Introduction to Mycotoxins

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Introduction to Mycotoxins

http://www.mycotoxins.org/

Introduction

The name mycotoxin combines the Greek word for fungus 'mykes' and

the Latin word 'toxicum' meaning poison. There are numerous

varieties of fungi ranging from those commonly seen growing in woods

and fields to microscopic species that can infest growing or stored

crops. Most of these species live on dead organic matter that they

help to decompose while many can cause diseases in plants. Moulds

can be of great benefit to man as nutritious foods or as the source

of antibiotics and other useful chemicals. On the adverse side,

direct ingestion of a 'toxic' fungus, e.g. following

misidentification, is a well-known cause of illness or death.

The term 'mycotoxin' is usually reserved for the toxic chemical

products formed by a few fungal species that readily colonise crops

in the field or after harvest and thus pose a potential threat to

human and animal health through the ingestion of food products

prepared from these commodities. 'St 's fire' was one of the

earliest recognised diseases caused by mycotoxins in Europe well

known by the end of the first millennium. This was the result of

eating rye contaminated with ergot alkaloids produced by the mould

Claviceps purpurea. The epileptic fits and excruciating burning

sensation experienced led many pilgrims to the shrine of St

in France in hope of a cure.

More recently the death of 100 000 turkey poults and other poultry

in the UK just before Christmas in 1960 was eventually traced to a

toxic contaminant later called aflatoxin that was present in

groundnut meal forming part of their diet. This incident illustrated

the potential threat posed by mycotoxins and ushered in the modern

era of mycotoxin studies.

Fungi and the formation of mycotoxins

Each mycotoxin is produced by one or more very specific fungal

species. In some cases one species can form more than one mycotoxin.

For example the aflatoxins can be formed by Aspergillus flavus,

Aspergillus parasiticus and limited other Aspergilli, while

ochratoxin A is considered to be mainly the product of A. ochraceus

in tropical regions and P. verrucosum in temperature areas. However,

the presence of a recognised toxin-producing fungus does not

automatically imply the presence of the associated toxin as many

factors are involved in its formation. Conversely, the absence of

any visible mould does not guarantee freedom from toxins as the

mould may have already died out while leaving the toxin intact.

The products affected

Any crop that is stored for more than a few days is a target for

mould growth and mycotoxin formation. Mycotoxins can occur both in

tropical areas and in temperate regions of the world, depending on

the species of fungi. Major food commodities affected are cereals,

nuts, dried fruit, coffee, cocoa, spices, oil seeds, dried peas and

beans and fruit, particularly apples. Mycotoxins may also found in

beer and wine resulting from the use of contaminated barley, other

cereals and grapes in their production. Mycotoxins also enter the

human food chain via meat or other animal products such as eggs,

milk and cheese as the result of livestock eating contaminated feed.

Why mycotoxins are important

Mycotoxins cause a diverse range of toxic effects because their

chemical structures are very different from each other. Acute

effects require that high amounts are present when eaten so that

such incidents are usually restricted to the less developed parts of

world where resources for control are limited, or to livestock.

Chronic effects are of concern for the long-term health of the human

population and are important when present in much lower amounts.

Some of the most common mycotoxins are carcinogenic, genotoxic, or

may target the kidney, liver or immune system.

National and International Organisations are constantly evaluating

the risk that such mycotoxins pose to man. For some mycotoxins this

has resulted in statutory or guideline maximum permissible limits.

Many countries now have legal limits for aflatoxins that are the

most widespread and toxic mycotoxins, although these values are by

no means uniform.

Stability and persistence

Most mycotoxins are chemically stable so they tend to survive

storage and processing even when cooked to quite high temperatures

such as those reached during baking bread or producing breakfast

cereals. This makes it important to avoid the conditions that lead

to mycotoxin formation as far as possible. This is difficult to

achieve for the growing crop that is subject to the prevailing

climate and conditions. Once dried adequately at harvest, further

growth of moulds and mycotoxin formation should be prevented during

storage and transport although this is frequently not achieved in

practice.

Sampling and analysis

Fungi tend to develop in isolated pockets in stored commodities.

This results in a very uneven distribution within a consignment of

the mould as it grows and any associated mycotoxin. Hence it is

vital that a strategy is developed to ensure that a sample taken for

analysis is truly representative of the whole consignment. Most

mycotoxins are toxic in very low concentrations so this requires

sensitive and reliable methods for their detection. Sampling and

analysis taken together represents an extremely demanding challenge

for the analyst. Failure to achieve a satisfactory performance can

lead to unacceptable consignments being accepted or satisfactory

loads being unnecessarily rejected. Cargoes may be valued at many

thousands of pounds and disputes about the analytical results can be

extremely costly especially if this results in the reputation of the

trader or retailer being unfairly tarnished.

Control

The difficulty of removing a mycotoxin once formed means that the

best method of control is prevention. However, many measures have

been studied to reduce the effects of moulds. Examples are the

development of mould resistant species, alternative methods of soil

cultivation, drying and storage techniques and so on. Recently, a

HACCP like approach has been evaluated as a means to identify the

Critical Control Points and provide a management tool to reduce or

eliminate the hazard.

FURTHER INFORMATION

General information on important mycotoxins is provided in a set of

fact sheets. Detailed information is given in further fact sheets

covering occurrence, toxicity, prevention, sampling and analytical

methods, quality assurance and processing.

Acknowledgement: The establishment of this network was funded by the

European Commission, Quality of Life and Management of Living

Resources Programme (QoL), Key Action 1 (KA1) on Food, Nutrition and

Health, QLK1-CT-2000-01248.

E-mail: eman@...