Maize, the world’s main cereal crop and a staple in the diets of a third of the global population, is susceptible to a naturally occurring poison called aflatoxin. Long-term exposure to aflatoxin has been found to cause cancer and exposure during early years has been shown to contribute to stunting in children. Worldwide, aflatoxin is estimated to be responsible for up to 155,000 cases of liver cancer a year. Globally, 160 million children suffer from stunting.1 Aflatoxin is recognized by the Food and Agriculture Organization, the World Health Organization and other public health bodies as a major food safety and security challenge.
Produced by a fungal mold, aflatoxin is colorless and odorless, making it difficult to detect. Yet as few as 2 highly contaminated grains in 10,000 can render an entire batch unsafe. Identifying and removing aflatoxin-contaminated grains is a major challenge. Today’s cleaning processes are imprecise, meaning that many tons of good grain are thrown away along with the contaminated grain, while some contaminated grains still slip through.
Today, advances in data science and digital technologies are making possible more precise solutions that were not previously feasible. LumoVision, developed by the Swiss technology firm Bühler, is a data-driven optical sorting system for maize that improves significantly on current cleaning practices and has the potential to make a major contribution to addressing the aflatoxin challenge.
A major food safety hazard
Aflatoxin belongs to the group of natural poisons known as mycotoxins. All mycotoxins are a risk to human health, but aflatoxin poses the highest risk. Five types of aflatoxin are linked to maize: B1, B2, G1, G2 and M1. Of these, aflatoxin B1 is the most toxic. Aflatoxins are produced by the Aspergillus flavus and Aspergillus parasiticus strains of fungus. Aspergillus grows best in hot and humid conditions or where grain is stored in a high moisture environment. Plants that have been stressed by extreme weather conditions, such as drought, or that have been subject to insect attack, are more susceptible to such fungal infections. Aflatoxin is also found in other grains, but it is maize – a food staple for millions of people in sub- Saharan Africa, Southeast Asia and Latin America – that is most vulnerable to contamination.
In 2015, the World Health Organization confirmed aflatoxin as the most dangerous chemical food safety hazard.2 According to a report by the International Agency for Research on Cancer, 0.5 billion people in developing countries are at risk of chronic exposure to aflatoxins throughout their lifetimes.3 The same report has established a connection between aflatoxin poisoning and stunting in children. Children in countries that rely on a maize-based diet are exposed regularly to the poison either through the food they eat themselves or, as infants, through their mother’s milk. Aflatoxin M1, a less toxic form of aflatoxin B1, can also be passed to humans through milk from cattle that have been fed on contaminated maize. It has also been found in the livers and eggs of chickens that have eaten contaminated grains.
Current regulation and management
Most countries have legislation in place setting maximum permitted quantities for mycotoxins and specifically for aflatoxins in food. These range from 2 parts per billion (ppb) in food for adults and 0.1 ppb for cereal-based baby food in the European Union, to 10 ppb in Kenya. Limits for Aflatoxin M1 in milk range from 0.05 ppb in Europe and 0.5 ppb in US. Aflatoxin is the only mycotoxin for which there are also legal limits for animal feed as well. In the EU, the limit ranges from 5 to 20 ppb. In other regions the limits for feed ranges from 20 ppb for dairy cattle in US to 300 ppb for finishing cattle.
Meeting these regulations is, however, a challenge. Aflatoxin is not destroyed through cooking or other thermal processing. As it is not possible to eradicate the toxin in any single step, it has to be tackled along the whole value chain. Good agricultural practices, such as careful seed selection, crop rotation, and proper application of fungicides help, as does thorough drying and proper storage, with silos that are well ventilated to control moisture content levels.
Bühler’s senior research engineer for digital technologies, Ben Deefholts feeding corn into the new LumoVision optical sorter
A camera on each side of the optical sorter will capture aflatoxin infected grains, detected through fluorescence
At the mill, a combination of mechanical separation and optical sorting is used to remove grains that show signs of fungal infection. Broken kernels are sieved out, contaminated dust is removed, and lighter or shriveled kernels separated. An optical sorter is then used to remove discolored and drier kernels.
Bühler’s own case studies have shown that each of these methods contributes to an overall reduction in mycotoxin contamination.4 However, these processes do not eradicate aflatoxin altogether. Some grains show no external signs of infection and some indicators may be caused by other fungi that cause no toxin. With no consistent visible difference between the kernels that are contaminated and those that are not, the only way to be entirely sure is to send a sample to a laboratory for analysis. This process is time consuming and also hampered by the fact that aflatoxin occurs in irregular hotspots. In a truckload of grain, samples taken from different areas of the load will reveal widely divergent values. As a result, even with lab testing there is a good chance of missing contaminated grains.
In some regions of the world, high levels of contamination go unnoticed altogether. A study by the International Food Policy Research Institute funded by the Bill & Melinda Gates Foundation showed that the contamination of aflatoxin in maize in Kenya in 2010 was alarming – 30 to 40% of maize collected from farmers had levels greater than 10 ppb.5 Likewise, testing of 600 maize samples from principle retail markets in Rwanda showed means between 8 and 25 ppb.6 In India, average Aflatoxin B1 contamination in cattle feed has been found to be 32 ppb.7 As a consequence, 38% of samples of popular brands of packed milk in Indian markets were found to exceed the maximum permitted limit.8
Along with the ongoing health risk, aflatoxin represents a serious business risk for farmers, traders and food processors as current techniques achieve a reduction in toxin levels of between 60 and 90% with total yield losses varying between around 5 and 25%. Furthermore, the risk is growing as climate change brings higher temperatures to more regions. There have already been documented cases in Serbia, Italy, Spain, and Hungary.
LumoVision: An innovative solution
Bühler has been working on solutions for reducing aflatoxin since it was first discovered in the 1960s. The current solution is based on observations, first made in the 1970s, that
bright green yellow fluorescence is associated with aflatoxin contamination in maize. The Food and Agriculture Organization has since recommended fluorescence as a presumptive test for aflatoxin in maize.9 However, it is only with today’s technology and innovation that it has been possible to design a system that can apply this test at industrial speeds of processing.
During an outbreak of aflatoxin contamination in Italy in 2013, some of Bühler’s customers began using fluorescence as a test for contamination. Clean grains fluoresced a blue color under ultraviolet light, whereas grains that were tested and found to be contaminated with aflatoxin fluoresced a greenish color. The cause of the fluorescence is a substance called kojic acid, which is produced by the Aspergillus fungus at the same time as it produces aflatoxin.10
With this much more specific indicator of contamination, Bühler engineers have been able to design a sorting machine that can accurately detect and identify, at industrial speeds, the precise difference in color between contaminated and healthy grains. Using high sensitivity cameras and a powerful LED- based UV lighting system, it is possible to target the specific green color associated with the presence of aflatoxin. The new lighting and camera system were incorporated into a modified sorter and installed for trials in an industrial maize plant in December 2017. After adjustments, the new system achieved a stable reduction in aflatoxin contamination levels averaging 85-90% with a yield loss of less than 5%.
In addition, a cloud-based digital service is in development, using infrastructure provided by Microsoft, to predict in real- time the risk of contamination in any given batch of maize. Data gathered by the camera about each grain is combined with more general risk data related to the batch, allowing the machine to assess the overall level of risk of contamination and automatically stop and start sorting. If the risk is particularly high, the customer is sent an alert, allowing them to take additional precautions. If the maize is assessed to be clean and the overall risk as small, the machine can decide it is safe to halt sorting. As soon as the machine identifies aflatoxin in the product again, or a higher level of risk, sorting is automatically resumed. Decision making happens on a ‘per- grain’ basis in less than 100ms, at industrial grade throughputs of 10-15 tons per hour.
With the new cloud-based system constantly monitoring the product flow and assessing risk, yield losses are reduced to almost zero, while the safety of the final product is assured.
Improving food safety and reducing economic risk
LumoVision provides a significant improvement on previous systems, enabling precision processing that reduces the risk of aflatoxin contamination while reducing food waste and business risk. Using LumoVision should result in more consistent cleaning performance and a reduction in the losses associated with the current cleaning processes. Bühler is working with different partners to further test and validate the technology for maize and other grains.
Beyond its potential to reduce the economic impacts of aflatoxin, LumoVision can make a major contribution to reducing the health impacts in less affluent communities in Africa, India and South East Asia. Here the challenge is to create partnerships with NGOs and government organizations to allow access to the technology where it is really needed. This would be followed up with a program to provide local cleaning stations throughout these regions, in combination with comprehensive educational programs covering good agricultural practices and good post-harvest handling. Together, these measures can save lives, contribute to the healthy development of children, and build prosperous communities.
Aflatoxin is a complex problem that no one player in the value chain can solve alone. However, as a leader in food processing systems, Bühler is proud to make a contribution toward tackling this challenge. As the world’s population increases and economic and environmental conditions change, sustainable food processing is no longer just a matter of corporate social responsibility; it is now also the key to successful business. LumoVision is just one of the innovative digital services that Bühler is currently developing with technology partner Microsoft to meet these challenges.
- International Agency for Research on Cancer (IARC), Press release 242, 2016 https://www.iarc.fr/en/media-centre/pr/2016/ pdfs/pr242_E.pdf
- WHO Estimate of the Global Burden of Foodborne Disease. 2015.
http://apps.who.int/iris/bitstream/ handle/10665/199350/9789241565165_eng.pdf?sequence=1 reference for WHO
- Wild, Christopher P. et al. (eds.). 2015. Mycotoxin control
in low- and middle-income countries. IARC Working Group Reports 9. https://www.iarc.fr/en/publications/pdfs-online/wrk/wrk9/IARC_ publicationWGR9_full.pdf
- Slettengren K. et al. 2017. Aflatoxin reduction in maize by advanced grain cleaning solutions. 1st MycoKey Conference, 11-14 September 2017, Ghent, BE (P85). : http://www. buhlergroup.com/global/en/process-technologies/food-safety. htm#.Wtnfg4huaUk
- International Food Policy Research Institute (IFPRI), Press release 2011, http://www.ifpri.org/news-release/new-study- documents-spread-aflatoxins-kenya
- Nishimwe, Kizito et al. 2017. An initial characterization of aflatoxin B1 contamination of maize sold in the principal retail markets of Kigali, Rwanda. Food Control (73): 574-580. https://www.k-state.edu/phl/what-we-do/An%20 initial%20characterization%20of%20aflatoxin%20B1%20 contamination%20of%20maize%20sold.pdf
- Kotinagu, Korrapati et al. 2015. Assessment of aflatoxin B1 in livestock feed and feed ingredients by high-performance thin layer chromatography. Veterinary World. 8(12): 1.396–1399 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4774816/
- Siddappa, Vinutha et al. 2012. Occurrence of aflatoxin M1
in some samples of UHT, raw & pasteurized milk from Indian states of Karnataka and Tamilnadu. Food and Chemical Toxicology 50 (11): 4158-4162. https://www.sciencedirect.com/science/article/pii/ S027869151200614X
- Shotwell, O. L. et al.1974. Aflatoxin: Distribution in contaminated corn. Cereal Chemistry 51: 492-499.
Shotwell, O. L., et al. 1975. Aflatoxin occurrence in some white corn under loan, 1971. III. Association with bright greenish- yellow fluorescence in corn. Cereal Chemistry 52: 670-677. Shotwell, O. L., and C.W. Hesseltine. 1981. Use of bright greenish-yellow fluorescence as a presumptive test for aflatoxins in corn. Cereal Chemistry 58: 124-127.
Shotwell, O. L. 1983. Aflatoxin detection and determination in corn. In Aflatoxin and Aspergillus flavus in corn, U.L. Diener, R.L. Asquith and J.W. Dickons, eds. Southern Cooperative Series Bulletin 179. Alabama Agricultural Experiment Station. Auburn, Alabama, USA. pp. 38-43.
- Marsh, P. B. et al. 1969. Mechanism of formation of a fluorescence in cotton fiber associated with aflatoxins in the seeds at harvest. Journal of Agricultural and Food Chemistry 17: 468-472.
By Stuart Bashford, Beatrice Conde-Petit, Ben Deefholts