In the most general and literal meaning of the term, the mycotoxins are toxic substances produced by fungi, and the first thought related to fungi inevitably evokes the image of Amanita muscaria, the red muscimol mushroom, white-spotted, the most recognizable by children!
It is necessary, however, to open the horizon: it is not only the fungi that produce mycotoxins, because among the fungal species harmful to humans we also find mould. Their nature is parasitic, as all the organisms of the kingdom of living: they infest an host (plant or animal) absorbing part of its nourishment and, through their metabolism, produce some waste substances, the so-called secondary metabolites, which are toxic to many organisms.
Which are the main types of mycotoxins and what is their toxic potential?
Among the most interesting mycotoxins in cereal cultivation, there are three categories:
- Aflatoxins (produced by Aspergillus moulds): they are one of the best known groups of mycotoxins for health food, as they infect both cereals and nuts (hazelnuts, peanuts, …). If ingested by livestock, through the feeds, they can remain in the alimentary products that come from the breeding, like dairy products and meat, becoming therefore dangerous also to humans. Aflatoxins B1, B2, G1 and G2 have been recognized as carcinogens since 1994;
- Ochratoxins (produced by Penicillium fungi): one of the most dangerous substances in this group is ochratoxin A, a very stable compound, resistant to the standard roasting temperatures of grains and nuts and it’s insoluble in water. It can cause severe damage to the kidneys and liver if it is absorbed by the intestine;
- Fusarium -toxins (produced by Fusarium): infections by these fungi occur mainly through the skin, and the toxins that they produce can give rise to various pathologies, from keratitis to peritonitis. However, no significant complications arise unless the infection is already immunocompromised. The most common fusarium-toxins are fumosine (suspected as carcinogenic) and zearalenone, which alters the production of estrogen and, in the most extreme cases, causes abortion.
The Italian and European legislation: limit thresholds not to be exceeded to prevent food contamination
The presence of a species included in these categories is determined above all by the thermo-hygrometric conditions (temperature and humidity) of the conservation of the cereal. The threshold limits for the quality of the product during analytical surveys are established by regulation 1881/2006 issued by the European Commission (EC), for mycotoxins and for inorganic contaminants.
Considering Ocatoxin A, the Circular dated 18/02/2010 issued by the Ministry of Health set the limit for 8 μg / kg of fresh product for cereals, updating the previous limit, set at 5 μg / kg.
The regulation for aflatoxin is even more severe (4μg / kg of unprocessed cereals). Considering the the hot climate and the prolonged storage times contribute to the development of mould, the risks of contamination increase when are used foreign imported cereals.
How to avoid the contamination in a milling plant?
In the milling plant, the precautions to be taken start from the arrival of the cereal. The silos have to be loaded quickly and it’ recommended the addition of propionic acid (a mould inhibitor, used as a preservative in the food industry) at a low concentration in the upper portion of the grain heap, the next in contact with air.
The addition of products that counteract parasites must not however be a substitute of the temperature and humidity monitoring of cereals: a temperature of 26-28 ° C favours the appearance of microorganisms. Also keeping trucks with raw material in long waits under the sun, can be a source of damage of the product quality. The European guide to good hygiene practices in grain storage is very clear on these points.
For greater safety, periodic analysis and sampling of cereals must be provided during storage. Sampling must be carried out in accordance with CE 152/2009 and ISO standards, taking into account the characteristics of the contaminant.
The mycotoxins are known to have an heterogeneous distribution of wheat or maize loads, since the grains tend to mix in the pile. Therefore, taking a single sample is not sufficient as a quality indicator, but several are needed. Moreover these contaminants are present in very low concentrations, and it is necessary to use instruments endowed of strong sensibility to trace them.
The standard test expects an extraction of the substance, its purification to avoid interferences from other molecules and, finally, a quantification. The last phase uses immunoenzymatic tests, which include the introduction of an antibody capable of binding the mycotoxin and then checking the quantity of substance that took part in the reaction, and therefore the actual content of the sample.
If carrying out the necessary tests to verify the presence of mycotoxins in the wheat is useful for understanding the state of the raw material and ascertaining its maximum quality, working in a preliminary manner on the level of storage silos, makes it possible to act at the start to avoid the problem of contamination!