We have a lot of walnuts, but not immediately dried properly. On some I see a bit of mold, on others not. Are the nuts that look good and taste good good? Or could it still contain mold that is carcinogenic, and how much of it is harmful to eat?
Answer
Dear Ms,
nuts in general are sensitive products to mold. This is because they are normally a little too dry to mold, but if they are a little too moist, mold can grow.
Most molds are harmless; just think of blue cheese! we eat them ourselves.
However, some fungi are toxic; this is because the fungus produces toxins that we learned to call mycotoxins, or fungal toxins.
A lot of these fungal toxins are already known; one is already a bit more toxic than the other, but there are a few very unpleasant cases. A very dangerous one is actually this one that was first discovered in the 1960’s in England. These are so-called aflatoxins, or toxins from the fungus Aspergillus flavus (hence the name a-flatoxins). These substances are without discussion carcinogenic to humans, more specifically it is a primary liver carcinogen. So it really is a dangerous stuff. The legal limits are therefore particularly low: 1 µg/kg or 1 mg sugar in 1 cubic meter of water, so to speak!
Checks are made, but of course if you have nuts at home, they are not checked (not all nuts in the trade are checked of course). So if you have a nut that is mouldy, just throw it away – after all, you don’t know whether there is the ‘good’ or a ‘bad’ fungus.
Final remark – unfortunately I am not going to reassure you: the absence of a fungus does not necessarily mean that there may be fungal toxins in the nut: after all, the fungus may already have ‘perished’, so that it is no longer visible; however, the toxins are very stable and remain. So don’t eat half a kilo of nuts every day! But I have to admit that they are very tasty and I can hardly stay away from them!!
Regards
Bruno De Meulenaer
Answered by
Prof. Dr. ir. Bruno De Meulenaer
Food Science Food Chemistry
http://www.ugent.be
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