This article is transferred from "Food Laboratory Services"
Steamed buns are a staple food that almost every family must eat, and it is common to keep them in the refrigerator if you can't finish eating them. However, there has been a rumor circulating on the Internet that steamed buns will breed aflatoxins if they are frozen in the refrigerator for more than 3 days. What is the truth?
Will steamed bread freeze produce first-class carcinogens?
Let's start with aflatoxin, which is produced by Aspergillus flavus and Aspergillus parasiticus in the genus Aspergillus. Bitter nuts, yellowed rice, and darker vegetable oils can all harbor aflatoxins.
- Aflatoxin contamination is more common in humid and relatively hot environments. The temperature of the freezer compartment of the refrigerator is generally -18°C, and the maximum humidity does not exceed 75%RH. Therefore, neither the temperature nor the humidity can meet the requirements for the growth of Aspergillus flavus.
- In addition, under freezing conditions, microbial life activities will slow down or even stop, and basically no more toxins will be produced, as long as the steamed bread is not contaminated before putting it in the refrigerator, and the refrigerator is clean, it is unlikely that Aspergillus flavus will grow.
Environmental conditions for aflatoxin production:
(1) The growth temperature range of Aspergillus flavus is 12°C~42°C, and the optimal temperature is 33°C.
(2) The adaptation temperature of Aspergillus flavus is 24°C~28°C.
(3) The minimum relative humidity is 78%RH, and the optimal humidity is 93%~98%RH.
Is it better to freeze or refrigerate?
Starchy foods like pasta can last for a day or two at room temperature. If it is stored in the refrigerator, the starch will regrow and age, and the longer it is stored, the harder the pasta will be. For example, if you take out the steamed buns in the refrigerator and steam them, you will feel that the skin of the buns will become thicker and the taste will become harder.
At the same time, starch retrogrowth and aging will not only make pasta lose its original quality, but may even cause food quality deterioration. This is because anaerobic bacteria and molds are more active in refrigerated environments. While this change can also occur at room temperature, it can occur more quickly in refrigerated environments with low temperatures and high humidity.
Generally speaking, the way to prevent starch regrowth and aging in pasta is to cool and dry quickly, that is, the steamed pasta is cooled and put directly into the freezer, and then taken out to heat it when eating.
However, frozen pasta is often not as gluten or fluffy as freshly steamed pasta when eaten, mainly because the moisture in the pasta will freeze during the freezing process, destroying the internal tissue structure, so that the pasta cannot be restored to its original state after thawing, resulting in the loss of the original quality of the pasta. In particular, cryopreservation, the damage to the gluten structure of the protein is relatively more pronounced than that of refrigeration.
It is recommended that everyone eat homemade pasta frozen in the refrigerator, do not thaw when reheating, and cook it directly, which can prevent the poor taste of frozen pasta to a certain extent. Refrigeration of steamed bread can prevent aging and deterioration, reduce the activity of microorganisms and enzymes, and prolong the shelf life. If you want to keep the steamed bread for a longer time, it is recommended to freeze it.
Don't put steamed buns directly in the refrigerator! Do 3 more steps without doing anything hard
The steamed bread is directly placed "naked" in the refrigerator, which is easy to cause the loss of moisture, and the steamed bread is dry and hard for a long time. Not to mention that it is not delicious, it may also be contaminated by other substances in the refrigerator, resulting in spoilage.
After steaming, put the steamed buns in the refrigerator?
It is recommended to steam it before putting it in the refrigerator. Because of yeast-made pasta such as steamed buns and flower rolls, the yeast in the dough below will lose its activity when stored at low temperature, and the next time you take it out and steam it again, it will affect the taste.
The steamed steamed buns must be cooled
The steamed steamed buns are naturally cooled before being put in the refrigerator, which can not only keep the steamed buns unchanged from smelling, but also avoid frosting in the refrigerator.
Before putting it in the refrigerator, the steamed buns should be wrapped and tightly sealed
It is recommended that each steamed bun should be packed in a fresh-keeping bag, and try to squeeze out the air inside before sealing it tightly. These two points must be done well, otherwise the moisture in the steamed bread will be slowly lost during the refrigeration or freezing process, affecting the taste. Each steamed bun is packed and wrapped, which can also avoid cross-infection with other substances in the refrigerator.
In addition, it should be noted that it is recommended to eat refrigerated steamed bread as soon as possible within 3-4 days, and frozen steamed bread is recommended to be eaten within half a month. Frozen steamed buns should be fully heated before eating, so as to reduce possible food safety risks. In addition, if you are freezing steamed buns with packaging purchased from outside, it is recommended that you do not break the packaging when frozen, so that it is easier to preserve.
Q: Can I continue to eat the place where the steamed bun has been removed?
Not recommended for consumption. Many people are thrifty and see that only a small part of the food is moldy, so they will cut off the hairy place and continue to eat, but it is not recommended to eat the steamed bread that has become moldy. Although the moldy part is removed, the toxin may spread to other parts of the steamed bread, and if you continue to eat the leftovers, it may affect your health.