Toxigenic Fungi And Fungal Mycotoxins In Food- An Overview
Fungal mycotoxins are toxic compounds that are naturally produced by certain types of moulds (fungi) that grow on food and feed products under warm and humid conditions. They are secondary metabolites that have no apparent function in the normal metabolism of fungi, but they can cause a variety of adverse health effects and pose a serious health threat to both humans and livestock.
Mycotoxins can contaminate food and feed at different stages of the food chain, from pre-harvest to post-harvest, during storage, processing and feeding. They can affect a wide range of crops and foodstuffs, such as cereals, nuts, spices, dried fruits, coffee beans, milk and dairy products. Most mycotoxins are chemically stable and survive food processing.
Several hundred different mycotoxins have been identified so far, but the most commonly observed mycotoxins that present a concern to human health and livestock include aflatoxins, ochratoxin A, patulin, fumonisins, zearalenone and nivalenol/deoxynivalenol. These mycotoxins have different chemical structures, biological properties and toxic effects.
The effects of some food-borne mycotoxins are acute, with symptoms of severe illness appearing quickly after consumption of contaminated food products. Other mycotoxins have long-term effects on health, such as immune deficiency, cancer, organ damage and reproductive disorders. The severity of the effects depends on several factors, such as the type and amount of mycotoxin ingested, the duration and frequency of exposure, the age, health and nutritional status of the individual, and the possible interactions with other toxins or pathogens.
Mycotoxins can also cause economic losses for farmers and food industries due to reduced crop yields, lower quality of products, increased costs of testing and monitoring, decreased animal performance and productivity, increased veterinary expenses and trade barriers.
Therefore, it is important to prevent and control the occurrence of mycotoxins in food and feed products by adopting good agricultural practices (GAP), good manufacturing practices (GMP), good storage practices (GSP) and good hygiene practices (GHP). It is also essential to monitor the levels of mycotoxins in food and feed products by using reliable detection and analysis methods. Furthermore, it is necessary to establish international standards and regulations to limit the exposure to mycotoxins from certain foods based on scientific risk assessments.
Toxigenic fungi are fungi that produce toxic secondary metabolites called mycotoxins. These fungi can infect various crops and cause plant diseases, reduce yield and quality, and pose a serious threat to human and animal health. Toxigenic fungi belong to different genera, such as Aspergillus, Penicillium, Fusarium, Claviceps, Alternaria and others. Each genus may contain several species and strains that differ in their host range, pathogenicity and mycotoxin production.
Some of the most important crops that are affected by toxigenic fungi are cereals (such as wheat, maize, rice, barley and oats), oilseeds (such as soybean, sunflower and peanut), fruits (such as grapes, apples and pears), nuts (such as pistachio, almond and walnut), spices (such as chili peppers, black peppers and coriander) and coffee. These crops may be contaminated by one or more mycotoxins, depending on the fungal species and environmental conditions. Some of the most common mycotoxins are aflatoxins, ochratoxin A, patulin, fumonisins, deoxynivalenol and trichothecenes.
The impact of toxigenic fungi and mycotoxins on crops is influenced by many factors, such as climate, soil, crop variety, cultivation practices, harvesting methods, storage conditions and transportation. Climate is a key factor that affects the fungal growth, infection and toxin production. Changes in temperature, moisture, CO2 levels and extreme weather events can alter the distribution, diversity and activity of toxigenic fungi and increase the risk of mycotoxin contamination. For example:
- Higher temperatures can favor the growth of Aspergillus species and aflatoxin production in maize and peanuts.
- Drought stress can increase the susceptibility of crops to Fusarium species and fumonisin production.
- Elevated CO2 levels can enhance the biomass and toxin production of Fusarium species in wheat.
- Heavy rainfall can increase the infection of grapes by Aspergillus species and ochratoxin A contamination.
To prevent or reduce the impact of toxigenic fungi and mycotoxins on crops, several strategies can be adopted at different stages of the food chain. These include:
- Breeding or selecting crop varieties that are resistant or tolerant to fungal infection and mycotoxin contamination.
- Applying good agricultural practices (GAP) such as crop rotation, irrigation management, pest control and timely harvesting.
- Using biological control agents such as antagonistic microorganisms or natural compounds that can inhibit or degrade toxigenic fungi or mycotoxins.
- Implementing good manufacturing practices (GMP) such as cleaning, sorting, drying and storing crops under optimal conditions.
- Applying physical, chemical or biological treatments to remove or detoxify mycotoxins from contaminated crops or products.
- Developing rapid and reliable methods for detecting and monitoring toxigenic fungi and mycotoxins in crops and products.
Toxigenic fungi and mycotoxins are a global challenge that requires a multidisciplinary approach involving researchers, farmers, food industry, consumers and policymakers. By understanding the ecology, genomics, distribution and prediction of toxigenic fungi and mycotoxins in a changing climate scenario, we can develop more effective prevention and control measures to ensure food safety and security.
Mycotoxicoses refer to the diseases or illnesses caused by the consumption of food or feed contaminated with fungal mycotoxins. The epidemiology of mycotoxicoses involves the study of the occurrence, distribution, and determinants of these diseases in populations. Here are some key points about the epidemiology of mycotoxicoses:
- Global prevalence: Mycotoxicoses are prevalent worldwide and can be found in both developed and developing countries. However, the incidence and severity of mycotoxicoses may vary depending on the geographic location, climatic conditions, agricultural practices, food storage and processing methods, dietary habits, and susceptibility of the exposed populations.
- Outbreaks: Several outbreaks of mycotoxicoses have been reported in history, affecting humans and animals with various clinical manifestations. Some examples are:
- St. Anthony`s fire: A disease caused by ergot alkaloids produced by Claviceps purpurea that infected rye and other cereals in Europe during the Middle Ages. It resulted in thousands of deaths and symptoms such as gangrene, convulsions, hallucinations, and abortion.
- Alimentary toxic aleukia: A disease caused by trichothecenes produced by Fusarium species that contaminated wheat and other grains in Russia during World War II. It resulted in several deaths and symptoms such as skin necrosis, hemorrhage, leukopenia, and bone marrow degradation.
- Turkey X disease: A disease caused by aflatoxins produced by Aspergillus flavus that contaminated peanut meal used as animal feed in England in 1960. It resulted in the death of thousands of turkeys and other farm animals with symptoms such as liver damage, jaundice, and hemorrhage.
- Balkan endemic nephropathy: A chronic kidney disease caused by ochratoxin A produced by Aspergillus and Penicillium species that contaminated cereals and other foods in some regions of Bulgaria, Romania, Yugoslavia, and Turkey. It resulted in renal failure, urinary tract tumors, and increased risk of cancer.
- Risk factors: Some factors that may increase the risk of exposure to mycotoxins and the development of mycotoxicoses are:
- Environmental conditions: High temperature and humidity favor the growth of toxigenic fungi and the production of mycotoxins on crops during pre-harvest, post-harvest, storage, and transportation stages. Climate change may also affect the distribution and diversity of toxigenic fungi and their mycotoxins.
- Food contamination: The presence of toxigenic fungi on food does not necessarily indicate the presence of mycotoxins, as not all strains are capable of producing them. Conversely, the absence of visible mold on food does not guarantee the absence of mycotoxins, as they may remain long after the disappearance of mold. Moreover, some mycotoxins may be resistant to physical, chemical, or biological treatments applied to food to reduce microbial contamination or improve quality.
- Dietary habits: The consumption of staple foods that are susceptible to fungal infection and mycotoxin contamination, such as cereals, grains, nuts, spices, fruits, vegetables, dairy products, meat products, etc., may increase the exposure to mycotoxins. The intake of multiple foods contaminated with different mycotoxins may also result in additive or synergistic effects on health.
- Susceptibility: The effects of mycotoxins on health may depend on the dose, duration, frequency, route, and timing of exposure, as well as on the age, gender, genetic background, nutritional status, immune status, co-infections, co-exposures to other toxins or drugs, etc., of the exposed individuals or animals.
Mycotoxins can cause a variety of adverse health effects in humans and animals, depending on the type and amount of mycotoxin ingested, the duration and frequency of exposure, the susceptibility and nutritional status of the individual or animal, and the interaction with other environmental factors. The effects of mycotoxins can be classified into four categories: acute, chronic, mutagenic and teratogenic.
- Acute toxicity is the most common and obvious manifestation of mycotoxin exposure, resulting from the ingestion of high doses of mycotoxins in a short period of time. Acute toxicity can cause severe damage to the liver and kidney, as well as gastrointestinal, neurological, hematological, immunological and respiratory disorders. In some cases, acute toxicity can be fatal. For example, aflatoxin B1 is one of the most potent hepatotoxins and carcinogens known, and can cause acute liver failure and death. Similarly, deoxynivalenol (DON) or vomitoxin can induce vomiting, nausea, diarrhea and abdominal pain.
- Chronic toxicity is the result of long-term exposure to low or moderate doses of mycotoxins, which can accumulate in the body and cause cumulative effects. Chronic toxicity can lead to various chronic diseases, such as cancer, liver cirrhosis, kidney dysfunction, reproductive disorders, growth retardation, immune suppression and allergic reactions. For instance, ochratoxin A (OTA) is a nephrotoxin and a carcinogen that can cause kidney tumors and chronic interstitial nephritis. Fumonisins are neurotoxins and carcinogens that can cause neural tube defects in infants and esophageal cancer in adults.
- Mutagenic toxicity refers to the ability of some mycotoxins to alter the genetic material of cells and cause mutations that may lead to cancer or other genetic diseases. Mutagenic toxicity can affect both somatic cells and germ cells, and can be transmitted to offspring. Some examples of mutagenic mycotoxins are aflatoxins, OTA, patulin and sterigmatocystin.
- Teratogenic toxicity is the ability of some mycotoxins to interfere with the normal development of the embryo or fetus and cause birth defects or malformations. Teratogenic toxicity can occur when pregnant women or animals are exposed to mycotoxins during critical periods of gestation. Some examples of teratogenic mycotoxins are zearalenone, fumonisins and trichothecenes.
The clinical manifestations of mycotoxins vary widely depending on the type and combination of mycotoxins involved, as well as the host factors that influence the susceptibility and response to exposure. Therefore, it is important to identify the sources and routes of exposure to mycotoxins in food and feed, as well as to monitor their levels and effects on human and animal health.
In this section, we will provide some detailed information on five common mycotoxins that can contaminate food and cause health problems: aflatoxins, ochratoxin A, patulin, fumonisins, and deoxynivalenol.
- Aflatoxins are potent mycotoxins produced by certain Aspergillus molds, such as A. flavus, A. parasiticus, A. nomius, A. pseudotamarii and A. ochraceoroseus.
- The most common types of aflatoxins are B1, B2, G1 and G2. Aflatoxin B1 is the most toxic and carcinogenic compound that can cause liver cancer, reproductive problems, immune suppression and death.
- Aflatoxin M1 is a metabolite of aflatoxin B1 that can be found in milk of animals that consume contaminated feed.
- The foods most susceptible to aflatoxins include peanuts, corn, tree nuts (such as Brazil nuts and pistachios), and some small grains (such as rice).
- The European Union has set a maximum limit of 2 µg/kg for aflatoxin B1 and 0.05 µg/kg for aflatoxin M1 in food. The FDA has published action levels for aflatoxin in food and feed ranging from 20 to 300 µg/kg depending on the commodity and the intended use.
- Ochratoxin A (OTA) is a toxin produced by A. ochraceus, A. carbonarius and Penicillium verrucosum.
- OTA is mainly associated with barley, coffee, cocoa, vine fruits, spices and beverages.
- OTA targets the kidney and can cause kidney damage, urinary tract tumors and chronic interstitial nephropathy. It is also considered a possible human carcinogen by the International Agency for Research on Cancer (IARC).
- OTA can persist in animal tissues for a long time even after slaughtering. It can also be transmitted through breast milk.
- The European Union has set a maximum limit of 5 µg/kg for OTA in cereals and cereal products and 10 µg/kg for dried vine fruits. The FDA has not established regulatory limits for OTA in food but has issued guidance levels for OTA in green coffee beans (20 µg/kg) and roasted coffee (10 µg/kg).
- Patulin is a toxin produced by Penicillium expansum, Aspergillus species and Byssochlamys.
- Patulin mainly contaminates fruit and vegetable-based products, especially apples and apple products such as juice and cider.
- Patulin can cause acute toxicity symptoms such as vomiting, diarrhea, abdominal pain, fever, chronic fatigue, skin rashes, insomnia, depression and anxiety. It can also damage the gastrointestinal tract, liver and immune system.
- The European Union has set a maximum limit of 50 µg/kg for patulin in apple products intended for direct consumption or used as ingredients in other food products. The FDA has also established an action level of 50 µg/kg for patulin in apple juice.
- Fumonisins are toxins produced by Fusarium species such as F. verticillioides, F. proliferatum and Alternaria alternata f. sp. lycopersici.
- Fumonisins mainly infect corn and corn-based products but can also contaminate other grains such as wheat.
- Fumonisins can cause pulmonary edema, liver and kidney damage, neural tube defects in infants and esophageal cancer in humans. They can also cause animal diseases such as leukoencephalomalacia in horses and hepatocarcinoma in rats.
- The European Union has set a maximum limit of 2000 µg/kg for fumonisins in maize and maize products intended for direct human consumption or as an ingredient in other food products. The FDA has issued guidance levels for fumonisins in human food ranging from 2000 to 4000 µg/kg depending on the commodity and the intended use.
- Deoxynivalenol (DON) is a toxin produced by Fusarium species such as F. graminearum, F. culmorum and F. pseudograminearum.
- DON contaminates corn, wheat, oats, barley, rice and other grains and has been detected in buckwheat, flour, bread, breakfast cereals, noodles and infant foods.
- DON can cause acute toxicity symptoms such as nausea, vomiting, diarrhea, abdominal pain, throat irritation and fever. It can also impair the immune system and reduce the weight gain in animals.
- The European Union has set a maximum limit of 1750 µg/kg for DON in unprocessed cereals other than durum wheat, oats and maize and 750 µg/kg for DON in cereal-based foods for infants and young children. The FDA has published an advisory level of 1000 µg/kg for DON in finished wheat products for human consumption.
Fungal mycotoxins are low molecular weight compounds that can be detected and analyzed by various methods depending on the type, concentration and matrix of the toxin. Some of the commonly used methods are:
- Bioassay methods: These methods involve the use of laboratory animals, plants or microorganisms to test the toxicity or biological activity of mycotoxins. For example, cytological assays, skin tests, enzyme inhibition assays and immunological assays. Bioassay methods are reliable and sensitive, but they are also time-consuming, expensive and require ethical approval.
- Culture methods: These methods involve the isolation and identification of the toxigenic fungi from the food samples by using selective media, microscopic examination and biochemical tests. For example, dilution plating, direct plating, membrane filtration and most probable number (MPN) methods. Culture methods are simple and inexpensive, but they are also laborious, slow and may not reflect the actual mycotoxin content in the food.
- Immunoassays: These methods involve the use of antibodies that bind specifically to the mycotoxins and produce a measurable signal. For example, enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), immunochromatographic assay (ICA) and lateral flow immunoassay (LFIA). Immunoassays are rapid, sensitive and specific, but they may also suffer from cross-reactivity, interference and matrix effects.
- Chromatographic methods: These methods involve the separation and quantification of the mycotoxins by using different types of columns, detectors and solvents. For example, thin layer chromatography (TLC), high performance liquid chromatography (HPLC), gas chromatography (GC) and liquid chromatography-mass spectrometry (LC-MS). Chromatographic methods are accurate, precise and versatile, but they also require sample preparation, calibration and validation.
- Spectroscopic methods: These methods involve the measurement of the absorption, emission or scattering of electromagnetic radiation by the mycotoxins. For example, ultraviolet-visible (UV-Vis) spectroscopy, infrared (IR) spectroscopy, fluorescence spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Spectroscopic methods are simple, fast and non-destructive, but they may also have low sensitivity, selectivity and resolution.
- Molecular methods: These methods involve the detection and identification of the genes or proteins involved in the biosynthesis or regulation of the mycotoxins. For example, polymerase chain reaction (PCR), reverse transcription PCR (RT-PCR), restriction fragment length polymorphism (RFLP), denaturing gradient gel electrophoresis (DGGE), single-strand conformational polymorphism (SSCP) and loop-mediated isothermal amplification (LAMP). Molecular methods are sensitive, specific and rapid, but they may also require specialized equipment, reagents and skills.
The choice of the detection and analysis method for fungal mycotoxins depends on several factors such as the purpose of the analysis, the availability of resources, the type of sample and the regulatory requirements. A combination of different methods may be necessary to achieve a comprehensive and reliable assessment of the mycotoxin contamination in food.
Mycotoxin contamination in food can have serious health consequences for humans and animals, such as acute poisoning, liver cancer, immune deficiency, and birth defects. Therefore, it is important to implement prevention and control measures at different stages of the food chain, from production to consumption. Here are some of the strategies that can help reduce the risk of mycotoxin exposure:
- Pre-harvest measures: These include using resistant varieties of crops, applying good agricultural practices (GAP), managing field conditions such as moisture, temperature, and pH, and using biological and chemical agents to inhibit fungal growth and toxin production.
- Harvest measures: These include harvesting crops at the optimal maturity and moisture level, avoiding mechanical damage and insect infestation, cleaning and sorting the crops to remove moldy or damaged kernels, and drying the crops quickly and uniformly to a safe moisture level.
- Post-harvest measures: These include storing the crops in clean, dry, and well-ventilated conditions, monitoring the temperature and humidity of the storage environment, preventing pest or insect invasion, applying fungicides or preservatives if needed, and testing the crops for mycotoxin contamination regularly.
- Processing measures: These include using physical methods such as washing, milling, sorting, or dehulling to remove contaminated parts of the crops, using chemical methods such as activated charcoal or sulfur dioxide to detoxify or reduce the mycotoxins, and using thermal methods such as cooking, baking, or roasting to degrade or inactivate the mycotoxins.
- Consumption measures: These include following good manufacturing practices (GMP) and good hygiene practices (GHP) in food preparation and handling, complying with the international standards and regulations for mycotoxin levels in food products established by the Codex Alimentarius Commission based on JECFA assessments, and educating consumers about the health risks and prevention methods of mycotoxin exposure.
By implementing these prevention and control measures, it is possible to reduce the occurrence and impact of mycotoxins in food and ensure food safety and quality for humans and animals. 😊
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