You’ve bought a fancy artisan wholemeal bread made from only natural ingredients, no preservatives it proudly states. It was expensive so you only eat half of the bread, saving the rest for another day. It was wonderful. Two days later when you intend to eat the other half it is all mouldy.
In poorer circumstances there is no option but eat what is on offer. But in an affluent society we have the option to throw it out, even if it hurts as it was so nice. Or you could attempt to rescue the unaffected part.
What to do?
Let’s look at the facts
Moulds belong to a large and taxonomically diverse range of fungal species that characteristically grow hyphae. The hyphae are generally transparent, so they appear like very fine, fluffy white threads over the surface, especially on food. We have tamed some moulds to become beneficial, others cause food spoilage, and yet others are seriously harmful to human health.
On the beneficial side, the most well-known mould product is penicillin produced by the Penicillium mould and used as an antibiotic to kill bacteria. Moulds are also essential components in the manufacturing of several food products, such as some cheeses, sausages and soy sauce.
On the harmful side, several moulds produce compounds toxic to animals and humans called mycotoxins. The worldwide contamination of food and feed with mycotoxins is a significant problem. According to the Food and Agriculture Organisation of the United Nation 25% of the world’s crop harvests are contaminated with mycotoxins. There are currently more than 400 known mycotoxins.
Where to find mycotoxins?
Mycotoxins can occur in a wide range of different foodstuffs. These include cereal-based products – such as bread, breakfast cereals, pasta, pastries, biscuits and snacks – groundnuts (peanuts), tree nuts, oilseeds, dried fruits, spices, coffee, wine, apple juice and milk. Mycotoxins are typically highly resistant to temperature and processing, so destruction during conventional food production does not occur.
The mycotoxins of most concern from a food safety perspective include the aflatoxins (B1, B2, G1, G2 and M1), ochratoxin A, patulin and toxins produced by Fusarium moulds, including fumonisins (B1, B2 and B3), trichothecenes (mainly nivalenol, deoxynivalenol, T-2 and HT-2 toxin) and zearalenone.
A threat to health
Mycotoxins can cause a variety of acute and chronic adverse health effects.
- Aflatoxins, and in particular aflatoxin B1, are genotoxic and carcinogenic, and can cause liver cancer in humans.
- Ochratoxin A causes a number of toxic effects in animal species. The most sensitive and notable effect is kidney damage. It may also have effects on foetal development and on the immune system.
- Patulin has been shown to have various toxic effects and can harm the immune system and gastrointestinal tract.
- Fumonisins have been related to oesophageal cancer in humans, and to liver and kidney toxicity in animals.
- Trichothecenes can be acutely toxic to humans, causing sickness and diarrhoea, but at much higher levels than those typically present in food. Reported chronic effects in animals include suppression of the immune system.
- Zearalenone is oestrogenic and has been shown to exhibit hormonal effects, such as infertility, particularly in pigs.
What to do with the mouldy food?
All of us have observed mould growth on food – be it on the piece of bread above or on a plum left sitting on the kitchen counter for an extended period of time. But you have no idea if this is a mycotoxin-producing mould harmful to health or just an annoyance spoiling the food.
There is a simple rule of thumb. For firm foods cut off the piece affected by the mould and eat the rest, while mouldy soft foods should be discarded.
Hard cheeses are good examples of firm foods that can be rescued. Moulds need moisture to grow and in dry cheeses like cheddar and parmesan there is not enough moisture for the mould to penetrate beyond the surface. Thus it is fine to remove a two centimeter piece of the cheese around the mould avoiding to cut into the mould.
Similarly, firm fruits and vegetables (such as cabbage, bell peppers and carrots) are fine to eat after removal of the mould.
And by all means remember that for some foods, like certain soft cheeses and processed meats, mould growth is part of the manufacturing process and they are perfectly fine.
On the other hand, mould on the surface of fluid foods such as yoghurt usually means that its mass of thread-like filaments have penetrated the item. Better discard the lot.
But how about our artisan bread, it is fairly dry but not really hard? This case is a little trickier. It might be sufficient to remove a solitary mould and eat the rest of the bread. However, with more extended mould growth the risk is higher. It might pay off to throw away the lot.
A final word of warning
It is generally acknowledged that aflatoxins are genotoxic carcinogens. As a matter of fact they are amongst the most potent mutagenic and carcinogenic substances known.
A number of epidemiological studies have shown clear associations between aflatoxin exposure and incidence of liver cancer in areas with high prevalence of chronic hepatitis B, which is itself a risk factor for liver cancer.
Unfortunately, global warming will exacerbate the situation as mycotoxins occur more frequently in hot and humid climates favouring the growth of moulds.
The future might be bleak unless action is taken now to curb greenhouse gas emissions.