What are mycotoxins?
Among the metabolic products created by molds, the chemical substances which express harmful effects in humans and animals are collectively referred to as mycotoxins.
There are currently over 300 varieties of reported mycotoxins confirmed to exist. The event which served as the impetus for the growth of mold research in Japan was the occurrence of the so-called “yellow rice” incidents. Molds were found in rice imported from Southeast Asia, Egypt, and Spain after the Second World War which produced a strong mycotoxin which caused liver damage.
In addition, in the UK in 1960, an incident in which 100 thousand turkeys died in the span of a month due to liver failure was found to have been caused by feed which contained mycotoxins.
Conventionally in Japan, food and molds had largely only been looked at from the perspective of fermentation and spoilage, but incidents and accidents such as these led mycotoxins coming to be viewed as a new problem in these areas.
How do mycotoxins spread?
Aspergillus flavus is a mold which produces the well-known carcinogenic mycotoxin called aflatoxin. There is virtually no possibility of Aspergillus flavus contamination in agricultural products produced in Japan. This mold has, however, been confirmed to exist widely throughout the tropics and subtropics. Consequently, it is possible for agricultural products imported from countries in these areas to be contaminated with this mold.
Conversely, Fusarium contamination is a problem in regions from the temperate zone to the frigid zone.
Fusarium can reproduce explosively on crops such as barley when weather conditions are right. In turn, contaminated crops can cause problems such as miscarriage in pigs when fed to them as fodder.
What regulations are there concerning mycotoxins?
In Japan, a limit of 10 μg/kg for total aflatoxin has applied to all foods since October 2011.
Can mycotoxins be eliminated through cooking?
１ Mycotoxins are resistant to heat
Mycotoxins cannot be completely destroyed under normal cooking temperatures (100 to 210° C) and times (under 60 minutes).
２ Can mycotoxins be destroyed via home cooking methods?
If mycotoxins in food could be reduced through standard cooking methods such as boiling, sautéing, and rice cooking, there would be no problem. For example, however, it has been found that after boiling 50 to 80% of mycotoxins remain in food, with around 10 to 15% found in the water used for boiling. As can be seen from this example, boiling destroys only a small amount of potential mycotoxins in food.
Frying in oil and standard methods of rice cooking also similarly eliminate almost no mycotoxins.
|Food||Cooking method||Mycotoxins||Mycotoxin amount (ppb)|
|Before cooking||After cooking (%)|
|Job’s tears||Rice cooking||Zearalenone||840||740(88.1)|
|Rolled barley||Rice cooking||Deoxynivalenol||264||235(89.0)|
Mycotoxin survival rate (%) after cooking shown in parentheses
Can mycotoxins be removed via industrial food production processes?
Industrial food production processes include steps such as heating and washing. As these processes do not differ significantly from cooking conditions in the home, similar to the methods discussed above, they do little to reduce potential mycotoxin content.
Then what about the effects of food additives?
Let us look at an example using cooking oil made from corn contaminated with mycotoxins. The cooking oil production process includes steps such as deoxidation, decolorization, and deodorization to prevent foreign matter from being included in the product. Alkaline chemicals are used in the deoxidation process, and these would destroy the majority of the mycotoxins in our theoretical cooking oil made from contaminated corn. Any remaining mycotoxins would further be destroyed in later refining processes, resulting in a product completely free from mycotoxins.
In the case of nuts and grains contaminated with mycotoxins, as mycotoxins are resistant to heat, they would not be destroyed as part of normal product processing. However, it is known that plants which are filled with holes or which are of an irregular color are often contaminated, leaving no choice but to pre-sort which plants to use for a product in order to eliminate any potential mycotoxins. Sorting methods can be broadly categorized into methods which use machines to eliminate unwanted plants and methods in which people eliminate unwanted plants (hand-picking).
As shown in the table below, hand-picking shows a dramatic difference between the amount of mycotoxins in plants determined to be inferior and those which meet product standards. Hand-picking, of course, depends on the skill of the people conducting the sorting, but to date it has been confirmed that hand-picking is more effective than sorting conducted by machines.
When eating peanuts and other nuts at home, it is safest to avoid eating those which are moldy, which have holes in them, which taste bitter when eaten, or which are not mature.
Efficacy of peanut sorting
|Nuts with mold||Nuts with holes||Nuts with abnormal color||Product-suitable nuts|
|No. nuts sorted||100||100||80||500|
|No. nuts contaminated w/ mold||22||12||2||0|
|Mold intermix rate (%)||22||12||2.5||0|