Mycotoxins: prevalence and control An interview with Dr Perez Vendrell

• The rise in organic production of cereals

Every year more and more hectares of land are destined to the biological production of cereals, which comports a reduction in the utilization of pesticides, particularly fungicides. To avoid the proliferation of fungi, farmers put in practice systems such as crop rotation and reduction of the amount of nitrogen used as fertilizer.

• The boom in production of biofuels

In the production of bioethanol, the conditions in which cereals such as maize and wheat are processed may increase the change of fungal contamination of by-products.

• Climate change

Microenvironmental factors, such as temperature and relative humidity, influence the life cycle of fungi and their ability to produce mycotoxins. The progressive rise in temperatures, as well as reduction in water availability, may condition the efficacy of the pre-harvest application of fungicides and pesticides. This may result in an increment in the number of pathogens and mycotoxins throughout the food chain.

Increasing temperatures can also affect the geographic distribution and life cycle of insects that promote fungal infections in crops. This results in food borne diseases of warmer latitudes appearing in new environments.

Scientists have also observed that, due to climate change, some species of fungi are being displaced by more virulent, aggressive ones. For example, the FAO, in its 2008 report “Climate change and its implications in food security”, described that Fusarium culmorum is being replaced buy F. graminearum, of grater virulence. In countries with mild climate (e.g. Southern Europe), raises in temperature will favour the development of Aspergillus spp.  and the production of aflatoxin B.

What mould species (and their mycotoxins) have higher prevalence on animal feeds?

Although more than 300 types of mycotoxins have been identified, only thirty of them have toxic properties of concern. These mycotoxins are natural contaminants found in vegetal products, such as cereals (maize, wheat, barley, rice, and their by-products) and fruits (pistachios, nuts, and almonds). Likewise, mycotoxins and their metabolites can be found in animal products, e.g. aflatoxin M1, present in milk of cows eating contaminated feed.

The mycotoxins most commonly found in animal feed ingredients are aflatoxins (mainly B1), ochratoxin A, zearalenone, deoxynivalenol (DON), T-2, fumonisines (mainly B1 and B2). The first two are produced by species of the genera Aspergillus and Penicillium and the rest, by the genus Fusarium.

Fungi can be differentiated into two groups according to the moment when they produce their toxins. The first group produce toxins while the plants are in the field (e.g. zearalenone), whilst the second group produce mycotoxins after harvest, mainly during storage (e.g. ochratoxin A).

Worldwide, the areas with higher prevalence of mycotoxin contamination are North America and Southern Europe. Globally, DON is the most common mycotoxin, with 66 % prevalence in raw materials for animal feed, and a mean level of contamination is 1394 ppb (according to tests conducted in 2014).

Other mycotoxins found in more than half of the samples analysed in 2012, at levels above recommendations, were fumonisines (56 % of the analysed samples, with an average concentration of 1594 ppb) and zearalenone (54 % of the analysed samples, with an average concentration of 221 ppb) (Biomin Survey Report 2014).

Regarding the incidence and high prevalence of mycotoxins…

What are the most important factors determining the sustained prevalence of the problem?

The formation of mycotoxins depends on many factors such as humidity, temperature, presence of oxygen, time for the fungus to develop, integrity of grains, etc. Procedures for drying grains, as well as storage, also contribute to contamination with mycotoxins. Controlling those factors to prevent contamination is many times difficult. For example, to prevent fungal growth, stored grains should not have a water activity above 0.65, and the temperature of the mass of grains inside the silos should not rise above 20°C. Many times, these requirements are not fulfilled, situation aggravated when the aeration is deficient or there is an excess of impurities. These are just some of the reasons determining their high prevalence.

You have been a member of EFSA (European Food Safety Authority). From the point of view of food safety…

What are the necessary controls to reduce mycotoxin prevalence?

Firstly, it is necessary to minimise the presence of toxigenic fungi by applying Good Agricultural Practices (GAP) during plant development, as well as by controlling temperature and humidity during grain storage.

Once harvested, grains could be cleaned (by dust aspiration, washing with sodium carbonate, separation of defective grains, etc.). The decontaminating efficacy of these techniques is relative. Mycotoxins are highly thermoresistant, therefore thermal treatments are generally inefficient to decontaminate grains.

Do you consider that the maximum levels of toxocity established for some mycotoxins are adequate?

When establishing máximum levels of mycotoxins in raw material and animal feeds, acute toxicity and chronic toxicity (produced by low levels of mycotoxins) are considered. Recently, however, other aspects are also being considered, such as the effect of combination of several mycotoxins, as well as the toxicity of modified mycotoxins and their metabolites. By means of more sensitive tests, the effect of mycotoxins is evaluated not only on target tissues, but also on the immune system, on the digestive tract, and on normal growth, even in animals not yet showing signs of toxicity. All this suggests that, in the future, accepted maximum levels of toxicity may be lowered.

Considering that mycotoxins evolve, the EFSA has already evaluated group of “modified mycotoxins”…

What does the term “modified mycotoxins” entail?

The EFSA applies the term “modified mycotoxins” to the group comprising masked mycotoxins, mycotoxin “bound” to other molecules (usually polar), as well as mycotoxin metabolites. In a broader sense, modified mycotoxins are those in which the chemical structure has been altered. Until not long ago, this group of mycotoxins appeared in some analyses of original mycotoxins, and were called “masked”. Modified mycotoxins could be hydrolysed, biotransformed, and absorbed in the gastrointestinal tract, similarly to the original mycotoxins.

Although different from the original molecules, modified mycotoxins should also be considered when measuring the total levels of contamination. Their contribution is difficult to determine precisely, since this will depend on the type of mycotoxin and its modified form, as well as of the product used for detoxification.

Ruminants are more resistent to mycotoxins compared to other species. However, it is necessary to control the transference of mycotoxins to the milk, especially aflatoxins and their metabolite AFM1.

Some analytical procedures already help to detect the presence of different mycotoxins at very low levels. Although they can be used by the feed industry to control raw materials and feed (some of them even for routine controls) their cost is still very high. Currently, sensors are being developed to detect mycotoxins in a more rapid and economical way.

Regarding mycotoxin control, there are two basic strategies: binding/elimination of toxins and detoxification…

What is your opinion on such control strategies and what are the advantages of each one of them?

Both strategies are necessary because not all mycotoxins respond in the same way. Binding agents have efficacy mainly against aflatoxins, ochratoxin A and T-2, but not against most trichothecenes. For the latter group, the most effective detoxifying strategy is to degrade the toxins to non-toxic metabolites by means of bio-transforming agents such as certain bacteria, fungi, yeasts or enzymes. In other words, a combination of both types of strategies is recommended.

The development of new treatments to fight against mycotoxins is of highest priority…

Could you explain the priorities established in current research projects to fight against mycotoxins?

Mycotoxins are compounds of heterogeneous physical and chemical properties. Therefore, detoxification methods effective against some types of mycotoxins are not effective against others. For example, detoxifying products based on the adsorption/binding principle are not adequate for trichothecenes.

Research projects encompass diverse fields: Development of new methods of detection and analysis of mycotoxins, study of mycotoxin metabolites and their toxicity, investigating possible synergisms between different mycotoxins, development of mechanisms of detoxification. In the case of mycotoxins with low adsorption, for example, researchers are trying to biotransform them with specific enzymes that break down their toxic structure.

More concretely, what are the projects running at your research center?

I our research centre, we perform in vivo studies on birds and piglets to evaluate the efficacy of detoxifying products of certain mycotoxins.  We evaluate productive parameters of the animals, collect blood and faeces samples, weight organs, and study the integrity of the gastrointestinal tract and of the immune system. In the collected samples we analyse the presence of mycotoxins under study. This is done following the experimental conditions specified by EFSA.

This interview was originally published in 2015 on nutriNews Spanish edition, with the title Entrevista con Anna M^ªPérez-Vendrell (IRTA)