blanching leafy vegetables: Blanching in boiling water can remove most of the nitrate and nitrite components.

③ Eat immediately after cooking: Cook as much as you want to eat. If you cook too much, pack it in advance and refrigerate it immediately to reduce bacterial growth. It is not recommended to eat cooked food if it is left at room temperature for 2 hours or refrigerated for more than 24 hours.

④ Follow the principle of “try not to leave any leftovers and eat them up as soon as possible”.

Myth 4: Washing eggs before putting them in the refrigerator keeps them clean and prolongs their shelf life

Analysis: False. Washing eggs in advance and putting them in the refrigerator may shorten their shelf life and contaminate kitchen utensils in the process.

If you buy clean eggs with packaging, just store them in the refrigerator together with the packaging. If the loose eggs bought from the vegetable market are covered with chicken feathers and chicken droppings, many people can't help but wash them, but washing them will destroy the protective film of the eggshell itself.

The egg shell has a layer of gelatinous film - "white frost", which not only covers the pores on the surface of the eggshell, but also resists the invasion of microorganisms such as bacteria, and prevents the evaporation of water inside the egg.

Direct water washing will destroy the integrity of the gelatinous membrane, breaking the line of defense against external pollution. Microorganisms and other pathogens may directly enter the eggs through the pores and contaminate the eggs. In addition, the water content of the eggs will also be lost, and they will easily deteriorate over time.

The correct way to do it is, if you can't finish the eggs you bought in a short time, it is best not to wash them with water first. If you are afraid of getting them dirty, you can "dry clean" them, such as wiping them with a dry cloth, dry sponge or paper towel, putting them in a plastic bag, sealing them and refrigerating them, and then wash them before eating.

Rumor 5: Put all the fruits you buy in the refrigerator so they don’t spoil easily

Analysis: False. Some fruits just don’t like to be in the refrigerator.

You can’t put all the fruits you buy into the refrigerator at once. Not all fruits can be placed in the refrigerator. You need to analyze the specific situation.

The refrigeration temperature of the refrigerator is usually set at 4°C, which is conducive to preserving freshness.

However, it is not a universal safe, the following fruits are not suitable for storage in the refrigerator:

Fruits that cannot be refrigerated before they are ripe: bananas, pineapples, avocados, passion fruit, mangoes, kiwis, and papayas. These fruits take some time to ripen, and if they are not fully ripe, they are not suitable for the refrigerator.

Citrus fruits: These fruits also don’t like the refrigerator. Lemons, grapefruits, and oranges are prone to cold damage, so they can be stored directly at room temperature.

Fruits like longan, pomegranate, and carambola can be kept for a long time at room temperature, but are more likely to suffer from cold damage if kept in the refrigerator.

in conclusion

The refrigerator is not a universal safe, and there are certain rules to follow when storing vegetables and fruits. In summer, it is recommended to soak black fungus in a clean container in the refrigerator. Eat it as soon as possible after soaking, and do not store it in the refrigerator for more than 24 hours; potatoes stored in the refrigerator at low temperature will not cause food poisoning; vegetables and fruits should adhere to the "three current" principle of eating now, buying now, and cooking now, which can effectively avoid food safety risks.

Reviewer: Zhong Kai, Director of Kexin Food and Health Information Exchange Center