When people think about food safety risks, it is often bacteria and pesticides that come to mind. Yet one of the most persistent and unpredictable threats to food and feed safety is far less visible: mycotoxins.

These naturally occurring toxins have been present for as long as crops have been cultivated, and despite advances in agriculture and storage technology, they continue to challenge producers, grain handlers, food processors, and regulators worldwide.

What are mycotoxins?

Mycotoxins are toxic chemical compounds produced by certain moulds (fungi) that infect crops. Scientists still do not fully understand why these fungi produce mycotoxins, but the toxins can remain in grain and food products long after the fungus itself has disappeared. Hundreds of mycotoxins have been identified, each produced by different fungal species. Some, such as aflatoxins, are particularly dangerous  – aflatoxin B1 is recognised as one of the most potent naturally occurring carcinogens known.

Contamination can occur either while crops are growing in the field or later during storage. This makes mycotoxins  a unique and complex food safety challenge.

Why should we be concerned?

Most mycotoxins can cause disease when contaminated food or feed is consumed  by humans or animals. Their impact ranges from reduced  animal performance and weakened immune systems to severe illness and long-term health effects.

Unlike many biological contaminants, mycotoxins  are highly stable compounds. Once present, they are difficult to destroy using standard food-processing methods. This means that prevention and monitoring are the most effective management tools.

The challenge is further complicated by the fact that mycotoxin contamination  is both unavoidable and unpredictable. Levels can vary considerably from one season to another and from one production region to the next.

How do mycotoxins get into food?

A common misconception  is that mycotoxins are associated only with poorly stored grain. In reality,  contamination can begin long before harvest. Certain fungi infect crops during the growing season, while others become problematic during storage. Grain stored under high moisture conditions (above 14%), exposed to high humidity, elevated temperatures, or inadequate drying practices, becomes particularly vulnerable.

Environmental conditions also play a major role. Rainfall patterns, drought stress, insect damage, temperature fluctuations, and storage conditions can all influence  the development of fungal infections and the production of mycotoxins.

Can you see mycotoxins?

The simple answer is no. One of the most important lessons from mycotoxin  research is that visual appearance is not a reliable indicator of contamination. Studies conducted on maize samples have shown that grain with significant visible fungal damage may contain no detectable mycotoxins, while grain that appears relatively healthy may contain measurable toxin levels.

Similarly, grain grading results cannot  be used to predict mycotoxin content. A high-quality grain grade does not guarantee the absence of toxins, and a lower grade does not necessarily indicate their presence. The only proven way to determine whether grain or food contains mycotoxins is through laboratory testing.

How are mycotoxins detected?

Accurate mycotoxin  analysis begins long before a sample reaches the laboratory. Representative  sampling is critical because mycotoxins are often unevenly distributed within a grain lot. A poorly collected sample can yield misleading results regardless of how sophisticated the analytical method may be. Once collected, samples must be correctly prepared. Grain is milled to a particle size smaller than 1mm and thoroughly mixed to ensure that subsamples accurately represent the entire batch.

The availability of rapid screening technologies based on immunochemical techniques has increased in recent years, enabling faster testing outside traditional laboratory settings. However, keep in mind that this is a screening test to detect thepresence of the toxin, and concentrations must be verified using a quantitative analytical technique.

The gold standard is liquid chromatography coupled with tandem mass spectrometry  (LC-MS/MS). This highly sensitive technology allows laboratories to detect multiple mycotoxins simultaneously and provides the accuracy required for regulatory and food safety purposes.

Managing the mycotoxin challenge

Because mycotoxins cannot easily be removed once present, prevention remains the most effective strategy. In this regard, good storage practices are essential. Grain should be dried adequately and stored under conditions that minimise moisture accumulation and temperature fluctuations. Aeration systems help maintain uniform temperatures and reduce the risk of fungal growth.

Regular cleaning and sanitation of storage facilities and equipment are equally important. Insect pests can damage kernels and create entry points for fungal infection, making effective pest control another key component of prevention. Physical damage to grain should also be minimised during harvesting, handling and storage, as broken kernels are more susceptible to fungal invasion.

Monitoring seasonal trends

Mycotoxin contamination is dynamic and influenced by environmental conditions. As a result, ongoing monitoring is essential.

The Southern African Grain Laboratory (SAGL) surveys have demonstrated that mycotoxin prevalence and concentration levels can vary significantly between seasons and production regions. Samples collected from commercial grain deliveries across the country are analysed using an accredited multi- mycotoxin LC-MS/MS method, providing valuable insight into annual contamination trends. Such surveillance helps the grain industry identify emerging risks and adapt management strategies accordingly.

The take-home message

There is no single solution to the mycotoxin challenge. Not all mycotoxins are the same, and testing for only one toxin, such as aflatoxin B1, cannot guarantee food safety. Mycotoxin patterns change from season to season and region to region, making continual monitoring essential.

Visual inspection  cannot predict contamination,  and grain grade is not a reliable indicator of mycotoxin levels. Correct sampling, sample preparation, and laboratory analysis are the foundation of effective mycotoxin management.

Ultimately, the grain and food industries can only manage the risks they understand. Ongoing testing, surveillance, and awareness are therefore critical to protecting animal and human health. As the saying goes: We can only manage what we know.

By Wiana Louw, The Southern African Grain Laboratory NPC