While the top allergies vary from country to country, the top 10 allergens remain consistent (3). The majority of the top 10 allergens are grown on farms, including soy, wheat, tree nuts, peanuts, mustard seeds, sesame seeds, and, in some regions, celery. Farmers who grow row crops, like wheat, peanuts, and soy, often grow crops in rotation and use the same equipment, storage elevators, and trucks on farm and when transferring materials to larger multifarm storage elevators. Not all farmers are trained in or are capable of fully cleaning their farm equipment for allergens. This can lead to potential cross contamination of allergenic materials with materials that are less likely to contribute to an allergic response. Consider, for example, a small handful of peanuts left in a corner of a transport vehicle and moved from the farm to an elevator—that handful of peanuts can then contaminate an entire elevator of wheat, soy, or corn.
This became a significant issue in regions where train operators were not mandated to perform cleaning for allergens or to maintain separate railcars for transportation of some highly allergenic materials.
In the last 10 years in North America, a couple of food recalls were linked to trace amounts of peanuts or peanut residue found in railcars that were emptied but not cleaned for allergens prior to being loaded with wheat that was then milled into flour (7). This put the onus on the miller or elevator operator to test each car to assure there was no contamination present. Many millers chose to forgo rail service in lieu of trucks unless there was transparency concerning the use of the railcar exclusively for grains. In the United States, the Food Safety Modernization Act (FSMA) enacted in 2011 is alleviating some concerns about cross contamination with allergens due to expectations that cleaning for allergens will be documented and transparency across the food supply system, including the transportation system.
The soils in which grains and other food sources are grown are capable of supporting the growth of more than just the plants the farmer deliberately sows. Some of the other organisms that can grow in farm fields are fungi. Some fungi capable of growing on grains, coffee, cacao, and other foodstuffs have the potential to form mycotoxins (9). Mycotoxin-forming fungi are naturally present in the environment, and they grow readily in warm and humid environments. Many of these fungi are present in the soils where grains are grown, and some are capable of forming spores, making them a persistent threat. The majority of the fungi that infect grains are Aspergillus spp., Penicillium spp., and Byssochlamys spp. Some of the most notorious fungal infections are caused by A. flavus and A. parasiticus, which produce aflatoxins. These toxins can affect humans and animals, are capable of being genotoxic, and can be deadly. The grains most commonly affected by aflatoxins are corn, sorghum, wheat, and rice. Fusarium head blight (FHB) is a common fungal disease in wheat and rye and is capable of forming neurotoxins.
Common grain infections happen in the field and in storage. Because fungal spores are present in soils, growing plants are susceptible to infection when environmental conditions allow. One fungal disease of wheat, FHB, can set in the flowers of wheat if conditions are warm, rainy, or humid during flowering. Grain elevators, where large quantities of grains are stored, have convection currents that form with the heating during the day and cooling at night of the grain in the bin. Proper storage allows for air circulation and movement of the grain in the bin. If the grain is not moved and convection currents persist, portions of the grains can form warm, high-moisture areas capable of supporting fungal growth. The fungi can form mycotoxins that, when the elevator is emptied, are spread through the entire mass of grains in the elevator.
Grains can be contaminated with many other potential mycotoxins as well, such as fumonisins, nivalenol and deoxynivalenol (DON), ochratoxin A, aflatoxins, and others (1,9). Mycotoxin levels in grains are regulated for food safety and have been for decades. Regular testing has been made simpler with advances in rapid methods that allow for screening of grains before and after elevator storage or transportation (4). This prevents fungal materials from entering mills and contaminating the mills and the food and feed streams.
Contamination by pests can include a diverse array of creatures, ranging from insects to rodents. Insects are particularly small creatures and are easily moved from field to storage to transportation vehicles because they are often smaller than the grain or because they are inside the grain body (4). Pests can impact both the quantity and quality of the grain. Although pest infestation is not generally a significant risk to human health, there are regulations limiting contamination levels. Pest infestation is best controlled early in the grain storage system. If grain is stored in a clean, well-built elevator or bin, instead of in a pile on the ground, the risks of pest infestation are lower. Fumigation of grains to eliminate insects is common in storage and transportation systems. Train cars used for movement of large quantities of grain are often treated with a fumigant “blanket” that virtually eliminates infestation or reinfestation during transportation.
As discussed previously, grains are row crops that are grown in open air environments and, thus, are subject to virtually all kinds of microbiological contamination—animals eliminate and can die in fields, birds fly over and defecate on grains, and wind-blown soil containing microbes can contaminate grains. Although most contamination levels are very low and unlikely to impact human or animal health, it is something to be cognizant of when formulating products or milling grains that could potentially be consumed without a 4–5 log kill step that would reduce possible health effects. A 4–5 log kill step uses a logarithmic scale to assess the reduction in microbes a process or treatment achieves, with the goal of reducing microbes by 10,000–100,000 times.
Microbiological contamination can be amplified if grain materials are stored under warm, humid, or wet conditions because these environmental conditions allow microbes to multiply. In addition, certain anatomical portions of the grain are more prone to contamination than others. Microbes are generally present on the surfaces of grains or in the crease of grains with that morphology. When the bran is stripped from the surface of grains and used as a concentrated source of fiber and antioxidants, this can concentrate the contamination in the finished food product. In applications in which bran is used as a large portion of the formula, products should be exposed to enough heat to reduce or eliminate the contamination (a minimum of a 4 log reduction).
In all cases, biological contamination of grains starts on the farm or in local storage in an elevator or bin. The critical element in management of these contaminants is early testing and intervention (2). As grains are moved from the farm into the storage and transportation systems, testing grains for contaminants before comingling with other grains and rejection of heavily contaminated grains is critical. Heavily contaminated grains should never make it into the transportation system. Partnering management of the transportation system with testing provides a system approach to total management of the grain system. Cleaning for allergens is still a significant risk to human health. Separation of trains or trucks used for transporting grains from those used for transporting soy or peanuts will go a long way toward reducing the risk of inadvertent contamination.
The final line of defense is testing by the final processor (either miller or food or feed manufacturer). The best case is that the materials coming into the processing plant are tested before they enter the food or feed stream and that there are clear separations between raw materials and finished products. The results of testing postmanufacturing can lead to food recalls (8). Food recalls have become more common, with a 10% year-on-year increase in total recalls in the early 2010s (5). Although most of the recalls are not related to contaminated grains, the cost of a recall to a food company is upwards of US$10 million or more and causes significant damage to a company’s reputation that is difficult to calculate (6). The profit margins for all parts of the grain supply chain are not huge, and managing the costs of contamination can put those profits at risk.