Counteraction and Preventive Methods
Prevention can only reduce, not eliminate, the risk of mycotoxin contamination. This is due to the impact of climatic conditions on the presence of mycotoxins, which cannot be influenced by human beings.1 However, there are some ways to maximize plant performance and reduce stress to substantially decrease mycotoxin contamination. These include good agricultural practice (GAP), which is the precondition to minimizing the contamination of grains with mycotoxins; implementation of good manufacturing practice (GMP) during the handling, storage, processing and distribution of cereals.1,2 Solutions to reduce and minimize mycotoxin contamination are divided into pre-, during and post-harvest (Table 1).
|Pre-harvest control||Harvest and post-harvest control|
|Breeding||Appropriate harvest time|
|Sowing time||Appropriate harvest equipment|
|Irrigation||Humidity level before and during storage|
|Proper crop rotation||Temperature during storage|
|Tillage||Appropriate harvest time|
|Adequate fertilization||Appropriate harvest equipment|
|Weed control||Use of fungicides and mycotoxin deactivating products|
BreedingThe breeding of resistant or less susceptible grains is important to prevent fungal growth and mycotoxin production and can be considered as the best solution for Fusarium control.1,2
Sowing timeThe sowing time has an impact on the flowering stage of the plant, which means that the earlier the planting date, the earlier the flowering stage of the grain is reached. Mycotoxin contamination is highest when the crop reaches its flowering stage during the time of spore release.4 This correlation between planting date and the achievement of different production stages means that the planting date and also the ripening of the variety can significantly influence fungal growth and mycotoxin production. For instance in maize, earlier planting dates often result in lower contamination levels, therefore poor weather conditions can pose a higher risk.4 Regarding wheat and barley, winter varieties develop and mature earlier than spring varieties, hence the winter varieties have a reduced risk of Fusarium infection.2
IrrigationIrrigation can lead to reduced plant stress in some growing stages, but should be avoided during flowering and ripening of the crops, especially in wheat, barley and rye, because excessive precipitation, particularly during flowering, favors dissemination and infection by Fusarium sp.1
Proper crop rotation
Cropping systems where maize is rotated with wheat or wheat is grown each year in the same field, appear to increase the disease epidemic. Therefore, without crop rotation there is a greater risk of mycotoxin infection.
Multi-field crop rotation with rape, sugar beet, sunflower or soybeans reduces the appearance of mycotoxin infection.1,2 For example, Schaafsma et al. (2001) observed that planting crops other than wheat two years before growing wheat in a particular field significantly decreased the level of Deoxyniyalenol (DON) in the year the wheat was grown.5
The mechanical, insect or bird damage of grains provides a good opportunity for fungal infection and damage, thus their prevention is of major importance. In the first year plants get infected with fungal spores, and these can colonize other plants and also settle on the soil. After harvest the maize stubble remains in the soil and can be colonized by fungi. If maize is grown in the same field the following year, it can be further contaminated.2
TillageProper soil cultivation and management of residues on the field are imperative to reduce the risk of mycotoxin contamination. For example, ploughing (10-30 cm into the soil) is more effective against mycotoxin contamination compared to minimum tillage (10-20 cm into the soil) and no tillage (seeds drilled into previous crops). Post-harvest ploughing can reduce the growth of F. graminearum, which causes Gibberella ear rot and DON contamination, with maize being very susceptible to this Fusarium species. In addition, the removal, burning or burial of crop residues can reduce the occurrence of Fusarium species in the following crops.1,2
Adequate fertilizationThere is evidence that the use of fertilizers can affect the contamination level of Fusarium sp. of crops by modifying the residues, influencing the plant growth and changing the soil structure along with its microbial activity.1
Weed controlWeeds can contain a broad range of Fusarium species. Any crops which are highly weedy, for example wheat, will have a higher level of contamination.6
Harvest and post-harvest control
Appropriate harvest timeHarvesting at the appropriate time is essential for reducing the risk of a mycotoxin contamination. In general, early harvest leads to lower concentrations of mycotoxins. Additionally, special attention should be paid to careful harvesting procedures and proper drying of the grain.1,2
Appropriate harvest equipmentAppropriate harvest equipment should be used to avoid damage to the grain kernel, as damaged kernels could be predisposed to infection during storage. Additionally, the equipment should be free from residual grain from the previous harvest to avoid cross contamination. Fusarium spores insoil are a ubiquitous issue, meaning it is important to avoid contact between the soil and the harvesting machine in order to reduce the risk of mycotoxin contamination of healthy grain.1,2
Humidity level before and during storageBefore storage the grain damaged kernels should be removed to reduce the infection rate.. Grains should only be stored at 15% humidity or lower so high moisture parts should be removed prior to storage to reduce the risk of contamination.1,7 Water in the grain creates an ideal growth environment for fungi. The water activity (aw) of the grain must be below 0.65 and the humidity or total water content level must be under 140 g/kg to avoid fungal growth. However, there are big differences between different fungi. For instance, Aspergillus sp. can grow at very low water levels, while Fusarium sp. needs higher moisture contents. Atmospheric humidity can play an important role, as it varies a lot between morning dew and afternoon sunshine. The harvesting time of day also plays an important role in the development of Fusarium sp. in grains post-harvest. Delayed harvesting in late autumn can be very wet, which favors mold production. To prevent further fungal growth in high humidity level grain, it is essential to dry the grain before storage. Unfortunately, due to their chemical stability, a reduction of trichothecenes, fumonisins or zearalenone will not arise in the course of the drying process.1,2,8
Temperature during storageBesides humidity, the temperature during storage is also important for the control of fungal growth. If fungal growth takes place, the temperature inside the contaminated spot is higher than in the rest of the silo. With the distribution of temperature recorders at different heights in the silo, any microbial activity can be detected. To combat fungal growth, combined cooling and drying operations together with ventilation systems are necessary to avoid further contamination. Another way to reduce the presence of wet spots inside the silo is to rotate the grain from time to time.2
The procedures described above will only help to reduce, but not eliminate, the issue of mycotoxin contamination; hence, it is crucial to adopt valid detoxification strategies to deactivate mycotoxins directly. These are divided into four categories: physical and chemical methods, adsorption and biological methods (biotransformation).2
Physical deactivationThese methods include techniques such as:
- Optical sorting, an automated sorting method that uses cameras and lasers to analyze images and shapes of commodities, and compares them to reference samples.
- Mechanical separation, where the clean fraction of the product is physically separated from the contaminated fraction.
- Density segregation, where good versus contaminated kernels are sorted by flotation.
- Other methods include thermal treatments such as extrusion, mild pyrolysis (torrefaction), pressure-cooking; irradiation via UV beams; solvent extraction (transfer of contaminants between two separate and immiscible liquid phases). Other thermal treatments include the use inactive gasses to deactivate contaminants.2,3
Chemical deactivationThese methods use chemical agents to reduce contamination in crops. Common procedures include treatments with ozone, ammonia, use of chemicals for the control of insects and pest plants.2,3
AdsorptionThe addition of adsorbent materials (aka binders) to animal feeds is a very common method to prevent mycotoxicosis, especially aflatoxicosis. These compounds bind mycotoxins in the gastrointestinal tract, thus reducing the number of toxins going into the blood stream.9,10 Efficacious adsorption of mycotoxins depends on the polarity and shape of the mycotoxin, and on the type of bond that is formed between the toxin and the adsorbent. Because of these conditions, only a few mycotoxins can be adsorbed efficiently (e.g. aflatoxins).2,9 The adsorption efficacy of the most important mycotoxins is shown in Figure 1.
Biological methods: biotransformationThe term biotransformation stands for the chemical modifications carried out by enzymes produced by microorganisms on chemical compounds (e.g. mycotoxins). This approach is based on the deactivation of mycotoxins directly in the gastrointestinal tract and offers a very specific, irreversible and efficient way of detoxification. This strategy is particularly suitable towards less or non-adsorbable mycotoxins and it currently represents the state of the art detoxification approach.2,9,10,11,12,13
- Awad, W. A., Ghareeb, K., Böhm, J. & Zentek, J. 2010. Decontamination and detoxification strategies for the Fusarium mycotoxin deoxynivalenol in animal feed and the effectiveness of microbial biodegradation. Food Additives and Contaminants - Part A Chemistry, Analysis, Control, Exposure and Risk Assessment, 27, 510-520.
- Jouany, J. P. 2007. Methods for preventing, decontaminating and minimizing the toxicity of mycotoxins in feeds. Animal Feed Science and Technology, 137, 342-362.
- Hahn I., Krska R., and Berthiller F. 2015 Pre- and post-harvest strategies for the prevention, inactivation and detoxification of mycotoxins in food and feed.
- Munkvold, G. P. 2003. Cultural and Genetic Approaches to Managing Mycotoxins in Maize. Annual Review of Phytopathology.
- Schaafsm, A. W., Tamburic-Ilinic, L., Miller, J. D. & Hooker, D. C. 2001. Agronomic considerations for reducing deoxynivalenol in wheat grain. Canadian Journal of Plant Pathology, 23, 279-285.
- Teich, A. & Nelson, K. 1984. Survey of Fusarium head blight and possible effects of cultural practices in wheat fields in Lambton County in 1983. Canadian Plant Disease Survey, 64, 11-13.
- Miller, J. D. 2001. Factors that affect the occurrence of fumonisin. Environmental Health Perspectives, 109, 321-324.
- McMullen, M., Jones, R. & Gallenberg, D. 1997. Scab of wheat and barley: A re-emerging disease of devastating impact. Plant Disease, 81, 1340-1348.
- Schatzmayr, G., Zehner, F., Taubel, M., Schatzmayr, D., Klimitsch, A., Loibner, A. P. and Binder, E. M. (2006). Microbiologicals for deactivating mycotoxins. Mol. Nutr. Food Res. 543-551.
- Binder, E. M., Heidler, D., Schatzmayr, G., Thimm, N., Fuchs, E., Schuh, M., Krska, R., and Binder, J. (2001) Microbial detoxification of mycotoxins in animal feed. Sabino, M., Rodriguez-Amaya, D., and Corrêa, B. 10th International IUPAC Symposium on Mycotoxins and Phycotoxins. Mycotoxins and Phycotoxins in Perspective at the Turn of the Millennium , 271-277.
- Fuchs, E., Binder, E. M., Heidler, D. and Krska, R. (2002). Structural characterization of metabolites after the microbial degradation of type A trichothecenes by the bacterial strain BBSH 797. Food Addit. Contam 379-386.
- Molnar, O., Schatzmayr, G., Fuchs, E. and Prillinger, H. (2004). Trichosporon mycotoxinivorans sp. nov., a new yeast species useful in biological detoxification of various mycotoxins. Syst. Appl. Microbiol. 661-671.
- Schatzmayr, G., Heidler, D., Fuchs, E., Mohnl, M., Taubel, M., Loibner, A. P., Braun, R. and Binder, E. M. (2003). Investigation of different yeast strains for the detoxification of Ochratoxin A. Mycotoxin Res. 124-128.