Can frozen steamed buns be eaten? Will "type 1 carcinogens" be produced after being frozen for three days?

Steamed buns are a traditional fermented staple food in China. It is common for people to buy too much or steam too much and put the unfinished stuff in the refrigerator. However, there has been a rumor circulating on the Internet recently that if steamed buns are frozen in the refrigerator for more than 3 days, aflatoxin will grow. Is this true? What is aflatoxin? If you remove the moldy part of the frozen buns, can you still eat it? What are some precautions for storing food in the refrigerator?

What are aflatoxins?

Aflatoxin is a metabolite of Aspergillus flavus and Aspergillus parasiticus. It is a class 1 carcinogen with a toxicity equivalent to 10 times that of an equal amount of potassium cyanide and 68 times that of arsenic. It is extremely destructive to liver tissue. 1 mg of aflatoxin can cause cancer, and a single intake of 20 mg of aflatoxin can directly lead to death in an adult.

Aflatoxin is not a rare thing, it will "peek out" out of the blue. For example, bitter melon seeds, peanuts and other nuts, the bitter taste comes from aflatoxin produced during the mold process. There is also long-soaked black fungus. Black fungus itself does not have toxins, but after long soaking, it may deteriorate and produce similar biological toxins, or breed pathogenic microorganisms such as bacteria and fungi. Aflatoxin is also often found in dairy products and locally pressed cooking oils. Aflatoxin can even be found in unwashed chopsticks and cutting boards. This is because when we usually pick up foods with high starch content, starch is most likely to hide in the gaps between chopsticks. Once it becomes moldy, aflatoxin will hide inside; similarly, if the cutting board is not cleaned in time, the remaining food residues and moisture on it will become a good culture medium for microorganisms, especially the wooden cutting boards used by many families, the cracks on them are a shelter for microorganisms.

Will there be aflatoxin in frozen steamed buns?

So, is it true that steamed buns kept in the refrigerator for more than 3 days will breed aflatoxin? First of all, the production of aflatoxin requires conditions, which requires both the ability of the mold to produce toxins and suitable temperature and humidity. For example, assuming a relative humidity of 80% to 90%, the most suitable temperature for the production of aflatoxin is 25°C to 30°C. The temperature of the refrigerator is below 0°C or even minus 18°C, and the steamed buns are frozen. In this case, the probability of producing aflatoxin is small.

Moreover, previous experiments have confirmed that steamed buns kept in the refrigerator for more than 3 days or even more than 10 days do not produce any mold. However, although freezing steamed buns is safe most of the time, it is still recommended that you do not freeze steamed buns for more than 1 week. After all, after being frozen for a long time, the moisture in the steamed buns will be lost a lot, and the taste will not be good.

Why do frozen steamed buns become moldy?

Some friends also raised questions, why do frozen steamed buns get moldy? In fact, how long can steamed buns be stored in the refrigerator has a lot to do with the hygiene of the steamed buns themselves during operation. For example, the flour used when steaming the buns has become moldy and deteriorated, or the buns have been left at room temperature for a long time before freezing, or the buns were not sealed when they were frozen and were contaminated by being placed together with raw fish, raw meat and other foods. Similar to the above situations, it may cause aflatoxin to grow in the steamed buns during storage.

Some friends asked again, if we remove the moldy part of the steamed bun, can we still eat it? It is not recommended to eat steamed buns that have already gone moldy. Aflatoxin only needs a little bit to cause poisoning. Even if the mold is not necessarily aflatoxin, many molds are harmful to the body. Although the moldy part has been removed, the toxins are invisible to the naked eye and may have spread to other parts of the steamed bun. If you continue to eat the remaining part, you will still face certain health risks.

My friend wants to ask, then it should be okay to heat it up before eating? The answer is no, because aflatoxin is very heat-resistant and can only be broken down at temperatures above 280°C. The boiling point of water is 100°C, and our ordinary cooking methods can only heat it up to 200°C at most, so it cannot destroy aflatoxin.

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

The key is to properly store food and avoid the growth of mold toxins. At this point, we have to mention that most of us seem to have an inexplicable trust in the refrigerator, thinking that as long as we put food in the refrigerator, it will be "safe". In fact, if you don't clean the refrigerator for a long time, the inside of the refrigerator may be contaminated with Staphylococcus aureus, Salmonella, Listeria monocytogenes, Yersinia and other foodborne pathogens as food is put in.

The temperature of the refrigerator's cold storage layer is low, and bacteria will basically stop growing. However, if they are not frozen to death, they can still multiply under appropriate conditions. Moreover, among the pathogenic bacteria in the refrigerator, there is a kind of psychrophilic bacteria that should be particularly vigilant. The typical representative is Listeria monocytogenes, which has strong adaptability to the environment and can adapt to both acidic and alkaline environments from 2°C to 42°C. It does not have high nutritional requirements and can grow and multiply at food refrigeration temperatures (usually 0°C to 8°C), and can even multiply slowly below 0°C. Once a person is infected with Listeria monocytogenes, symptoms such as fever, nausea, and diarrhea may occur at the mildest, and "refrigerator enteritis" may be induced at the worst, leading to meningitis, sepsis, and so on. Food containing this bacteria can only be eaten after it is fully heated. So in the end, the editor summarizes a few points that need special attention for storing food in the refrigerator:

1. Clean and disinfect the refrigerator regularly, wipe it every few months, including various shelves and filters, to inhibit the survival of pathogens.

2. Do not store too much food and leave some space between food to avoid affecting the circulation of cold air.

3. When storing food, keep raw and cooked food separate, and store cooked food in a sealed container to avoid cross infection.

4. It is recommended to buy food before eating to avoid leftovers. If you want to put it in the refrigerator, you must cook it thoroughly before the next consumption to kill the bacteria as much as possible.

The online rumor that frozen steamed buns cannot be eaten is a false statement, but the refrigerator is not a "safe". As a storage method, it should be used scientifically and not over-reliant on. After all, fresh ingredients are the safest and most delicious!