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mycotoxins

    Mycotoxins

    “Mycotoxins are fungal metabolites which, when ingested, inhaled or absorbed

    They are poisonous substances, which occur naturally and are perhaps the most prevalent source of food related health risk in field crops.

    Consumption of food with high levels can be fatal.

     Long-term exposure can:

    increase cancer risk

    suppress the immune system.

    by the consumption of rye contaminated with ergot alkaloids, a known mycotoxin of Claviceps purpurea .

     Mycotoxins have plagued mankind before and since the beginning of organized crop production.

    :They attract worldwide scientific, political and economic attention because of the significant economic losses associated with impacts on human health, animal productivity and international trade.

     Unfortunately, they are also considered as potential weapons and so could enter the food chain by this route.

    since the1960’s,Over 100 000 turkeys and a large number of ducks and pheasants died.

    Aspergillus flavus was discovered in the feeds and was named aflatoxin after the fungus.

    :by vomiting, abdominal pains,pulmonary oedema, convulsions, coma, and (rarely) death.

    Notable outbreaks were the death of 3 people in Taiwan in 1967 and 100 people in India in 1974, from aflatoxin in rice and corn respectively.

    The impact of mycotoxins on human and animal health is now recognized and it is estimated that they cause high economic losses.

    For example, the annual cost in the US alone was estimated as US$1.4 billion

    Mycotoxins:The field of mycotoxins is complex and interdisciplinary. It involves 5 interrelated
    systems

    Mycotoxins and Relevant Fungi

    Filamentous fungi, taken as a whole, produce thousands of toxic compounds.

    However, the more important mycotoxins belong to species of Aspergillus,Fusarium, and Penicillium.

    aflatoxins, ochratoxin A (OTA), patulin,deoxynivalenol (DON), fumonisins, nivalenol (NIV), T2-toxin, and zearalenone (ZEA)

    Aflatoxins

    Aspergillus flavus and A. parasiticus are the main producers of aflatoxins.

    Aflatoxins B1 and B2 are produced by both species but only A. parasiticus is able to produce detectable amounts of G1 and G2.

     B and G refer to the blue and green colours observed after thin layer chromatography (TLC).

    The numerical designation is for the different mobility (Rf value) of the compounds.

    Aflatoxin M1 (M for milk) is a very important toxin in milk and products and is a minor metabolic product of these Aspergillus species.

    However, it apparently occurs mainly in dairy products as a transformation product by cows of the aflatoxin B1 contained in animal feeds.

    Aflatoxins were the first mycotoxins to have their content regulated in foodstuff.

    In fact, in all countries where regulation exists for mycotoxins, there are tolerances concentrations for aflatoxins in foods or animal feedstuffs .

    Ochratoxin A

    Ochratoxin A (OTA) is produced by particular Aspergillus and Penicillium species.

    The penicillia are probably the more important producers on grains

     In other commodities, the most common are A. carbonarius, A. ochraceus and P. verrucosum.

     OTA has been associated with Balkan endemic nephropathy, which is potentially fatal.

    Ochratoxin A

    A. ochraceus and P. verrucosum are associated with cereal products, and are the primary producers of OTA.

     P. verrucosum is more prevalent in regions with temperate, and A. ochraceus with tropical climates. A third species, A. carbonarius is associated with grape products

    OTA is found in corn, wheat, sorghum, oats, rice, and green coffee.

    corn, grapes, dried fruits and wheat is generally below 500 μg kg−1.

    Highest levels have been detected in barley, oats, wheat and corn in (a) Northern Europe, i.e., UK, Denmark, Sweden and in the Balkans (former Yugoslavia) and (b) India .

    Patulin

    Patulin is produced by different species of Aspergillus and Penicillium Byssochlamys and Paecilomyces can also be involved.

     P. expansum is the most well known for causing a blue rot of apples and is associated with patulin production in apple products. Byssochlamys spp. are note worthy as they may produce heat resistant spores which survive food processing with the potential to produce patulin in processed foods.

    a wider range of fruits and vegetables The toxin is associated with P. expansum blue rot of apples and grapes.

    Anywhere that fruit products such as juice are manufactured will have a potential problem.

     Patulin producing fungi are isolated frequently from vegetables and so products are likely to be contaminated in some cases, and similarly for silage and malt.

    It occurs frequently in the USA where the FDA operates mandatory action levels in apple juice.

    Fumonisins, trichothecenes, and zearalenone

    Fumonisins, trichothecenes, and zearalenone are the most important mycotoxins produced by Fusarium, a producer of a wide range of toxic compounds.

    Tricothecenes are related compounds and the more important are grouped into type A or type B.

    Type A are more toxic than type B. However, the latter are more common and therefore more relevant to food safety.

    T-2 toxinwas probably the cause of “alimentary toxic aleukia” which affected thousands of people in Siberia during the Second World War.

    It is responsible for haemorrhagic disease in animals and is associated with the formation of oral lesions and neurotoxic effects in poultry.

    The most significant effect of this and other trichothecenes is the immunosuppressive activity, which is probably linked to the inhibitory effect on the biosynthesis of macromolecules (e.g., DNA, proteins).

    Fumonisins, trichothecenes, and zearalenone

    Another important Fusarium toxin is zearalenone (ZEA), which has oestrogenic properties.

    Mycotoxines

    Control

    The control and detection of mycotoxins is a continuous process in commodity production.

     production, storage, transportation and processing chain

    Analysis is normally by chromatography. Initially, thin layer chromatographic(TLC) methods were employed

    However, this has been superseded, in many cases, by high performance liquid chromatography (HPLC). Gas chromatography is often used for Fusarium mycotoxins.

    The use of immunoaffinity columns for analysis of most of the main mycotoxins has greatly improved analysis in terms of quantification, purification and convenience.

    Immunological test kits such as ELISA are available but they are not as accurate as the chromatography-based methods.

    TLC is optimal for the detection of previously unknown “new” compounds because of the more universal detection methods employed

    Control: Good agricultural practice (GAP)

    In the case of peanuts, it is known that the formation of aflatoxins in the plant takes place when ambient temperatures of 25 to 32 °C occur simultaneously with low humidity in the soil.

    Therefore, it is possible to control

    the biosynthesis of aflatoxins in peanuts by controlled irrigation at critical periods of the day.

    After harvest, (aw) and temperature.

    Others are cleaning, insect control, use of antifungal agents and maintaining integrity of the seed coat.

     These parameters, if not kept at the desired levels, may lead to the growth of fungi and the accumulation of mycotoxins in stored crops

    Harvested grain, coffee beans, fruits, and oilseeds crops should be dried immediately.

    The final safe moisture depends on crop and climatic conditions where stored.

     Corn which is contaminated with A. flavus and subjected to increased moisture by 18 % for 4-6 h can increase aflatoxin levels

    Early harvesting of corn followed by drying may avoid increased aflatoxin contamination Grain needs to be dried to 15% or less before storing and toxin production.

     Insects and rodents need to be controlled as they create conditions suitable for fungal growth,

    Air treatment in storage facilities may prevent growth and contamination, e.g., propionic acid, mixtures of propionic and acetic acid, or ozon.

    from granulated products, such as cereals, bean or others, since contaminated kernels have distinctive characteristics.

    Removal of mycotoxins after harvesting

    Damaged kernels may exhibit differences in colour, density, shape or size.

    These contaminated kernels have a lower density, as does contaminated corn, and thus removal is possible by flotation and density sorting.

    These procedures are reported to remove more than 90% of aflatoxins

    Aflatoxins and OTA are rather stable when exposed to dry heat and less stable when exposed to humid heat

    Boiling rice at normal pressure reduces aflatoxins up to 50 %. Increasing the temperature increases the level of aflatoxin transformation: a pressure-cooking can degrade aflatoxins by 70 %.

    Removal during processing

    Frying can reduce aflatoxins by 60 % when oil temperature is at 150 °C for 20 minutes.

     OTA is partially removed from coffee beans during roasting.

    Degradation of OTA to a maximum of 90 % is possible, depending to the conditions of operation while roasting (e.g. temperature usually between 200 and 250 °C and resident time from 5 to 20 minutes).

    Aflatoxins present in edible oil after its extraction from seeds are mainly dispersed

    Water is a good solvent for OTA in certain food matrixes, such as coffee:so brewing coffee is the perfect way of extracting OTA from the coffee grains to the cup!

    aflatoxin M1 usually has a higher concentration in cheese than in milk

    However, aflatoxins are generally insoluble in water and so may also dissolve more readily in the lipid rich cheese fraction.

    Enzymes and microorganisms are used frequently in food processing and may transform mycotoxins into other compounds with less or unknown toxicity This is the case with proteases.

    They can hydrolyze thepeptide bond of OTA yielding phenylalanine and the much less toxic ochratoxin alpha.

    S. cerevisiae transforms patulin into other compounds during alcohol production in cider production.

     Patulin is also degraded by (a) sulphur dioxide,and (b) sulphur containing proteins.

    This approach should be considered as a method for reducing patulin in other commodities.

     


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