Image: The Buhler food safety laboratory. Photo courtesy of Buhler


Pathogens, such as salmonella, are a key cause for concern. So too are non-declared allergens, such as gluten-containing foreign kernels in gluten-free produce, foreign bodies, and increasingly the widespread presence of mould fungi and their hazardous metabolites, referred to as mycotoxins.

Aflatoxin, deoxynivalenol (DON), zearalenone (ZEA) and ergot alkaloids are the mycotoxins creating the most concern and are common in grains such as wheat, maize, rye, barley and spelt. With some mycotoxins, such as the highly-toxic aflatoxin, the vast majority of grains are not affected, but just a few highly-contaminated kernels could make an entire lot unsafe for further use.

One example of an unsafe situation caused by aflatoxins was in 2012/2013 when dairy cows in South East Europe were fed contaminated maize. This led to some cases of unsafe levels of the highly toxic aflatoxin M1in milk intended for human consumption.

There has also been a re-emergence of ergot alkaloids in rye in Central Europe, causing the relevant authorities to revise safety assessments and some companies to insist on ultra-low commercial specifications. This underlines the need to support grain processors in their ongoing efforts to ensure safe products. Matthias Graeber, mycotoxin expert within Bühler’s Corporate Technology Group explains what the industry can do to reduce the risk of mycotoxins.

Early intervention to reduce contamination

"Pathogens, such as salmonella, are a key cause for concern"

To reduce the risk of hazardous contamination in cereal grains, processors must first follow the guidelines of good agricultural and post-harvest practice. However, extreme weather can cause plant stress, making the crop more susceptible to fungal infections.

These ongoing issues mean grain processors require solutions that ensure grain lots comply with commercial specifications and legal maximum levels of toxins. They also need to ensure any initial contamination does not spread further by removing the small percentages of hazardous grains as early as possible in the value chain.

In the case of maize, for instance, some regions have seen the crop severely hit by different mycotoxin in successive years. In response, processors have implemented advanced cleaning processes to target the affected grains, not only in mills but upstream in the chain at both grain reception facilities/grain elevators and warehouse levels, complementing the well-established, pre-cleaning processes.

Mycotoxin reduction through customised cleaning processes

While modern grain cleaning technologies can significantly reduce concentrations of mycotoxins, removing affected grains can also negatively impact the yield, meaning it’s critical to tailor cleaning processes in such a way that mycotoxin levels are reduced effectively and consistently with minimal loss of good, unaffected product. This is particularly important as there is no technology currently available that can directly detect mycotoxins in grains, in real time and non-destructively – certainly not at a product flow of many tonnes per hour.

The actual measurement of mycotoxins at the relevant levels – ranging from a few parts per billion (ppb) for aflatoxins to parts per million (ppm) for deoxynivalenol – requires processors to remove a representative sample from the product and then analyse it using commercially available antibody-based test kits or high performance liquid chromatography (HPLC) laboratory analysis. Therefore, instead of actually detecting mycotoxins, modern grain cleaning technologies target the properties that indicate the presence of a fungal contamination and thus the potential of a mycotoxin contamination.

Processing excellence in mycotoxin management

"There has also been a re-emergence of ergot alkaloids in rye in Central Europe"

Bühler partners with grain processors and world-leading researchers in mycotoxin management, such as the Institute of Sciences of Food Production (ISPA) in Italy, to develop solutions for the cleaning of mycotoxin from cereal grains and to provide conclusive data as reference case studies. The results have also enabled experts to define standard flow diagrams, incorporating elements for mechanical separation and optical sorting of grains. For example, size separation removes broken kernels from the lot, as these tend to have a higher concentration of mycotoxins.

It has also been found that very light product and dust from affected lots typically contains higher levels of mycotoxins, which can be removed through integrated or separate air aspiration systems.  Further separation of lower-density grains again decreases the mycotoxin concentration. Finally, an optical sorter, such as Bühler’s SORTEX A MultiVision, detects subtle colour defects and can distinguish anomalies in the non-visible, infrared reflectance of the cereal grains. This part of the electromagnetic spectrum can access information about chemical changes in the grains and is proven to be highly effective in identifying mycotoxin-contaminated grains.

It is understood that the larger the mycotoxin concentration in the removed product, the more efficient the cleaning process. As a result, the reduction of aflatoxin levels can then be achieved with less good product removed. Buhler has demonstrated how mycotoxin levels can be typically reduced by cleaning an aflatoxin contaminated lot of maize, in an Italian cleaning facility, running at a throughput of 20 tonnes per hour.

The results of this case study reveal the relative concentration of total aflatoxins in the fractions removed by size separation, aspiration channel, density separation and optical sorting, respectively. The product rejected by the SORTEX A optical sorter, for instance, contained an aflatoxin level of more than 1100% of the levels detected in the input material. Such high levels in the removed fractions are a direct result of utilising expert knowledge of the product properties that indicate fungal contamination, together with advanced optical sorting equipment.  This ensures an optimised high capacity product flow, robust high-speed detection of the defective product and accurate ejection. The aflatoxin level in the cleaned product was reduced by 84%.

The right solutions help to reduce risk

"Removing affected grains can also negatively impact the yield"

In addition, advanced optical sorting reliably removes foreign kernels and foreign materials, which, if undetected, can cause injury if eaten, plus lead to costly, commercially damaging product recalls and affect business relationships.

Cleaning solutions for fungal contaminations are available for a wide range of cereal grains, such as wheat, maize, barley and rye, tackling a variety of hazardous fungal contaminations including aflatoxins, DON, ZEA, and ergot alkaloids.

Extensive case studies have shown that with the right solution it is possible to reduce mycotoxins to meet the maximum safety levels in grain – permitted by legislation and/or commercial contracts – thus reducing the risk of financial losses and damaged business relationships. Furthermore, wastage is reduced, as the unnecessary removal of unaffected grains is minimised, ensuring that business-critical yields are maximised.