Ochratoxin in Foods: Health Impacts and Prevention Strategies

Ochratoxin A (OTA) is one of the most widespread and dangerous mycotoxins found in our food supply. Produced by certain species of Aspergillus and Penicillium fungi, this toxic compound quietly makes its way into everyday staples like cereals, coffee, dried fruits, wine, and spices. What makes OTA particularly concerning is its ability to damage the kidneys, suppress the immune system, and potentially cause cancer. For anyone involved in food science, agriculture, or public health, understanding how OTA contaminates food – and how to prevent it – is essential knowledge.

What is ochratoxin A? 🔗

Ochratoxin A is a chlorinated isocoumarin compound with a molecular weight of about 403.8 Da. It is a secondary metabolite – meaning it is not essential for the fungus to survive, but it is produced under certain environmental conditions. OTA is generated primarily by Aspergillus ochraceus, A. carbonarius, A. niger, and Penicillium verrucosum. These fungi thrive under a wide range of temperatures (0-37°C), which is why OTA contamination is a global problem affecting both tropical and temperate regions.

Structurally, OTA consists of an isocoumarin moiety linked to the amino acid L-phenylalanine through an amide bond. This structure is significant because the phenylalanine component allows OTA to interfere with protein synthesis in the body, contributing to its toxic effects.

Which foods are most commonly contaminated? 🔗

OTA has been detected in a wide variety of raw and processed food products. Cereal grains are the largest dietary contributor, accounting for roughly 55% of total OTA intake in many populations. Wheat, maize, barley, oats, and rice are all susceptible, especially when stored under improper conditions that favour mould growth.

Coffee is the second most significant source. OTA contamination in coffee can occur during harvesting (when fallen or overripe cherries sit on the ground), during wet processing, and during storage and transportation. The FAO has noted that OTA in green coffee is not completely eliminated during roasting, which means the toxin can persist into the final brewed cup.

Other commonly affected foods include dried vine fruits (raisins, sultanas), wine and grape juice, cocoa and chocolate products, beer, spices, nuts, and even animal-derived products like milk – since livestock consuming contaminated feed can excrete OTA into their milk.

Health impacts of ochratoxin A 🔗

Nephrotoxicity: the primary concern 🔗

The kidneys are the main target organ for OTA toxicity. Research has shown that OTA enters kidney cells through organic anion transporters located in the proximal tubules. Once inside, it triggers a cascade of harmful events including oxidative stress, inflammation, and cell death through multiple pathways such as pyroptosis (inflammatory cell death) and apoptosis (programmed cell death). Over time, this damage can lead to tubular necrosis, glomerular injury, and renal fibrosis.

Studies in animals have consistently demonstrated that chronic OTA exposure causes progressive kidney damage. In humans, patients with chronic renal insufficiency undergoing dialysis tend to have higher blood OTA concentrations compared to healthy individuals, and dialysis does not effectively reduce these levels.

Carcinogenic potential 🔗

The International Agency for Research on Cancer (IARC) has classified OTA as a Group 2B carcinogen, meaning it is “possibly carcinogenic to humans.” This classification is based primarily on strong evidence of kidney tumour development in animal models, particularly male rats. However, direct evidence linking OTA to cancer in humans remains limited and is an active area of investigation.

Other toxic effects 🔗

Beyond kidney damage and cancer risk, OTA exhibits several other harmful properties. It is immunosuppressive, meaning it can weaken the body’s defence against infections. It is also teratogenic (capable of causing birth defects in animal studies), hepatotoxic (damaging to the liver), and has been shown to cause significant oxidative damage to brain tissue. The toxin’s long half-life in humans – approximately 35 days – means that even low-level chronic exposure can lead to significant accumulation in the body over time.

Ochratoxin A and Balkan endemic nephropathy 🔗

One of the most extensively studied connections involving OTA is its proposed link to Balkan endemic nephropathy (BEN), a chronic kidney disease first identified in farming communities along the Danube River and its tributaries in southeastern Europe. BEN has been documented in parts of Bosnia and Herzegovina, Bulgaria, Croatia, Romania, and Serbia, and it is associated with an unusually high incidence of urothelial tumours of the renal pelvis and ureters.

For decades, the “mycotoxin hypothesis” proposed that chronic dietary OTA exposure was the primary cause of BEN. Several studies found that OTA was present more frequently and at higher concentrations in the food and blood of people living in BEN-endemic regions compared to non-endemic areas. However, more recent research has pointed to aristolochic acid – a plant toxin from the weed Aristolochia clematitis – as the more likely primary cause. Despite this, many researchers believe OTA may still act as a contributing factor or cofactor in the development of BEN and its associated tumours.

Stability of ochratoxin A during food processing 🔗

One of the most challenging aspects of managing OTA is its remarkable thermal stability. Unlike many biological contaminants, OTA is not easily destroyed by conventional cooking or food processing methods. This means that once a food item is contaminated, removing OTA entirely through processing is extremely difficult.

Roasting 🔗

Coffee roasting offers partial reduction. Research reviewed in a study published in Toxins indicates that commercial coffee roasting at 220-260°C can reduce OTA by about 80%, though results are highly variable depending on temperature, time, and initial contamination levels. Cocoa bean roasting at 200°C for 25 minutes achieves lower reductions – around 36-41% depending on the fraction of the bean.

Baking 🔗

Baking also reduces OTA levels, but not consistently. Studies have found that biscuit baking can reduce OTA by roughly 65%, while bread baking achieves only a 0-40% reduction. The degree of reduction depends on baking temperature, duration, and the specific recipe formulation.

Milling and separation 🔗

Since OTA tends to concentrate in the outer layers of grains, milling and dehulling can redistribute the toxin into bran and outer fractions, thereby reducing OTA in the refined flour. This makes white flour generally lower in OTA compared to whole grain products, though the bran and outer fractions then carry higher concentrations.

Extrusion 🔗

Extrusion processing – commonly used for breakfast cereals and snack foods – can partially break down OTA under the high temperature and pressure conditions involved. However, the extent of reduction varies based on processing parameters.

Regulatory limits for OTA in food 🔗

To protect consumers, various regulatory bodies have set maximum permissible levels for OTA in food products. The European Union has established some of the most comprehensive limits: 5 μg/kg for cereals, 3 μg/kg for processed cereal products, 5 μg/kg for roasted and instant coffee, 3 μg/kg for cocoa powder, and 2 μg/kg for wine.

On the international front, JECFA (the Joint FAO/WHO Expert Committee on Food Additives) has set a provisional tolerable weekly intake (PTWI) of 120 ng/kg body weight, while EFSA (European Food Safety Authority) recommends a slightly stricter limit of 100 ng/kg body weight per week. Notably, the US FDA and the Codex Alimentarius have not established specific maximum limits for OTA in coffee, though many countries enforce their own national standards.

Prevention and control strategies 🔗

Since completely removing OTA from contaminated food is not currently feasible, the emphasis is rightly placed on prevention – stopping contamination before it starts. A multi-stage approach covering pre-harvest, post-harvest, and processing interventions offers the best protection.

Pre-harvest measures 🔗

Preventing fungal colonisation in the field is the first line of defence. This includes selecting crop varieties with resistance to fungal infection, managing irrigation to avoid excess moisture, controlling insect pests (as damaged grain is more susceptible to mould), and minimising mechanical damage during harvest. Removing plant debris and maintaining clean farming equipment also reduces the fungal inoculum in the growing environment.

Proper drying and storage 🔗

Moisture control is critical. OTA-producing fungi thrive under warm, humid conditions. Rapid drying of harvested products and maintaining dry conditions during storage, transport, and processing are essential steps to minimise OTA formation. For cereals, maintaining moisture content below 14% is generally recommended. For coffee, drying cherries promptly after harvest and avoiding contact with bare soil reduces contamination risk.

Storage facilities should be well-ventilated, dry, and free from pest infestations. Temperature control is equally important – cooler storage environments slow fungal growth significantly.

Biological control agents 🔗

An emerging and promising area of OTA management involves biocontrol agents (BCAs). Certain bacteria, yeasts, and non-toxigenic (atoxigenic) fungi have shown the ability to suppress the growth of OTA-producing moulds or to directly degrade the toxin. These biocontrol organisms work through several mechanisms: producing anti-germinative compounds, competing for nutrients and space, generating volatile organic compounds that inhibit mould growth, and even directly inhibiting OTA biosynthesis pathways.

Lactic acid bacteria and specific yeast strains have also demonstrated the ability to bind or adsorb OTA in food matrices, effectively reducing the bioavailable concentration of the toxin.

Physical and chemical decontamination 🔗

When prevention fails, several post-harvest interventions can help reduce OTA levels. Physical methods include sorting and removing visibly mouldy or damaged grains, ultraviolet (UV) irradiation, and the use of adsorbents like bentonite clay or zeolite in feed and food processing to bind the toxin. Chemical approaches include ozonation and treatment with certain alkaline substances – for example, adding baking soda during food processing has shown potential to enhance OTA degradation under heat.

HACCP-based food safety systems 🔗

Integrating OTA monitoring into Hazard Analysis and Critical Control Points (HACCP) systems is essential for food manufacturers. Codes of practice developed by organisations like the FAO and Codex Alimentarius provide guidelines specifically designed to prevent and reduce OTA contamination at every stage of the food chain – from the farm to the cup or plate.

Detection and monitoring 🔗

Effective OTA management also depends on reliable detection methods. Modern analytical techniques include high-performance liquid chromatography (HPLC) with fluorescence detection, enzyme-linked immunosorbent assays (ELISA) for rapid screening, and increasingly sensitive mass spectrometry methods. Advances in molecular assays and biosensor technology are making it possible to detect OTA at ever lower concentrations, enabling better surveillance across global supply chains.

Regular monitoring of raw materials, intermediate products, and finished goods is necessary to ensure compliance with regulatory limits and to protect consumer health.

The bigger picture: why OTA management matters 🔗

OTA contamination is not just a food safety issue – it carries significant economic consequences as well. When food products exceed regulatory limits, they must be removed from the market, causing financial losses for producers and exporters. This disproportionately affects developing countries where climate conditions favour fungal growth and where resources for prevention infrastructure may be limited.

Climate change is expected to exacerbate the problem. Rising temperatures, shifting rainfall patterns, and increased humidity in certain regions could expand the geographic range of OTA-producing fungi and increase contamination rates. This makes investment in prevention, monitoring, and research more important than ever.

What do you think? With OTA found in so many everyday foods – from your morning coffee to the bread on your table – how confident are you in the safety of your own food supply? And given the limitations of food processing in eliminating this toxin, should governments set stricter regulatory limits, or is the emphasis better placed on improving agricultural and storage practices at the source?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC10819544/
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC11620267/
3. https://www.fao.org/food/food-safety-quality/a-z-index/coffee/en/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC8539333/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC4247821/
6. https://www.tandfonline.com/doi/full/10.1080/02652030500309368
7. https://pubs.acs.org/doi/10.1021/acs.chemrestox.8b00291
8. https://academic.oup.com/ijfst/article/60/2/vvaf140/8203242
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC11355758/