Mycotoxins and Food Safety Concerns

Mycotoxins are a significant food safety concern in the grain supply chain. Contaminated food and feed products represent a major threat to human and animal health. These toxic fungi are present throughout distribution and have adapted to a wide range of habitats, including deserts, high salinity environments, and low and high temperature environments. There are hundreds of mycotoxins known to exist, but nearly 30 of them have been well characterized and are considered harmful to humans and animals.

The most important mycotoxins that cause severe economic and health damages are aflatoxins, fumonisins, vomitoxin/deoxynivalenol (DON), ochratoxin A, zearalenone, patulin, and T-2 Toxin (see Table 1 for additional details on mycotoxins, fungal sources, and target commodities).

Aflatoxins are likely the most widely occurring and studied mycotoxins in the world implicated with various diseases. To protect consumers from mycotoxins, many countries have implemented regulations to limit the exposure of mycotoxins in food and feed products.

Health and Economic Impact

Consumption of foods contaminated with mycotoxins can lead to serious health implications if the toxins are present at very high levels. A disease or disorder caused due to mycotoxin contamination is called mycotoxicoses. Some mycotoxins can be acutely or chronically toxic, depending on the type of toxin, dosage, age, and susceptibility (immunocompromised patient). The long-term exposure to mycotoxin-contaminated foods can increase cancer risk and suppress the immune system. Diagnosing a patient for suspected mycotoxicoses is challenging because the symptoms are similar to those caused by other pathogenic microorganisms.

Worldwide, approximately 25% of food crops are affected by mycotoxins, causing losses of billions of dollars every year. The presence of mycotoxins at levels higher than the Food and Drug Administration (FDA) limits can have an adverse effect on the economy. Grain producers and food manufacturers would suffer the consequences of the reduced marketability or recall of their products both domestically and internationally. The economic impact of mycotoxins includes loss of human and animal life, increased health care cost, reduced livestock production, losses in crops, product recalls, increased research investment, and costs associated with regulatory programs directed toward mycotoxins.
 

Field and Storage Fungi

Fungal infection and subsequent production of mycotoxins can occur at the field during crop growth or harvesting, and may continue during storage. Although it is very difficult to classify them based on origin, fungal contamination can be divided into two major groups: field fungi (e.g., Fusarium and Alternaria spp.) and storage fungi (e.g., Aspergillus and Penicillium spp.). Generally, the original source of fungi is from the field.
 

Mycotoxin Synthesis

Temperature, water, salinity, nutrient stresses, and pest infestation are important reasons for fungal infection of field crops. In general, cool and wet weather favors Fusarium toxins, while hot and humid weather favors Aspergillus toxins. High moisture content [water activity (aw)], temperature, and poor sanitary conditions are associated with fungal infection and subsequent mycotoxin synthesis in stored grain.

Fungus grows in a temperature range of 50-105°F, above 0.7aw, and a pH range of 4 to 8. It is possible to predict the type of fungal growth and subsequent mycotoxin production to some extent depending upon the type of grain, moisture content, and temperature of the stored grain. However, the conditions for mycotoxin synthesis are generally more critical and complex than those for fungal growth.

For grain handlers and food producers, it is important to monitor the temperature and relative humidity during storage at regular intervals. Relative humidity influences the moisture content of stored grain, resulting in more or less water available for fungal growth and subsequent mycotoxin synthesis. Additionally, storage fungi are more frequent in bins infested with stored product insects. These stored product insects act as potential routes for distributing fungal spores.
 

Sampling and Testing

Proper grain sampling and sample preparation are important for accurate test results. There are several testing tools available to detect and quantify mycotoxins in grain and grain-based products. Various testing tools, such as thin-layer chromatography, high-performance liquid chromatography (HPLC), gas chromatography, and enzyme-linked immunosorbent assays (ELISA) can be used depending on the needs. Since fungi can still grow and synthesize mycotoxins in a sample, samples should be properly preserved (dried, frozen, or treated with mold inhibitor) and shipped quickly for analysis to avoid variation of test results.
 

Management and Treatment

Mycotoxin content increases with delayed harvest, rain, and cool weather. Proper cleaning of harvested grain is a must to reduce mycotoxin content as mycotoxin concentration is greatest in damaged kernels and fine material. Drying harvested commodities to a safe moisture level (aw of about 0.7) and maintaining grain moisture during storage is crucial for controlling or minimizing fungal growth and subsequent mycotoxin synthesis.

Maintaining uniform grain temperatures throughout the grain mass is important to avoid moisture imbalance. This can be achieved by passing large volumes of ambient air (aeration) through the grain mass.

Detoxifying mycotoxins in grain and grain-based products is a complex and expensive process. Several detoxification methods have been developed (e.g., ammonification, ClO2, ozone, etc.) to treat mycotoxin-contaminated grain and feed products. However, there are several limitations and challenges that still remain. Most mycotoxin-contaminated grain detoxification methods are either too expensive, have safety concerns, or leave residues in the commodities that would affect end use. Therefore, preventing fungal infection, rather than trying to treat infected grain or products, is the best practice.

The CO₂-sensing technology developed in recent years is one of the most promising technologies for early detection of spoilage due to molds during grain storage. Increasing awareness among grain handlers and food producers, and encouraging them to adopt good agricultural practices, good manufacturing practices, and HACCP are the best strategies to lower health risks and economic loss.

The author is Director, Microbiology, AIB International.