Will steamed bread that has been frozen for too long breed "a type of carcinogen"? Warning: The refrigerator is not a "safe"

Expert of this article: Li Jiaxi, Master of Food Biotechnology, China Agricultural University

This article was reviewed by Li Lin, PhD in Food Science, Professor of Zhongshan College, University of Electronic Science and Technology of China, and food safety expert in Zhongshan City

Temperatures have soared in many places recently

Straight to 35℃!

How many friends have stockpiled supplies?

Eat less than the speed of spoiling?

Food in your home

Has it started to mold or go bad?

Copyright image, no permission to reprint

refrigerator

It is the most indispensable appliance in our daily life.

But it is also the most misunderstood

Soul Question:

How many people treat the refrigerator as a "safe"?

I believe most of you will raise your hands weakly.

Recently there is news that

Eating frozen steamed bread for a long time is unhealthy

Frozen steamed bread may produce aflatoxin

Have you heard about it? The main raw material of steamed bread is flour. The high water content of flour can easily lead to mold contamination. Aflatoxin is widely present in various grains and cereals. Aflatoxin is carcinogenic and mutagenic. If steamed bread is frozen for a long time, it will produce aflatoxin, which can cause cancer if eaten!

Can steamed buns be frozen and stored?

Which pathogens should we be most wary of during storage?

If steamed buns are also your staple food

Then you must watch

Frozen steamed bread for more than three days

Will it produce a first-class carcinogen?

Aflatoxins are produced by Aspergillus flavus and Aspergillus parasiticus in the genus Aspergillus.

The following environmental conditions are also required for the production of aflatoxin:

① The growth temperature range of Aspergillus flavus is generally 12℃-42℃, and the optimum temperature is 33℃;

②The adaptable temperature for aflatoxin production is generally between 24℃ and 28℃;

③The minimum relative humidity for adaptation is 78% RH, and the optimum humidity is 93%-98% RH.

Therefore, aflatoxin contamination is more common in humid environments with relatively high temperatures.

The temperature in the freezer of a refrigerator is generally around -18°C, the maximum humidity does not exceed 75% RH, and the average humidity is only around 50% RH. Neither the temperature nor the humidity meets the suitable conditions for the growth of Aspergillus flavus.

In addition, under freezing conditions, the life activities of microorganisms will slow down or even stop, and they will basically no longer produce toxins. Therefore, as long as the steamed buns are not contaminated before freezing and the refrigerator is clean, the possibility of aflatoxin growing again is generally low.

Copyright image, no permission to reprint

Refrigerating steamed buns can prevent aging and deterioration, reduce the activity of microorganisms and enzymes, and extend the shelf life. On the contrary, steamed buns are more likely to mold at room temperature. If you want to store steamed buns for a long time, it is recommended to freeze them.

If steamed buns are moldy, can I still eat them after removing the moldy parts?

Frugality is a fine tradition of the Chinese nation. Many people are reluctant to throw away the entire food when they see it is a little moldy, so they remove the moldy parts and continue to eat it. If steamed buns are moldy, can the parts without mold still be eaten?

The answer is: It is not recommended to eat moldy steamed buns.

This is because: many molds will produce mycotoxins under appropriate conditions. Molds are visible to the naked eye, and the surface is often gray-green, but the toxins are odorless, tasteless, and colorless, and cannot be distinguished by the naked eye. Although the moldy part is removed, the toxins may spread to other parts of the steamed bun along with the hyphae. In addition, the steamed bun itself is relatively soft and has loose holes, which makes it easier to spread.

Copyright image, no permission to reprint

So after heating it to kill the mold, can we eat it?

The answer is: No

Aflatoxin is highly heat-resistant and can only be broken down at temperatures above 280°C. Ordinary cooking and heating at a maximum of 200°C will not destroy it.

Ingestion of aflatoxin can cause acute poisoning in humans and animals. Its toxicity is mainly manifested in carcinogenicity and mutagenicity. Studies on physiological carcinogenic mechanisms have shown that aflatoxin can bind to DNA purine residues in the body, thereby causing DNA damage, changes in DNA structure and function, and cancer. Its toxicity is equivalent to 10 times that of an equal amount of potassium cyanide and 68 times that of arsenic. It is a particularly toxic substance and a strong carcinogen.

So if the steamed buns are moldy, don’t eat them to avoid increasing safety risks.

Is this actually the thing that steamed buns are most afraid of when storing them in the refrigerator?

Our biggest misunderstanding about refrigerators is that we think they are the safest places. But in fact, if they are not cleaned for a long time, the refrigerator may be contaminated with various foodborne pathogens such as Staphylococcus aureus, Salmonella, Listeria monocytogenes and Yersinia as food is put in it.

Although the temperature of the refrigerator's cold storage layer is also very low, the bacteria will basically stop growing, but they are not frozen to death. Under the right conditions, they can still reproduce.

Moreover, among the pathogenic bacteria in the refrigerator, there is a kind of psychrophilic bacteria that we should be most vigilant about. A typical representative is Listeria monocytogenes.

Copyright image, no permission to reprint

Listeria monocytogenes has a strong adaptability to the environment, ranging from 2℃-42℃, whether acidic or alkaline, and has low nutritional requirements. It can grow and reproduce at food refrigeration temperature (usually 0℃-8℃), and can even survive and reproduce slowly below 0℃.

If you do not pay attention to hygiene, once you are infected with Listeria, you may experience mild symptoms such as fever, nausea, diarrhea, etc., or severe symptoms such as "refrigerator enteritis" which may lead to meningitis, sepsis, and miscarriage in pregnant women.

Therefore, the most important thing to be wary of when storing steamed buns in the refrigerator is Listeria. Foods stored in the refrigerator and frozen foods must be completely heated before eating.

What else should we pay attention to when storing food in the refrigerator?

First: Regular cleaning and disinfection

Clean and disinfect food contact areas regularly, including various layers and filters, every few months to inhibit the survival of pathogens. Disinfect regularly, using diluted bleach or 0.1% potassium permanganate.

Second: The storage volume should not be too much

Leave some space when stacking to avoid affecting the circulation of cold air.

Copyright image, no permission to reprint

Third: Separate raw and cooked food

When storing food, pay attention to keeping raw and cooked food separate, and cooked food should be stored in a sealed manner to avoid cross-infection of bacteria.

Fourth: Be sure to heat it completely before eating

Try to buy less and eat now. Try to avoid leftovers. Let leftovers cool before storing them in the refrigerator. Cook them thoroughly before eating them next time to kill germs.

Copyright image, no permission to reprint

Fifth: These foods should not be placed in the refrigerator

Tropical fruits such as bananas and mangoes may be frozen if placed in the refrigerator, causing the skin to turn black; honey may crystallize if placed in the refrigerator, affecting the taste.

Although the refrigerator is not a "safe", there is no problem in freezing steamed buns within their shelf life.

As long as you pay attention to refrigerator hygiene in your daily life and follow the above steps, you don’t have to worry too much. Finally, I emphasize: don’t eat moldy food! Don’t eat moldy food!

The watermarked images and cover images in this article are from the copyright gallery, and the image content is not authorized for reprinting