Understanding Ochratoxin A
Ochratoxin A (OTA) is a mycotoxin produced by molds, particularly from the Aspergillus and Penicillium genera. It is known to have nephrotoxic, carcinogenic, and other harmful effects on humans and animals, and has a long half-life in humans of about 35 days. OTA is found in a wide range of products globally, including cereals, dried fruits, coffee, cocoa, wine, and beer. Due to its chemical stability, simply cooking or processing food at standard temperatures will not eliminate it completely. The best defense is a multi-pronged approach involving prevention and targeted decontamination techniques at different stages of the food supply chain.
Prevention as the Primary Strategy
The most effective way to manage OTA is by preventing its formation in the first place, using good agricultural and storage practices.
- During Harvest: Timely harvesting and the use of dry containers minimize the chances for fungal growth. Sorting and discarding visibly moldy items can also significantly reduce contamination.
- Proper Drying: Rapid and efficient drying of crops after harvest is critical to reduce moisture content, which is a key factor for mold growth and OTA production.
- Optimized Storage: Mycotoxigenic fungi require specific conditions, like warmth and high humidity, to produce mycotoxins. Storing products like cereals and spices in dry, controlled environments is essential to inhibit fungal proliferation. For example, controlling temperature and carbon dioxide levels in storage can effectively suppress fungal activity.
Physical Methods for Ochratoxin A Reduction
Once contamination has occurred, a number of physical methods can be employed to reduce OTA levels, though their effectiveness varies based on the food matrix and processing conditions.
Separation and Cleaning
- Sorting and Cleaning: This involves removing foreign material and damaged grains. In cocoa beans, for instance, OTA is concentrated in the shells, so shelling can significantly reduce levels in the final product. Simple washing with water can also achieve modest reductions in some foods.
- Milling: During the milling of grains like wheat, OTA is primarily concentrated in the outer bran and germ layers. Removing these fractions during milling can lower OTA levels in the refined flour, though it can also concentrate the toxin in the by-products.
Heat Treatments
OTA is thermally stable, but prolonged exposure to high temperatures can degrade it, though potentially creating new degradation products.
- Roasting: Roasting coffee beans at very high temperatures (over 200°C) can reduce OTA levels by a significant amount. The extent of reduction is dependent on temperature and roasting time.
- Extrusion: This process combines high temperature, pressure, and shear force. Studies have shown it can reduce OTA in cereals, with the reduction influenced by moisture content and temperature.
Radiation and Plasma
- Gamma Radiation: This technique can degrade OTA, with efficiency being dose-dependent. However, its use is limited by cost and the risk of modifying the food's physical and chemical properties.
- Cold Plasma: An emerging technology that can effectively degrade OTA on surfaces without high heat, though specific process conditions are critical for efficacy.
Chemical and Biological Methods
Chemical Approaches
Chemical methods focus on destroying the toxin's structure but can have side effects on food quality.
- Ozonation: Ozonation is an effective oxidation method that degrades OTA and leaves no residue, but careful dosing is required to avoid negative impacts on food quality, flavor, and nutrients.
- Alkaline Hydrolysis: Treating products with alkaline compounds like sodium hydroxide can break down OTA. However, this process often compromises taste and nutritional value.
Biological Approaches
These methods use microorganisms or enzymes to remove or break down OTA, offering a safer and more specific alternative.
- Microbial Bioadsorption: Lactic acid bacteria (LAB) and certain yeasts can bind OTA to their cell walls, removing it from liquid products like wine or juice. This mechanism relies on adsorption rather than degradation.
- Enzymatic Degradation: Using enzymes, like specific amidohydrolases from bacteria, can effectively break down OTA into less or non-toxic compounds, such as ochratoxin α (OTα). This is a highly promising and targeted approach for detoxification. The enzyme can be used directly or produced by microbes. For example, some Aspergillus species produce enzymes capable of high-efficiency OTA degradation.
Ochratoxin A Decontamination Method Comparison
| Method Category | Examples | Typical Reduction | Impact on Food Quality | Practicality/Cost |
|---|---|---|---|---|
| Physical | Cleaning, Sorting | Modest to High (depending on location of toxin) | Low, if targeted | High, routine practice |
| Milling (Fractioning) | High (in refined flour) | Concentrates toxin in by-products | High, common practice | |
| High-Temp Roasting | High (e.g., in coffee) | Can alter flavor and nutrition | High, standard industrial process | |
| Adsorption (e.g., carbon) | High (in liquid) | Non-specific binding, can affect flavor | Moderate, requires additives | |
| Gamma Irradiation | Moderate to High (moisture dependent) | Can affect nutrients | High cost, restricted application | |
| Chemical | Ozonation | High | Potential for quality changes | Moderate, requires specialized equipment |
| Alkaline Hydrolysis | High | Significant negative impact on taste/nutrition | Low, not recommended for food | |
| Biological | Bioadsorption (LAB, Yeast) | Moderate to High (in liquid) | Minimal impact on food matrices | High, used in brewing/fermentation |
| Enzymatic Degradation | High (requires specific enzymes) | Minimal negative impact | Emerging technology, high efficiency |
Conclusion
Can ochratoxin A be removed from food? Yes, to a significant extent, using a combination of proactive prevention and various post-harvest techniques. However, achieving 100% removal is often not feasible due to the toxin's stability. The most effective strategy combines good agricultural and manufacturing practices to prevent contamination, along with targeted methods like high-temperature roasting for certain products or biological treatment for liquid goods. Given the long half-life of ochratoxin A in humans and its health implications, continued research into safe and highly effective removal methods, such as enzymatic degradation, is vital for global food safety. For example, the development of biocontrol agents, like yeasts that occur naturally on crops, is a promising and environmentally friendly strategy to control toxigenic fungi.
