Can frozen steamed bread be eaten after more than two days? The scientific truth behind the fact that aflatoxin is nearly 70 times greater than arsenic

Recently, a short video claiming that "Zhejiang University found that overnight steamed bread can breed aflatoxin" has attracted widespread attention. But is this really the case?

The steamed buns stored in the refrigerator do not have the conditions for aflatoxin to grow rapidly.

Aspergillus flavus is a common mold that grows easily in a warm and humid environment . According to the experimental results of Professor Peng Jian's team at China Agricultural University, under the condition of 60% relative humidity, the minimum growth temperature of Aspergillus flavus in wheat is 6.5°C, the maximum growth temperature is 52.7°C, and the optimum growth temperature is 31.4°C. The humidity in household refrigerators is generally 40% to 60%, the temperature in the refrigerator is generally 0°C to 4°C, and the temperature in the freezer is generally around -18°C. Such a low temperature environment effectively inhibits the growth of most microorganisms, including Aspergillus flavus. Therefore, the steamed buns placed in the refrigerator do not have the conditions for the rapid growth of Aspergillus flavus.

Aflatoxin itself is not toxic, but the aflatoxin it produces is toxic.

Aspergillus flavus is a fungus belonging to the genus Aspergillus, which is widely found in the natural environment, especially in soil, plant materials and other organic matter. It is a multicellular fungus that can form hyphae and spores visible to the naked eye. A. flavus can produce different types of spores, such as conidia and blastospores, under different environmental conditions. A. flavus itself is not directly toxic, but some strains of A. flavus can produce toxic metabolites, namely aflatoxins.

Aflatoxins are a class of secondary metabolites produced by Aspergillus flavus and Aspergillus parasiticus. Its structure contains an oxygen heterocycle and a coumarin ring, which makes them chemically very stable and not easily degraded. In the environment, they can exist for a long time and accumulate through the food chain. The main types of aflatoxins include AFB1, AFB2, AFG1, AFG2, M1 and M2, among which AFB1 is the most common and most toxic one. These toxins are mainly found in food crops in tropical and subtropical regions, such as corn and peanuts. For example, 15% of peanut samples sampled in some African countries were contaminated with aflatoxins, with a content as high as 1000~10000 μg/kg. In the high temperature and high humidity grain and oil areas in southern my country, the detection rate of aflatoxins is also very high.

Aflatoxin is nearly 70 times more toxic than arsenic

As early as 1993, aflatoxin was classified as a naturally occurring carcinogen by the World Health Organization (WHO) Cancer Research Institute. It is a highly toxic substance. The health effects of aflatoxin on the human body are mainly manifested as liver damage. Long-term intake of low doses of aflatoxin may lead to hepatocellular carcinoma. In addition, aflatoxin is also associated with growth and development disorders in children, damage to the immune system, and genetic mutations. At the same time, according to a scientific study by the Shanghai Administration of Traditional Chinese Medicine in July 2019, the toxicity of aflatoxin is 68 times that of arsenic. Ingestion of 1 mg may cause cancer, and intake of 20 mg will be fatal . It is the most toxic mold known. If ingested in large quantities, acute poisoning will occur, and even a small amount of consumption will cause chronic poisoning.

How to deal with food contaminated with aflatoxin?

Steamed bread is rich in nutrition and has a high water content. If it is not stored properly, it is easy to be infected by microorganisms and cause quality deterioration. The bacterial plaque of steamed bread stored at room temperature mainly comes from the surface. The infection time of the surface and the inner core differs by 8 to 12 days. Although there is a significant difference, for safety reasons, it is not recommended to eat steamed bread with bacterial plaque on the surface.

Other foods contaminated with aflatoxin must also be handled strictly. They should be discarded in special trash cans, and the lids should be tightly closed to prevent the toxins from spreading to the surrounding environment. Surfaces that have come into contact with contaminated food should be thoroughly cleaned and disinfected, such as storage containers, knives, and cutting boards. In order to prevent food from being contaminated by aflatoxin again, appropriate storage measures should be taken, including keeping the storage environment dry and clean, and strictly controlling the temperature. Through these preventive measures, we can effectively protect food from aflatoxin and ensure food safety.