Chemical Food Contaminants (Mycotoxins) – III

Mycotoxins

Mycotoxins are a group of naturally occurring chemicals produced by certain molds/fungi. There are many such compounds, but only a few of them are regularly found in food and animal feedstuffs such as grains and seeds. They can grow on a variety of different crops and foodstuffs including cereals, nuts, spices, dried fruits, apple juice and coffee, often under warm and humid conditions, where presence of mycotoxins in grains and other staple foods and feedstuffs has serious implications for human and animal health. Since they are produced by fungi, mycotoxins are associated with diseased or moldy crops, although the visible mold contamination can be superficial. Many countries have enacted regulations stipulating maximum amounts of mycotoxins permissible in food and feedstuffs. Most developed countries will not permit the import of commodities containing amounts of mycotoxins above specified limits, where Mycotoxins have implications for trade between nations. Thus prevention of fungal invasion of commodities is by far the most effective method of avoiding mycotoxin problems, where integrated commodity management program focusing on the maintenance of commodity quality from the field to the consumer will be one of the best alternatives.

Aflatoxins

Aflatoxins were discovered over 30 years ago which have been subject to a great deal of research. They are potent human carcinogens and interfere with the functioning of the immune system. Among livestock, they are particularly toxic to chickens. In 1993, the International Agency for Research on Cancer (IARC) assessed and classified naturally occurring mixtures of aflatoxins as class 1 human carcinogens where Aflatoxins B1, B2, G1, and G2 have been found to occur in commodities and have been detected in human sera. IARC has concluded that aflatoxin B1 is a class 1 human carcinogen including residues of aflatoxin B and/or its metabolite, aflatoxin M, can occur in animal products, and milk. Aflatoxin M, is also found in human milk if the mother consumes food containing aflatoxin B1. IARC has given aflatoxin M, a lower carcinogenicity rating than aflatoxin B1.

Types of Mycotoxins

There are five groups of mycotoxins, which occur quite often in foods from both groups are: deoxynivalenol/nivalenol, zearalenone, ochratoxin, fumonisins and aflatoxins. T-2 toxin is also found in a variety of grains but its occurrence, to date, is less frequent than the preceding five mycotoxins. The fungi that produce mycotoxins in food fall broadly into two groups: those that invade before harvest, commonly called field fungi, and those that occur only after harvest, called storage fungi.

There are three types of toxicogenic field fungi:

Plant pathogens such as F. graminearum (deoxynivalenol, nivalenol);

Fungi that grow on senescent or stressed plants, such as F. moniliforme (fumonisin) and sometimes A. flavus (aflatoxin); and

Fungi that initially colonise in the plant before harvest and predispose the commodity to mycotoxin contamination after harvest, such as P. verrucosum (ochratoxin) and A. flavus (aflatoxin).

Mycotoxins in Grains and Seeds

Mycotoxin	Commodity	Fungal Source(s)	Effects of Ingestion
deoxynivalenol/ nivalenol	wheat, maize, barley reported from	Fusarium graminearum	Human toxicoses India, China, Japan, and Korea. Toxic to animals, especially pigs
		Fusarium crookwellense
		Fusarium culmorum
zearalenone	maize, wheat	F. graminearum	Identified by the International Agency for Research on Cancer (IARC) as a possible human carcinogen. Affects reproductive system in female pigs
		F. culmorum
		F. crookwellense
ochratoxin A	barley, wheat, and many other commodities	Aspergillus ochraceus	Suspected by IARC as human carcinogen. Carcinogenic in laboratory animals and pigs
		Penicillium verrucosum
fumonisin B1	maize	Fusarium moniliforme plus several less common species	Suspected by IARC as human carcinogen. Toxic to pigs and poultry. Cause of equine eucoencephalomalacia (ELEM), a fatal disease of horses
aflatoxin B1, B2	maize, peanuts, and many other commodities	Aspergillus flavus	Aflatoxin B1, and naturally occurring mixtures of aflatoxins, identified as potent human carcinogens by IARC. Adverse effects in various animals, especially chickens
aflatoxin B1, B2, G1, G2	maize, peanuts	Aspergillus parasiticus

Ecology

In the case contamination of mycotoxin contamination, there is a more or less well defined association between the fungus and its plant host. Aspergillus and Fusarium species are likely to be the most significant mycotoxin producing field fungi found in tropical developing countries, i.e., moldy, damaged peanuts. High levels of aflatoxins in this commodity have frequently been found in parts of South-East Asia due to the result of poor handling and storage practices. Fusarium kernel rot is one of the most important ear diseases of maize in hot growing areas which is associated with warm, dry years and/or insect damage. There is a strong relationship between insect damage and fusarium kernel rot. It has been found during field survey work, for example, that the incidence of the European corn borer increased F. moniliforme disease and fumonisin concentrations. Maize infected with fusarium kernel rot, one of the most important ear diseases of maize in hot growing areas because temperature stress of the growing plant is important, because studies of fumonisin occurrence in maize hybrids grown across the U.S. Corn Belt, Europe and Africa, indicate that hybrids grown outside their range of temperature adaptation have higher fumonisin concentrations.

After harvest, when grains or seeds have become moribund or dormant as a result of drying, associations between fungi and plants disappear, and physical factors dictate whether or not members of the other group - the storage fungi - will grow and/or produce mycotoxins. The primary factors influencing fungal growth in stored food products are the moisture content (more precisely, the water activity) and the temperature of the commodity. As a generally accepted fact about tropics; the temperature is almost always suitable for storage fungi, so it is the water activity that becomes the prime determinant of fungal invasion and growth in stored grains.

Food Safety and Mycotoxins

The mycotoxins of most concern from a food safety perspective include the aflatoxins (B1, B2, G1, G2 and M1), ochratoxin A, patulin and toxins produced by Fusarium moulds, including fumonisins (B1, B2 and B3), trichothecenes (principally nivalenol, deoxynivalenol, T-2 and HT-2 toxin) and zearalenone. Mycotoxins can cause a variety of adverse health effects in humans. Aflatoxins, including aflatoxin B1 are the most toxic and have been shown to be genotoxic i.e. can damage DNA and cause cancer in animal species. There is also evidence that they can cause liver cancer in humans. Other mycotoxins have a range of other health effects including kidney damage, gastrointestinal disturbances, reproductive disorders or suppression of the immune system. For most mycotoxins, a tolerable daily intake (TDI) has been established, which estimates the quantity of mycotoxin which someone can be exposed to daily over a lifetime without it posing a significant risk to health.

It is clear that exposure to aflatoxins is hazardous to human health where, most countries have regulations governing the allowable concentrations of aflatoxin in food and feed.  Aflatoxin B, the most toxic of the aflatoxins, causes a variety of adverse effects in different domestic animals. Effects on chickens include liver damage, impaired productivity and reproductive efficiency, decreased egg production in hens, inferior egg-shell quality, inferior carcass quality and, most important from a human perspective, increased susceptibility to disease.

Exposure Methods

When people are around toxic mold they are usually exposed to airborne mycotoxins by breathing them in. These mycotoxins end up in the lungs and cause breathing problems and other severe symptoms. Mycotoxins in the air can also enter through a person's eyes. Trichothecene mycotoxins can be absorbed through the skin as well. Another way mycotoxins get into a person's body is by the person eating food with mycotoxins in it. This can happen if toxic mold has been growing on crops. Many mycotoxins, for example trichothecene, remain toxic even after being cooked. This is one reason why mycotoxins are a big problem in agriculture. A binding agent is used on crops such as grain after harvesting to remove mycotoxins.

Symptoms

In 2004, there were 125 people died after eating maize contaminated with aflatoxin mycotoxins in Kenya, and there are many cases of pets dying from eating pet food with mycotoxins in it as well. The effects of some food-borne mycotoxins are acute, symptoms of severe illness appearing very quickly. Other mycotoxins occurring in food have longer term chronic or cumulative effects on health, including the induction of cancers and immune deficiency. Information about food-borne mycotoxins is far from complete, but enough is known to identify them as a serious problem in many parts of the world, causing significant economic losses.

Risks of Contamination

The food-borne mycotoxins likely to be of greatest significance for human health in tropical developing countries are the fumonisins and aflatoxins. Fumonisins were discovered as recently as 1988, thus there is little information on their toxicology. To date, there is sufficient evidence in experimental animals for the carcinogenicity of cultures of Fusarium moniliforme that contain significant amounts of fumonisins; and there is limited evidence in experimental animals for the carcinogenicity of fumonisin B1. F. moniliforme growing in maize may produce fumonisin B1, a suspected human carcinogen. Also, fumonisin B1 is toxic to pigs and poultry, and is the cause of equine leucoencephalomalacia (ELEM), a fatal disease of horses. Fumonisins have been found as a very common contaminant of maize-based food and feed in Africa, China, France, Indonesia, Italy, the Philippines, South America, Thailand, and the USA. Strains of F. moniliforme from maize from all over the world, including Africa, Argentina, Brazil, France, Indonesia, Italy, the Philippines, Poland, Thailand, and the USA, produce fumonisins. At present, strains of F. moniliforme isolated from sorghum are considered to be poor producers of fumonisins.

Prevention of Mycotoxin Contamination – Common Control Measures

Drying – Fungi cannot grow (or mycotoxins be produced) in properly dried foods, where efficient drying of commodities and maintenance of the dry state is an effective control measure against fungal growth and mycotoxin production. To reduce or prevent production of most mycotoxins, drying should take place soon after harvest and as rapidly as feasible. The critical water content for safe storage corresponds to a water activity (a_w) of about 0.7. Maintenance of foods below 0.7 a_w is an effective technique used throughout the world for controlling fungal spoilage and mycotoxin production in foods. Problems in maintaining an adequately low a_w often occur in the tropics, where high ambient humidities make control of commodity moisture difficult. Where grain is held in bags, systems that employ careful drying and subsequent storage in moisture-proof plastic sheeting may overcome this problem. 

Proper rapid drying is the best means to avoid fungal growth and mycotoxin production in grain after harvest. At times when sun drying is not possible or unreliable some form of mechanical drying may be necessary. While it is possible to control fungal growth in stored commodities by controlled atmospheres or use of preservatives or natural inhibitors, such techniques are almost always more expensive than effective drying, and are rarely feasible in developing countries.

Minimize Grain Damage – Damaged grain is more prone to fungal invasion and thereby mycotoxin contamination where it is important to avoid damage before and during drying, and storage. Drying of maize on the cob, before shelling, is a very good practice. Insects are a major cause of damage where field insect pests and some storage species damage grain on the head and promote fungal growth in the moist environment of the ripening grain. In storage, many insect species attack grain, and the moisture that can accumulate from their activities provides ideal conditions for the fungi. To avoid moisture and mold problems, it is essential that numbers of insects in stored grain be kept to a minimum. Such problems are intensified if the grain lacks adequate ventilation, particularly if metal containers are used.

Ensure Proper storage Conditions – While keeping commodities dry during storage in tropical areas can be difficult, the importance of dry storage cannot be overemphasized. On a small scale, polyethylene bags are effective; on a large scale, safe storage requires well-designed structures with floors and walls impermeable to moisture. Maintenance of the water activity of the stored commodity below 0.7 is crucial. In tropical areas, outdoor humidity is usually fall well below 70% on sunny days, where appropriately timed ventilation, fan-forced if necessary, will greatly assist the maintenance of the commodity at below 0.7 a_w. Ideally, all large-scale storage areas should be equipped with instruments for measuring humidity, so that air appropriate for ventilation can be selected. Sealed storage under modified atmospheres for insect control is also very effective for controlling fungal growth, provided the grain is adequately dried before storage, and provided diurnal temperature fluctuations within the storage are minimized. 

If commodities must be stored before adequate drying, it should be only for short periods of no more than three days. Use of sealed storage or modified atmospheres will prolong this safe period, but such procedures are relatively expensive and gaslight conditions are essential. A proven system of storage management is needed, with mycotoxin considerations an integral part of it. A range of decision-support systems is becoming available covering the varying levels of sophistication and scale involved.

Methods of Eliminating Mycotoxins

Mycotoxins aren't actually alive like mold spores, where removal or destruction is really means breaking down of mycotoxins and their toxicity which will no longer dangerous to humans. Bleach with 5% sodium hypochlorite disintegrates trichothecene mycotoxins as well as other mycotoxins including aflatoxin. It takes fire at 500⁰F (260⁰C) for half an hour or fire at 900⁰F (482⁰C) for 10 minutes to destroy trichothecene mycotoxins. In addition, ozone is supposed to oxidize most or all mycotoxins, but the level of ozone you need to oxidize mycotoxins is not safe for humans. Therefore, if you use an ozone-generator there must be no one in the building. HEPA air filters are not effective at removing mycotoxins where activated carbon filters can remove mycotoxins from the air. Mycotoxins are eventually broken down and lose their toxicity after some time, but some types of mycotoxins may take several years though, for example trichothecene mycotoxins which are among the most resilient.

Detection of mycotoxins

Mycotoxins occur, and exert their toxic effects, in extremely small quantities in foodstuffs where identification and quantitative assessment generally require sophisticated sampling, sample preparation, extraction, and analytical techniques. Under practical storage conditions, the aim should be to monitor for the occurrence of fungi and if fungi cannot be detected, then there is unlikely to be any mycotoxin contamination. The presence of fungi indicates the potential for mycotoxin production, and the need to consider the fate of the batch of commodity affected. While there are means of decontaminating affected commodities, all are relatively expensive, and their efficiency is still a matter of debate. The need for simple, rapid, and efficient mycotoxin analysis methods that can be handled by relatively unskilled operators has been recognize and some progress made towards developing them. The U.S. Federal Grain Inspection Service (FGIS) has evaluated eight commercially available, rapid tests for aflatoxin in maize. FGIS-approved kits include rapid ELISA, immune-affinity cartridge, solid-phase ELISA, and selective adsorbent mini-column procedures. There remains a need for efficient, cost-effective sampling and analysis methods that can be used in developing country laboratories. Various governments have set regulatory limits for mycotoxins in food and animal foodstuffs presented for sale or import. For aflatoxin, guidelines range from 4 to 50 µg/kg (parts per billion). Regulatory limits for fumonisin are under consideration. For all mycotoxins, it is likely that, as analytical techniques and knowledge of the toxins improve, allowable limits will fall.