Understanding the Origins of Mycotoxins in Cheese
Mycotoxins are naturally occurring toxins produced by certain molds, mainly from the Aspergillus and Penicillium genera. In the context of cheese production, these toxins can enter the food chain through two primary pathways:
- Indirect Contamination: Dairy animals, such as cows, goats, and sheep, may ingest feed contaminated with mycotoxins. Aflatoxin B1 (AFB1), a common mycotoxin in contaminated feed, is metabolized in the animal's liver into aflatoxin M1 (AFM1), which is then excreted into the milk. Since AFM1 is heat-resistant, pasteurization does not eliminate it, leading to its concentration in cheese during the cheesemaking process.
- Direct Contamination: Mold growth on the cheese itself during ripening, storage, or transport can directly produce mycotoxins. While some molds are intentionally added to cheeses like Brie, Camembert, and blue cheeses, even these strains can produce mycotoxins under certain conditions. Non-starter, or 'wild', molds from the processing environment can also introduce mycotoxigenic strains.
Which Cheeses are Most Susceptible to Mycotoxins?
Research indicates that certain types of cheese, and specific production methods, are more prone to mycotoxin contamination. Artisanal or traditional cheeses, for instance, have shown higher levels of certain mycotoxins due to less stringent production and storage controls compared to industrial processes.
- Blue Cheeses: While the Penicillium roqueforti mold gives blue cheese its characteristic flavor, some strains can produce mycotoxins such as roquefortine C (ROQ-C) and mycophenolic acid (MPA).
- Hard Cheeses: Surface contamination can be an issue with hard cheeses like Grana or Comté, as mycotoxins like Ochratoxin A (OTA) and Citrinin (CIT) can penetrate several centimeters into the product over time.
- Soft Cheeses: Fresh goat cheese, for example, has been found to be a good substrate for mycotoxin production by certain Penicillium species.
Factors Influencing Mycotoxin Formation in Cheese
Several environmental and processing factors dictate whether mold will grow and produce mycotoxins on or in cheese.
- Temperature: Temperature is a major factor. While cheese is often stored in refrigerated conditions (4–7°C) to inhibit mold growth, mycotoxins can still be produced at these lower temperatures by psychrotolerant strains. Optimal mycotoxin production typically occurs at higher temperatures (20–25°C), which can be an issue if cheese is improperly handled or stored.
- Water Activity ($a_w$): Mycotoxigenic fungi thrive in specific water activity ranges. Lowering the water activity, such as by salting, can inhibit some fungal species, but certain molds, like OTA-producing strains, are specifically adapted to salt-rich environments.
- Acidity (pH): The pH of the cheese also influences fungal growth and mycotoxin production. A dynamic microbial ecosystem of bacteria and fungi in the cheese can either inhibit or promote the growth of mycotoxigenic molds.
- Cheese Composition: The nutrient profile of the cheese, including its fat, protein, and mineral content, can either facilitate or suppress mold growth and mycotoxin synthesis. For instance, certain compounds like free fatty acids and lactic acid bacteria can inhibit mycotoxin formation.
Comparison of Mycotoxin Risks by Cheese Type
To provide clarity, the following table compares the mycotoxin risk factors across various common cheese types. It's important to note that risk can be heavily influenced by processing practices and handling, not just the cheese type itself.
| Cheese Type | Ripening Process | Potential Mycotoxins | Risk Factors | Key Contamination Route | Safety Measures |
|---|---|---|---|---|---|
| Blue Cheese | Internal mold ripening with P. roqueforti | Roquefortine C (ROQ-C), Mycophenolic Acid (MPA) | Prolonged maturation, specific strain variants | Direct mold growth | Controlled ripening conditions, using non-toxigenic starter cultures |
| Hard Cheese (e.g., Grana, Parmesan) | Long-term maturation | Ochratoxin A (OTA), Citrinin (CIT) | Surface mold contamination during ripening or storage | Direct mold growth | Monitoring surface during maturation, removing affected rind |
| Soft-Ripened Cheese (e.g., Brie, Camembert) | Surface mold ripening with P. camemberti | Cyclopiazonic Acid (CPA), other minor toxins | Strain potential, environmental control during ripening | Direct mold growth | Strict hygiene in processing plants, monitoring starter cultures |
| Fresh Cheese (e.g., Cottage, Ricotta, Fresh Goat Cheese) | Minimal to no ripening | Citrinin (CIT) | Contamination via raw milk, cross-contamination, poor handling | Indirect from milk or Direct spoilage | Using pasteurized milk, strict hygiene, proper refrigeration |
| Industrial Cheese | Standardized, controlled process | Aflatoxin M1 (AFM1) | Contaminated feed in dairy herds | Indirect from milk | Regulation and monitoring of animal feed, pasteurization |
Best Practices for Consumers and Producers
While the industry has strict regulations and testing protocols, consumers can also take steps to minimize their risk.
- For Consumers:
- Discard Moldy Spots? Unlike with some vegetables, simply cutting off the visible mold on cheese is often not enough, as mycotoxins can penetrate deeper into the product, especially in softer varieties. Discarding the entire item or a larger surrounding area is the safest approach.
- Proper Storage: Keep cheese in a clean, dry, and cool environment to prevent unwanted mold growth.
- Rotate Stock: Buy cheese as fresh as possible and do not keep it for extended periods.
- For Producers:
- Monitor Feed: The first line of defense is monitoring and regulating animal feed to minimize mycotoxin exposure to dairy cows.
- Ensure Hygiene: Implementing thorough cleaning and sanitation practices at every stage of production, from milking to storage, is critical.
- Control Conditions: Closely control environmental factors such as temperature, humidity, and water activity in ripening rooms to prevent toxigenic mold growth.
Conclusion
In conclusion, mycotoxins can be present in cheese, either through indirect contamination from animal feed or direct mold growth during production and storage. While regulatory agencies set maximum permissible limits to protect consumer health, contamination can still occur. Consumers can minimize risk by properly handling and storing cheese, and by discarding any with visible, non-intentional mold. The safety of cheese relies on a comprehensive risk management strategy, spanning from careful feed sourcing to controlled maturation processes. For further information on mitigating risks, the Neogen corporation provides resources on best practices for producers.
Key takeaways
- Mycotoxins can contaminate cheese through either contaminated animal feed (producing AFM1 in milk) or mold growth on the cheese itself during ripening.
- Industrial processes help control risk, but artisanal cheeses, which may rely on spontaneous flora, have been found to have higher mycotoxin levels in some studies.
- Temperature and moisture are key factors influencing mycotoxin production; improper storage can increase risk.
- Cutting mold off cheese is not a recommended practice for most types, as the toxins can penetrate deeper than the visible mold.
- Monitoring animal feed and hygiene during production are the most effective ways for producers to prevent mycotoxin contamination.
- Consumers should practice safe handling, proper storage, and mindful consumption to minimize mycotoxin exposure.
