Micotoxines i Seguretat Alimentària

Understanding Mycotoxins and Food Safety

Mycotoxins are toxic secondary metabolites produced by certain fungi that can contaminate food and feed, posing serious health risks to humans and animals. This course explores the key concepts behind fungal growth conditions, the most relevant mycotoxins, their toxicological effects, and regulatory limits. By the end of the module, you will be able to identify critical control points in the food chain and understand the mechanisms of toxicity and elimination.

1. Fungal Growth Requirements: Water Activity (a_w)

Water activity (a_w) measures the availability of free water for microbial growth. Most fungi that contaminate cereals require a relatively high a_w to proliferate.

• Critical threshold: a_w > 0.7 is needed for the majority of spoilage fungi.
• Values below 0.5 generally inhibit fungal growth, while a_w = 1.0 represents pure water.
• Controlling moisture during storage (drying to a_w ≤ 0.6) is a primary strategy to prevent mycotoxin formation.

2. Major Mycotoxins and Their Toxicity

Several mycotoxins are of particular concern due to their hepatotoxic, genotoxic, and endocrine‑disrupting properties.

2.1 Aflatoxins (B1, B2, G1, G2)

Aflatoxin B1 (AFB1) is the most potent and is primarily associated with hepatotoxic and genotoxic effects. Chronic exposure can lead to liver cirrhosis and hepatocellular carcinoma.

2.2 Ergot Alkaloids

Ergotism manifests in two classic forms:

• Gangrenous ergotism: Vascular constriction leads to ischemia and tissue necrosis, potentially resulting in limb loss.
• Convulsive ergotism: Neurological disturbances (seizures, hallucinations) without the severe tissue loss seen in the gangrenous type.

Regulatory limits in the EU set a maximum of 0.05 % ergotamine in rye, which corresponds to roughly 1000 µg/kg of total ergot alkaloids.

2.3 Patulin

Patulin, commonly found in apples and derived products, is classified by the International Agency for Research on Cancer (IARC) as Group 3 – not classifiable as to its carcinogenicity to humans.

2.4 Zearalenone

Zearalenone acts as an estrogenic endocrine disruptor. In livestock, it binds to estrogen receptors, causing reproductive disorders such as infertility, reduced litter size, and altered estrous cycles.

3. Biological Factors Influencing Mycotoxin Production

Mycotoxin synthesis is not solely dependent on environmental conditions; intrinsic biological factors also play a crucial role.

• The presence of specific invertebrates and particular genetic families within a fungal species can enhance toxin biosynthesis.
• While temperature, light, and CO₂ levels affect fungal growth, they are secondary to the genetic capacity of the strain to produce toxins.

4. Metabolism and Excretion of Aflatoxins in Humans

After ingestion, aflatoxins are metabolized in the liver to both reactive (epoxide) and more water‑soluble forms. The primary route of elimination for these hydrosoluble metabolites is via the urine, with minor contributions from bile and feces.

Understanding this pathway is essential for biomonitoring programs that measure urinary aflatoxin‑M1 as an indicator of exposure.

5. Regulatory Limits and Practical Implications

Food safety authorities worldwide set maximum permissible levels for mycotoxins to protect public health. Key points include:

• EU limit for ergot alkaloids in rye: 0.05 % ergotamine (~1000 µg/kg).
• Maximum levels for aflatoxin B1 in cereals: typically 2–4 µg/kg, depending on the region.
• Patulin limits in apple products: 50 µg/kg (EU) and 100 µg/kg (US).
• Zearalenone limits in feed: 250 µg/kg for swine, 500 µg/kg for poultry.

Compliance requires rigorous sampling, analytical testing (e.g., HPLC, ELISA), and implementation of good agricultural and storage practices.

6. Summary of Key Concepts

• Water activity > 0.7 is the minimum condition for most cereal‑contaminating fungi.
• Aflatoxin B1 is hepatotoxic and genotoxic.
• Ergotism presents as gangrenous (vascular) or convulsive (neurological) forms; EU limit translates to ~1000 µg/kg alkaloids.
• Biological factors such as specific invertebrate presence and fungal genetic families influence toxin production.
• Hydrosoluble aflatoxin metabolites are primarily excreted in urine.
• Patulin is IARC Group 3 (not classifiable as carcinogenic).
• Zearalenone’s main effect is estrogen receptor binding, leading to reproductive issues in animals.

7. Frequently Asked Questions (FAQ)

What is the most effective way to reduce a_w in stored grains?

Implementing proper drying to achieve moisture content below 12 % (a_w ≤ 0.6) and using airtight storage containers are the best practices.

How can I monitor aflatoxin exposure in a population?

Urinary biomarkers, especially aflatoxin‑M1, provide a non‑invasive method for assessing recent exposure.

Are there any natural compounds that can inhibit mycotoxin production?

Certain plant extracts (e.g., essential oils from oregano or clove) have shown antifungal activity and can reduce toxin synthesis when applied during storage.

8. Further Reading and Resources

• FAO/WHO Codex Alimentarius – Guidelines for the Control of Mycotoxins in Food and Feed.
• European Food Safety Authority (EFSA) – Scientific Opinions on Aflatoxins.
• IARC Monographs – Evaluation of Carcinogenic Risks to Humans.
• Recent review: "Mycotoxin mitigation strategies in the post‑harvest chain" (Journal of Food Protection, 2023).