FACT SHEET - www.micotoxinas.com.br
Richard Lawley, Leatherhead Food International, Randalls Road, Leatherhead, Surrey KT22 7RY, England
Naturally Occurring Deoxynivalenol and Related Compounds
Deoxynivalenol also known as DON or vomitoxin is one of about 150 related compounds known as the trichothecenes that are formed by a number of species of Fusarium and some other fungi. Because deoxynivalenol is toxic and often found in foodstuffs, sometimes in high concentrations, it has recently been of concern to International Organisations and Government Food Agencies.
It is nearly always formed before harvest when crops are invaded by certain species of Fusarium such as F. graminearum and F. culmorum. These two species are important plant pathogens and cause Fusarium heat blight in wheat and Gibberella ear rot in maize. Deoxynivalenol is thermally stable so once formed it is likely to persist through storage and the food chain.
Chemical and Physical Properties
Deoxynivalenol is one of the more polar trichothecenes with a molecular weight of 296.32. It contains one primary and two secondary hydroxyl groups and is soluble in water and polar solvents such as methanol and acetonitrile. Unlike many of the other trichothecenes the molecule contains a conjugated carbonyl system and this results in some UV absorbance that assists its detection by TLC or HPLC methods. In contaminated cereals 3- and 15-acetyl deoxynivalenol can co-occur in significant amounts with deoxynivalenol. It is chemically very stable.
Toxicity and Importance
It is often difficult to relate experimental results of studies of the toxicology of deoxynivalenol with what occurs under real life situations because invariably there are other related trichothecenes present. However, acute toxicity of deoxynivalenol is characterised by vomiting particularly in pigs, feed refusal, weight loss and diarrhoea. Acute intoxication may produce necrosis in various tissues such as the gastrointestinal tract, bone marrow and lymphoid tissues.
Subchronic oral exposure in experimental animals, pigs, mice and rats may also lead to reduced feed intake and slowed weight gain and changes in some blood parameters including serum immunoglobulins. Studies suggest that deoxynivalenol may have effects on the immune system. There are no indications of carcinogenic, mutagenic or teratogenic effects.
A study reporting human food poisoning by infected wheat containing deoxynivalenol in India showed a range of symptoms including abdominal pains, dizziness, headache, throat irritation, nausea, vomiting, diarrhoea and blood in the stool. However, it is highly likely that other related compounds were also present.
The European Commissions Scientific Committee on Food considered the general toxicity and immunotoxicity to be the critical effects. At a meeting in February 2001 JECFA (The Joint FAO/WHO Expert Committee on Food Additives set a provisional TDI of 1 µg/kg b.w. after considering the data available.
Products affected and Natural Occurrence
The main commodities affected are cereals and deoxynivalenol is a frequent contaminant of grains such as wheat, buckwheat, barley, oats, triticale, rye, maize, sorghum and rice. Using methods with sensitivities of about 5 µg/kg it is possibly to show that more than 50% of samples may be contaminated when the appropriate species of Fusarium infect growing cereals. Concentrations have been reported up to as high as 9 mg/kg in barley and 6 mg/kg in wheat. Because it is a stable compound it has also been detected in a range of processed cereal products including breakfast cereals, bread, noodles, infant foods, malt and beer. The presence of deoxynivalenol in barley causes the problem of gushing in beer. However, the transfer of deoxynivalenol from animal feed to meat and other animal products appears to be extremely small. The formation of deoxynivalenol in growing crops is dependent on climate and will thus vary between geographical region and year so that regular monitoring is desirable.
Sampling and Analysis
Representative sampling is important as it is with other mycotoxins in cereals. Its distribution in bulk grain has been poorly studied and sampling plans derived for other mycotoxins such as aflatoxin and ochratoxin A should be followed.
Deoxynivalenol can be extracted from cereals using aqueous solvent mixtures such as methanol and water or acetonitrile and water. Because deoxynivalenol has some uv absorbence it is possible to detect it using TLC or HPLC although the sensitivity of these techniques is relatively poor. ELISA based methods have been developed and commercial kits are available. Such methods should be thoroughly evaluated before use. However, the most sensitive method is GC usually in tandem with a mass spectrometer. The advantage of this is that other related compounds can be determined simultaneously and high sensitivity attained. The disadvantages are that deoxynivalenol is non-volatile must be derivatised to form a stable derivative suitable for analysis and that expensive equipment and skilled operators are required for its operation.
Stability and Persistence
Deoxynivalenol is thermally stable so it is difficult to eliminate from grain once formed. During the milling process of wheat it fractionates so that the higher levels concentrate in the outer bran layers and the concentration in white flour is lower than in the original grain. Because deoxynivalenol is water soluble a significant proportion can be removed by washing grain but commercially this represents an additional stage and an effluent problem. Enzymic reactions have been shown both to reduce and increase levels of deoxynivalenol. This is most likely due to the inter-conversion of related molecules or precursors.
Legislation and Control
Until recently few countries notably Austria, Canada and the USA have had any statutory or guideline limits for deoxynivalenol. However, in the 1990s concerns were raised about the detection in the Netherlands of high concentrations of deoxynivalenol in food products eaten by children. Thus in 2000 the EC advised action be taken on deoxynivalenol and proposed action levels (but not regulatory limits) of 500 ppb for cereal products as consumed and other products at the retail stage, 750 ppb for flour used as raw material in food products and 750 ppb as a monitoring level for raw cereals