| FOOD SAFETY - The war on mycotoxins
Man has long benefited from the nutritional properties of certain microscopic fungi, such as ferments and yeasts used in making cheese, beer, bread, vinegar and yoghurt. But some moulds of fungal origin are potent poisons, especially the mycotoxin family which has been the subject of increased attention over the past 15 years. European research by the Mycotoxin Prevention Cluster project is currently making a very close study of ways of protecting consumers against these threats which pose a very real problem to food safety and public health.
Mycotoxins are dangerous, invasive and perverse. The carcinogenic effects of many of them are proven, while some varieties could also have damaging cytotoxic (cell destruction), teratogenic (triggering of hereditary deformations) or immunity effects.
|As perverse as they are diverse, mycotoxins are particularly dangerous due to their action at sometimes very low concentrations and their impressive stability. These harmful molecules resist high temperatures and certain industrial processes.|
Belonging to different families,(1) mycotoxins can be present in a wide range of food products. Cereals are their favoured targets – rendered all the more vulnerable as they are stored in large quantities – but they are also found in fruits and vegetables. From time to time they appear in potatoes, pears, tomatoes, carrots, grapes, nuts, peanuts and even coffee and cocoa. Some studies estimate that 25% of the world’s agricultural production could be contaminated, although obviously in varying concentrations.
They are all the more dangerous as they can sometimes be active at incredibly low concentrations. ‘This is on an altogether different scale to the classic and demonstrated toxicity arising from the use of certain industrial solvents by the food industry, such as carbon tetrachloride, for example,’ explains Professor Naresh Magan, of Cranfield University (UK), coordinator of the Mycotoxin Prevention Cluster project. ‘We know that this latter product causes tumours in 50% of rats exposed to a dose of 0.2 grams per kilo per day. However, a well-known mycotoxin, such as aflatoxin B1, is 33 million times more dangerous than this dangerous solvent – its threshold is 0.000001 grams per kilo per day.’
The problem is rendered even more serious by the impressive stability shown by many of these molecules. They resist high temperatures and certain industrial processes. Cooking provides no protection and the poison can remain present even after the fungus itself is destroyed. The absence of mould, therefore, is no guarantee of food quality.
So what can be done? Checks at the product distribution stage are undoubtedly a vital safeguard, but ‘intervening in this way to prevent poisonings by withdrawing contaminated food from the shelves is a far from satisfactory emergency solution’, stresses Naresh Magan. ‘Real progress must come from upstream preventive action, which is the reason for our European research. Our strategy involved identifying the critical points in the food chain and defining the procedures to avoid these situations – from the pre-harvest stage right up to marketing and including storage, and all the other stages along the way’. Known as HACCP (Hazard Analysis by Critical Control Points), this approach is now traditional practice at the industrial processing stage of food production, although less common upstream.
Ten species of fungus were the subject of particularly close study. Researchers looked at the most favourable conditions for mould proliferation and the emission of toxins, especially in terms of temperature, humidity, gaseous composition and chemical products present (particularly fungicides). They discovered some surprising phenomena. Low doses of fungicides, for example, sometimes have the effect of causing stress in the fungus which, paradoxically, stimulates toxin production.
|Comparative tests on resistance to infection by Fusarium graminearum on separated batches of wheat plants.|
Above:cross-section of a wheat inflorescence, the right area showing colonisation by mycelian filaments of Fusarium culmorum.
© C.Waalwijk/GHJ. Kema
A mathematical model was compiled to calculate the acceptable storage time depending on temperature and hygrometry. This showed that, for cereals, anything above 20% humidity fails to guarantee food safety, even for a very short time. It is therefore essential to dry the grains. This research will make it possible to develop warning systems which take into account often critical meteorological conditions. There are, in fact, “mycotoxin years”, while others can be comparatively mycotoxin-free. It should therefore be possible to alert professionals to the potential danger and recommend the procedures to follow depending on the risk factors.
Advice on silo design and maintenance is already being circulated in the wake of this research. Ventilation systems which prevent condensation can be very useful, for example, in tackling the crucial issue of humidity. Shortcomings in terms of watertightness are also frequently observed and professionals are advised to inspect their plant and equipment prior to harvest. As it is generally at the top of the silos that contamination first takes hold, it is there that the strictest checks must be carried out. Measuring the silo temperature, using carefully distributed thermometers, also helps reduce risks.
One fungus can drive out another
Other possible avenues for prevention are also being explored. We know, for example, that some antioxidants, especially essential oils, are quite effective in preventing the formation of mycotoxins. The feasibility of using them on a large scale is currently being investigated, considering both the financial and the technical aspects.
|Inadequate storage conditions in silos can have very serious consequences for human health, even proving fatal sometimes. Last April in Kenya, maize contaminated with aflatoxins caused 80 deaths, with a further 180 patients hospitalised.|
‘Biological combat’ is another option. As not all varieties of fungus produce toxins, it is conceivable to favour the presence of a non-toxic variety which would prevent a dangerous rival from becoming established. Among members of the genus Fusarium, for example, which grows on all cereals, researchers have identified non-toxic varieties whose presence reduces the toxin quantity by between 60 and 70%. Chemical fungicides are no more effective than this. At present, however, the legislation presents an obstacle to the marketing of these non-toxic strains as the approval procedure is the same as for synthesised products and therefore very costly. Nevertheless, one of the SMEs involved in the project is now looking at ways of marketing this solution.
Another important part of this puzzle concerns the effects of the various industrial processes on contamination. Although cooking is not enough to eliminate toxicity, the succession of processes does reduce the concentrations present. Scientists studied this phenomenon in ochratoxins, which are particularly noxious elements with a special affinity for coffee and cereals. They estimated that the grains lost between 2% and 3% of their contamination during washing, between 3% and 44% during defatting, up to 60% during grinding and between 5% and 10% during boiling. Similarly, various stages in the beer production process reduce the toxicity of the barley by around 20%. This information is very valuable to the legislator as the tolerable contamination levels vary depending on whether it is a product intended for direct consumption or one which will be subject to extensive processing.
This body of data will be all the more useful as the Union is set to introduce new regulations for mycotoxins. Legal limits already exist for the principal mycotoxins (ochratoxins, aflatoxins), but the list will soon be extended.
(1) Mainly aflaxtoxins, ochratoxins, trichothecens and patulin.