While many molds are harmless, and some are even intentionally cultivated for cheesemaking, certain species can produce harmful secondary metabolites called mycotoxins. Mycotoxin contamination in cheese is a potential food safety issue that arises from two primary sources: indirect contamination from the milk used and direct contamination from mold growth during maturation or storage.
Common Mycotoxins Found in Cheese
Different types of mycotoxins can be found in cheese, depending on the fungal species involved and the contamination source. The following are some of the most commonly identified mycotoxins.
- Aflatoxin M1 (AFM1): This is a metabolite of aflatoxin B1 (AFB1), a highly toxic and carcinogenic mycotoxin produced by Aspergillus molds that contaminate animal feed, such as maize and peanuts. When dairy animals consume contaminated feed, AFM1 is excreted into their milk and can be transferred to cheese, which concentrates the toxin. AFM1 is a regulated mycotoxin in milk and dairy products worldwide due to its potential human health risks.
- Ochratoxin A (OTA): Produced by Penicillium and Aspergillus species, OTA is a nephrotoxic (kidney-damaging) and potentially carcinogenic compound. It can be found on cheese rinds and sometimes penetrates deeper into the cheese, especially during improper maturation conditions involving high salt content.
- Roquefortine C (ROQ-C): This neurotoxic mycotoxin is produced by Penicillium roqueforti, the mold used to create blue cheese. While regulated blue cheese production ensures ROQ-C levels are low and typically not a health hazard, its presence highlights the need for controlled processes.
- Mycophenolic Acid (MPA): Also produced by Penicillium species, including P. roqueforti, MPA has immunosuppressive effects. Like ROQ-C, low levels are found in blue cheeses, but controlled ripening and monitoring are essential for safety.
- Citrinin (CIT): Another nephrotoxic mycotoxin produced by Penicillium and Aspergillus species, CIT can contaminate cheese. It has been found in some cheeses, though its stability varies.
- Sterigmatocystin (STC): A precursor to aflatoxin, STC has carcinogenic, mutagenic, and teratogenic properties. It can be produced by some Aspergillus species that grow on cheese surfaces during ripening.
- Cyclopiazonic Acid (CPA): This neurotoxic mycotoxin is produced by certain Penicillium and Aspergillus species and has been detected in some cheeses.
Comparison of Mycotoxin Sources in Cheese
Cheese is a complex food matrix, and the source and concentration of mycotoxins can vary significantly based on the type of cheese and its production method. The following table illustrates the different pathways of mycotoxin contamination in various cheese types.
| Mycotoxin Pathway | Blue Cheese (P. roqueforti) | Soft-Ripened Cheese (P. camemberti) | Hard Cheese (e.g., Cheddar, Parmesan) | Spoiled Cheese |
|---|---|---|---|---|
| Mycotoxin Source | Intentional mold culture (P. roqueforti) | Intentional mold culture (P. camemberti) | Indirect (animal feed via milk) or accidental mold growth | Accidental mold growth during storage |
| Typical Mycotoxins | Roquefortine C (ROQ-C), Mycophenolic Acid (MPA) | Cyclopiazonic Acid (CPA) | Aflatoxin M1 (AFM1) from contaminated feed | Ochratoxin A (OTA), Sterigmatocystin (STC), Citrinin (CIT) |
| Risk Level (Controlled Production) | Low, due to non-toxic strains and controlled environment | Low, typically non-toxic strain used | Low, due to regulations on AFM1 in milk | High, due to uncontrolled mold growth |
| Primary Prevention | Selecting non-toxigenic starter cultures and controlled aging | Careful selection of starter cultures | Testing animal feed and raw milk for AFB1/AFM1 | Proper storage and hygiene |
| Consumer Handling | Enjoy as intended, discard if spoiled | Enjoy as intended, discard if spoiled | Enjoy as intended, can trim mold from hard cheese | Discard entirely |
How Mycotoxins Get Into Cheese
Indirect Contamination via Animal Feed
This is a significant route, primarily for AFM1. It occurs when dairy cows, goats, or sheep consume feed contaminated with mycotoxins like AFB1. The animal's liver partially metabolizes AFB1, and the resulting metabolite, AFM1, is excreted in milk. This AFM1-contaminated milk is then used to produce cheese. A key factor is that cheese production concentrates the AFM1, meaning the final cheese can have higher levels of the toxin than the milk used. This is why regulations focus heavily on monitoring AFM1 levels in milk.
Direct Contamination from Mold Growth
Another pathway is when molds grow directly on the cheese itself during the production, maturation, or storage stages.
- Intentional Molds: In mold-ripened cheeses like blue cheese or Brie, specific, typically non-toxigenic, strains of Penicillium are intentionally introduced. However, under certain conditions (temperature, aeration), these molds can still produce low levels of mycotoxins like ROQ-C. In controlled commercial settings, these levels are generally considered safe.
- Spoilage Molds: Accidental contamination from wild, toxigenic mold strains can occur at any stage, from the processing plant environment to the consumer's refrigerator. These unwanted molds can grow on the surface, especially if storage conditions are poor (e.g., too warm, too humid). In these cases, the produced mycotoxins (e.g., OTA, STC) can penetrate the cheese body, posing a health risk.
Minimizing Mycotoxin Risk in Cheese
Food producers and consumers can take several steps to minimize exposure to cheese mycotoxins.
For Food Producers
- Monitor Animal Feed: Dairy farmers must implement good agricultural and management practices to control mycotoxin levels in animal feed. Regular testing for mycotoxins like AFB1 is crucial.
- Ensure Raw Milk Quality: Continuous testing of raw milk for AFM1 and other mycotoxins ensures that the cheese production process starts with a safe ingredient.
- Good Hygiene Practices: Strict sanitation in processing and aging facilities prevents the growth and spread of unwanted, mycotoxin-producing molds.
- Control Maturation Conditions: Precise control over temperature, humidity, and aeration during cheese ripening can inhibit the growth of toxigenic molds and the production of mycotoxins by even intentional strains.
- Pasteurization: While pasteurization eliminates many spoilage organisms, mycotoxins like AFM1 are heat-stable and persist. However, pasteurization does reduce the overall microbial load and is part of a multi-faceted safety approach.
For Consumers
- Practice Proper Storage: Store cheese properly refrigerated to inhibit mold growth. Wrap cheese tightly to limit exposure to mold spores in the air.
- Inspect Before Eating: Always examine cheese for signs of spoilage, such as unusual colors, fuzzy mold growth beyond what is normal for the cheese type, or a bad odor.
- Handle Moldy Cheese Carefully: For hard, low-moisture cheeses (e.g., Parmesan), it may be safe to cut off a generous portion (at least an inch) around the moldy area, as the toxins are unlikely to penetrate deeply. However, for soft, high-moisture cheeses, the mold and its toxins can spread more easily, and the entire product should be discarded.
- Discard Spoiled Cheese: If any cheese, especially a soft cheese or a mold-ripened cheese that has been improperly stored, develops new, discolored, or fuzzy mold, it is safest to throw it away.
Conclusion
While a variety of mycotoxins can potentially contaminate cheese through multiple pathways, the risk to human health from commercially produced and properly handled cheese is generally low. Aflatoxin M1, carried over from animal feed, is a significant concern for indirect contamination and is tightly regulated. Direct contamination from spoilage molds can introduce other toxins like Ochratoxin A and Sterigmatocystin, especially if storage conditions are poor. By adhering to strict hygiene and quality control standards, producers can minimize risks at the source, and consumers can ensure safety by practicing proper storage and inspecting their cheese before consumption. For many, the low mycotoxin levels in properly produced and stored cheese are not considered a significant health hazard, but vigilance remains key to nutritional diet and food safety.
What are the mycotoxins in cheese? A Focus on Key Contaminants
For decades, Aflatoxin M1 has been the mycotoxin of most concern in dairy products due to its high toxicity and concentration through the cheese-making process. Produced by certain Aspergillus species in feed, AFM1 is transferred into milk and subsequently concentrated in cheese. Ochratoxin A, a nephrotoxic mycotoxin from Penicillium and Aspergillus, poses another threat, particularly in cheese rinds. Blue cheese, though made with controlled Penicillium roqueforti cultures, can contain low levels of mycotoxins like Roquefortine C and Mycophenolic Acid, which are not typically hazardous in commercially produced cheese but must be monitored. The potential for other mycotoxins from spoilage molds underscores the need for strict quality control.
The Role of Penicillium Roqueforti in Blue Cheese
Penicillium roqueforti is a mold intentionally used in blue cheeses to develop their distinctive flavor and texture. It is generally considered non-toxic and safe for consumption. While it can produce low levels of mycotoxins like Roquefortine C and Mycophenolic Acid, controlled maturation environments and the use of specific, monitored starter cultures keep these levels from becoming a significant health risk. Concerns typically arise from uncontrolled mold growth on spoiled or improperly stored blue cheese, not from the intentional culture in a correctly ripened product.
Comparing Cheese to Other Foods
While mycotoxin risk exists in cheese, it is generally considered a less susceptible matrix for mycotoxin production compared to other food types, notably cereals and nuts, which can have high levels of mycotoxin contamination. However, the ability of cheese to concentrate mycotoxins like AFM1 from milk is a unique factor. Mycotoxin contamination in cheese is mainly from two sources: indirect contamination from animal feed (e.g., AFM1) and direct contamination from spoilage molds. In contrast, mycotoxin contamination in crops often occurs during pre-harvesting (field) or post-harvesting (storage) due to warm and humid conditions. Good agricultural practices are crucial for all susceptible foods to minimize contamination.
