Grain storage techniques: The biodeterioration of grain and the risk of mycotoxins

Biodeterioration

The condition of stored grain is determined (Lacey, 1988) by a complex interaction between the grain, the macro- and micro-environment and a variety of organisms (including microorganisms, insects, mites, rodents and birds) which may attack it.

Grain provides an abundant source of nutrients, and the natural consequence of the type of stable ecosystem described above will normally be spoilage (biodeterioration) of the grain, caused by the organisms.

The extent of contamination by moulds is largely determined by the temperature of the grain and the availability of water and oxygen. Moulds can grow over a wide range of temperatures, from below freezing to temperatures in excess of 50°C. In general, for a given substrate, the rate of mould growth will decrease with decreasing temperature and water availability. Moulds utilise intergranular water vapour, the concentration of which is determined by the state of the equilibrium between free water within the grain (the grain moisture content) and water in the vapour phase immediately surrounding the granular particle. The intergranular water concentration is described either in terms of the equilibrium relative humidity (ERM, %) or water activity (aw). The latter describes the ratio of the vapour pressure of water in the grain to that of pure water at the same temperature and pressure, while the ERH is equivalent to the water activity expressed as a percentage. For a given moisture content, different grains afford a variety of water activities and, consequently, support differing rates and type of mould growth. Typical water activities which are necessary for mould growth range from 0.70 to 0.90.

The interaction between grain temperature and moisture content also affects the extent of mould colonisation. The passage of water from the grain into the vapour phase is encouraged by an increase in temperature. Consequently, for a given moisture content, the water activity, and the propensity for mould growth, will increase with temperature. Maize, for example, can be relatively safely stored for one year at a moisture level of 15 per cent and a temperature of 15°C. However, the same maize stored at 30°C will be substantially damaged by moulds within three months.

Insects and mites (arthropods) can, of course, make a significant contribution towards the biodeterioration of grain, through the physical damage and nutrient losses caused by their activity. They are also important, however, because of their complex interaction with moulds and, consequently, their influence on mould colonisation.

In general, grain is not infested by insects below a temperature of 17°C whereas mite infestations can occur between 3 and 30°C and above 12 per cent moisture content. The metabolic activity of insects and mites causes an increase in both the moisture content and temperature of the infested grain. Arthropods also act as carriers of mould spores and their faecal material can be utilised as a food source by moulds. Furthermore, moulds can provide food for insects and mites but, in some cases, may may also act as pathogens.

Another important factor that can affect mould growth is the proportion of broken kernels in a consignment of grain. Broken kernels, caused by general handling and/or insect damage, are predisposed to mould invasion of the exposed endosperm. It has been estimated, for example, that increasing the proportion of broken grains by five per cent will reduce the storage-life of that consignment by approximately one order of magnitude; that is from, say, 150 to 15 days.

Mould growth is also regulated by the proportions of oxygen, nitrogen and carbon dioxide in the intergranular atmosphere. Many moulds will grow at very low oxygen concentrations; a halving of linear growth, for example, will only be achieved if the oxygen content is reduced to less than 0.14 per cent. Interactions between the gases and the prevailing water activity also influence mould growth.

Moulds and mycotoxins 

The interactions described above, within granular ecosystems, will support the growth of a succession of micro-organisms as the nutrient availability and microenvironment changes with time. In the field, grains are predominantly contaminated by those moulds requiring high water activities (at least 0.88 aw) for growth, whereas stored grains will support moulds which grow at lower moisture levels. The rate of mould growth is also determined by the ability of the micro-organism to compete with other species. Some species, including those of Aspergillus, Penicillium and Fusarium, can occur both in the field and in storage.

Secondary metabolites are those compounds, produced by living organisms, which are not essential for growth. Some secondary metabolites produced by moulds are highly toxic to animals, humans and plants. These so-called ‘mycotoxins’ have been extensively studied since 1961, when a group of highly toxic Aspergillus flavus toxins – the aflatoxins – were isolated from a consignment of groundnut meal which had been imported into the UK (Coker, 1979).

Any activity which disturbs the stability of an ecosystem will increase the production of secondary metabolites, including mycotoxins. Such activities include the widespread use of fertilizers and pesticides, high yielding plant varieties and the cultivation of a limited number of plant species with restricted genetic variation. The normal practices of harvesting, drying and storage also, of course, significantly disturb the ecosystems of grains established before harvest.

The major mycotoxin-producing moulds include (Miller, 1991) certain Aspergillus, Fusarium and Penicillium species. Toxigenic (mycotoxin-producing) Aspergillus moulds can occur both before and after harvest, whereas Fusarium and Penicillium moulds occur predominantly before and after harvest respectively. In general, Aspergillus is associated with the tropics and Penicillium with temperate climates, whereas Fusarium moulds occur world wide. However, because of the complexity and variety of ecosystems supporting mould growth in grains, the nature and extent of the worldwide occurrence of moulds and mycotoxins cannot, as yet, be confidently defined. About 300 mycotoxins have been reported, produced by a wide variety of moulds. A few of the major moulds and mycotoxins are listed in Table 2.1 and discussed in the following sections of this Chapter.

Table 2.1. The major moulds and mycotoxins.

The significance of mycotoxins 

Mycotoxins have been implicated in a range of human and/or animal diseases and occur in a variety of grains. The ingestion of mycotoxins can produce both acute (short-term) and chronic (medium/long-term) toxicities ranging from death to chronic interferences with the function of the central nervous, cardiovascular and pulmonary systems, and of the alimentary tract. Some mycotoxins are carcinogenic, mutagenic, teratogenic and immunosuppressive. Aflatoxin B.

for example, is one of the most potent hepatocarcinogens known.

The mycotoxins have attracted worldwide attention, over the past 30 years, firstly because of their perceived impact on human health, secondly because of the economic losses accruing from condemned foods/feeds and decreased animal productivity and, thirdly, because of the serious impact of mycotoxin contamination on internationally traded commodities. It is estimated, for example, that the cost of managing the mycotoxin problem on the North American continent is approximately $5 billion.

The Aflatoxins

The aflatoxin-producing moulds Aspergillus flavus and A. parasiticus occur widely, on inadequately dried food and feed grains, in sub-tropical and tropical climates throughout the world. Pre-harvest mould growth, and aflatoxin production, is encouraged by insect damage, mechanical damage, drought stress and excessive rainfall. The aflatoxins may occur, both before and after harvest, on virtually any food or feed which supports fungal growth, including cereals, oilseeds and edible nuts. Maize, groundnuts, cottonseed, oil-palm kernels and copra are particularly associated with the occurrence of the aflatoxins. The very substantial international trade in these commodities serves to amplify the worldwide nature of the aflatoxin problem.

The ingestion of aflatoxin B1-contaminated animal feed, by dairy cattle, can result in the presence of aflatoxin M1 (Figure 2. 1e) – a metabolite of aflatoxin B1 – in milk. This is an issue of considerable importance to public health, given the frequent consumption of milk and dairy products by infants.

Aflatoxin B. has been confirmed as a highly potent human carcinogen, whereas the carcinogenicity of the aflatoxins G1 (Figure 2.1c) and M, has been confirmed only in experimental animals.

The acute toxicity of the aflatoxins has been demonstrated in both animals and man. The outbreak of ‘Turkey X’ disease in the UK, in the early 1960s, was associated with the death of thousands of turkeys, ducklings and other domestic animals which had received a diet containing aflatoxin-contaminated groundnut meal. Many human fatalities occurred (Anon, 1993(a)) in India, in 1974, when unseasonal rains and a scarcity of food prompted the consumption of heavily aflatoxin-contaminated maize. Acute aflatoxicosis, also caused by the consumption of contaminated maize, caused fatalities in Kenya in 1982.

The chronic effects, caused by the consumption of low dietary levels (parts per billion) of the aflatoxins, on the health and productivity of domestic animals are well established. Reduced weight gain has been reported (Anon, 1989), for example, in cattle, pigs and poultry; reduced milk yield in cows; and reduced feed conversion in pigs and poultry. Low levels of aflatoxin have been associated with an increased susceptibility to disease in poultry, pigs and cattle. Vaccine failures have also been reported. If similar immunosuppressive effects are manifested in humans, it is possible that the aflatoxins (and other mycotoxins) could be significantly enhancing the incidence of human disease in developing countries.

The Trichothecenes

The trichothecenes comprise a large group of mycotoxins, produced by a variety of Fusarium moulds. The current discussion will be limited to the two trichothecenes – T-2 toxin and deoxynivalenol – which occur naturally, in significant quantities, in cereal grains.

(i) T-2 toxin 

F. sporotrichioides, the major producer of T-2 toxin, occurs mainly in temperate to cold areas and is associated with cereals which have been allowed to overwinter in the field (Anon, 1993(b)). T-2 toxin has been implicated in two outbreaks of acute human mycotoxicoses. The first occurred in Siberia (in the former USSR), during the Second World War, producing a disease known as ‘alimentary toxic aleukia’ (ATA). Thousands of people, who had been forced to eat grain which had overwintered in the field, were affected and entire villages were eliminated. The symptoms of ATA included fever, vomiting, acute inflammation of the alimentary tract, anaemia, circulatory failure and convulsions. Trichothecene poisoning also occurred in Kashmir, India, in 1987 and was attributed to the consumption of bread made from mouldy flour. The major symptom was abdominal pain together with inflammation of the throat, diarrhoca, bloody stools and vomiting. T-2 toxin was isolated from the flour together with other trichothecenes, namely deoxynivalenol, nivalenol and deoxynivalenol monoacetate (Figures 2.2b, 2.2c and 2.2d respectively).

T-2 toxin has been implicated with the occurrence of haemorrhagic toxicoses (mouldy maize toxicoses) in farm animals. Oral lesions, severe oedema of the body cavity, neurotoxic effects and, finally, death have been reported in poultry, after the ingestion of feed contaminated with T-2.

The most significant effect of T-2 toxin, and other trichothecenes, may be the immunosuppressive activity, which has been clearly demonstrated in experimental animals. The effect of T-2 toxin on the immune system is probably linked to the inhibitory effect of this toxin on the biosynthesis of macromolecules.

There is limited evidence that T-2 toxin may be carcinogenic in animals.

(ii) Deoxynivalenol (Figure 2.2b)

F. graminearum occurs worldwide and is the most important producer of deoxynivalenol (DON) (Anon, 1993(c)). The outbreaks of emetic (and feed refusal) syndromes in farm animals, produced by the presence of DON in their diets, has resulted in the trivial name, vomitoxin, being attributed to this mycotoxin.

DON is probably the most widely distributed Fusarium mycotoxin occurring in a variety of cereals, particularly maize and wheat. As stated above, DON has been implicated in a human mycotoxicosis, in India, in combination with T-2 toxin and other trichothecenes. Other outbreaks of acute human mycotoxicoses, caused by the ingestion of DON and involving large numbers of people, have occurred in rural Japan and China. The Chinese outbreak, in 1984-85, resulted from the ingestion of mouldy maize and wheat. The onset of symptoms occurred within five to thirty minutes and included nausea, vomiting, abdominal pain, diarrhoea, dizziness and headache. Another F. graminearum toxin, zearalenone (see below), was also isolated from the mouldy foodstuff.

The immunosuppressive effect, of those concentrations of DON which are naturally ocurring, has been reported. There is inadequate evidence in humans and experimental animals, however, for the carcinogenicity of DON. DON is not transferred into milk, meat or eggs.

Zearalenone 

F. graminearum is also the most important producer of zearalenone, a widely-occurring mycotoxin which is responsible for many outbreaks of oestrogenic syndromes amongst farm animals (Maracas, 1991).

The occurrence of zearalenone in maize has been responsible for outbreaks of hyperestrogenism in animals, particularly pigs, characterised by vulvar and mammary swelling, uterine hypertrophy and infertility.

As described above, zearalenone was isolated from mouldy cereals involved in an outbreak of acute human mycotoxicosis in China.

There is limited evidence in experimental animals, and inadequate evidence in humans, for the carcinogenicity of zearalenone. It is not transmitted from feed to milk to any significant extent.

The Fumonisins 

The fumonisins are a group of mycotoxins which have been characterised comparatively recently (Anon, 1993(d). They are produced by F. moniliforme which occurs worldwide and is one of the most prevalent fungi associated with maize.

To date, only the fumonisins FB1 and FB2 appear to be toxicologically significant. The occurrence of FB1 in cereals, primarily maize, has been associated with serious outbreaks of leukoencephalomalacia (LEM) in horses and pulmonary oedema in pigs. LEM is characterised by liquefactive necrotic lesions of the white matter of the cerebral hemispheres and has been reported in many countries, including the USA, Argentina, Brazil, Egypt, South Africa and China. FB1 is also toxic to the central nervous system, liver, pancreas, kidney and lung in a number of animal species. FB2 is hepatotoxic in rats.

The incidence of F. moniliforme in domestically-produced maize has been correlated with human oesophageal cancer rates in the Transkei, southern Africa and in China. The levels of fumonisins in domestically-produced maize have been reported as similar to those levels which produced LEM and hepatotoxicity in animals.

Currently, there is inadequate evidence for the confirmation of the carcinogenicity of the fumonisins in humans. There is limited evidence, in animals, for the carcinogenicity of FB1 but inadequate evidence for the carcinogenicity of FB2. Data are not available for the transmission of these toxins into milk, meat and eggs.

Ochratoxin A 

Ochratoxin A is produced (Pitt and Leistner, 1991) by only one species of Penicillium, P. verrucosum, probably the major producer of this mycotoxin in cooler regions. Amongst the aspergilli, Aspergillus ochraceus is the main source of ochratoxin A.

Ochratoxin A has been mainly reported in wheat and barley growing areas in temperate zones of the northern hemisphere. It does, however, occur in other commodities including maize, rice, peas, beans and cowpeas; developing country origins of ochratoxin A include Brazil, Chile, Egypt, Senegal, Tunisia, India and Indonesia.

A correlation between human exposure to Ochratoxin endemic’nephropathy (a fatal, chronic renal disease occurring in limited areas of Bulgaria, the former Yugoslavia and Romania) has been suggested. A causative link, however, has yet to be confirmed.

Ochratoxin A produces renal toxicity, nephropathy and immunosuppression in several animal species.

Although there is currently inadequate evidence in humans for the carcinogenicity of ochratoxin A, there is sufficient evidence in experimental animals. Ochratoxin A has been found in significant quantities in pig meat, as a result of its transfer from feeding stuffs.

The interaction of mycotoxins 

The complex ecology of mould growth and mycotoxin production can produce mixtures of mycotoxins in food and feed grains, particularly in cereals. The co-occurrence of mycotoxins can arise through a single mould producing more than one toxin and simultaneous contamination by two or more moulds, from the same or different species.

The co-occurrence of the Fusarium graminearum toxins deoxynivalenol and zearalenone with the F. moniliforme toxins fumonisin B1 and B2, for example, has been reported (Miller, 1991) in southern Africa. Other naturally occurring combinations of Fusarium mycotoxins include T-2/diacet-oxyscirpenol (DAS)  

deoxynivalenol/DAS and DAS/fusarenone (Figure 2.6b). Naturally occurring combinations of mycotoxins produced by more than one genus include aflatoxins/trichothecenes (Argentina), aflatoxins/zearalenone (Brazil, Indonesia), aflatoxins/ Ochratoxin A and aflatoxins/cyclopiazonic acid (Figure 2.6c)/zearalenone (Indonesia), afla-toxins/fumonisins (USA). Given the worldwide distribution of the Fusariummoulds, the presence of combinations of Fusarium mycotoxins and aflatoxins in food and feeds of developing country origin should be expected.

The co-occurrence of mycotoxins can affect both the level of mycotoxin production and the toxicology of the contaminated grain. The presence of trichothecenes may increase the production of aflatoxin in stored grain, for example, whereas some naturally occurring combinations of Fusarium toxins are synergistic in laboratory animals. To date, little is known about this particularly important area of mycotoxicology. The significance of mycotoxins in human disease will become more clearly defined through the continued identification of biomarkers, present in blood and/or urine, which reflect the levels of recent dietary exposure to mycotoxins. Aflatoxin, covalently bound to albumin in peripheral blood, and the urinary aflatoxin B1-guanine adduct have both been used, for example, to monitor aflatoxin ingestion.

Studies using the aflatoxin-albumin adduct have demonstrated the significantly higher exposure that occurs in Gambia, Kenya and the Guangxi region of China, compared with Thailand and Europe. In Europe, the levels of biomarker were below the detection limit.

The control of mycotoxins 

Since the occurrence of mycotoxins is a consequence of biodeterioration, it follows that the mycotoxin problem is best addressed by controlling those agents – temperature, moisture and pests – which encourage spoilage.

The pre-harvest control of the agents of biodeterioration is somewhat compromised by Man’s inability to control the climate! Both insufficient and excessive rainfall during critical phases of crop development can, for example, lead to mould contamination and mycotoxin production. The very substantial economic losses attributed to mycotoxins, on the North American continent, clearly illustrates the difficulties associated with the prevention of contamination, even in wealthy, developed nations.

Considerable effort has been expended on the development of crop strains which are resistant to mould growth and/or mycotoxin production. Breeding programmes have focused, for example, on the development of Aspergillus/aflatoxin resistant varieties of maize and groundnuts, with limited success. It has been suggested that wheat has three types of resistance to Fusarium graminearum; resistance to the initial infection, resistance to the spread of the infection and resistance to mycotoxin (deoxynivalenol) production. Attempts to exploit the resistance to mycotoxin production (through either the inhibition of synthesis or chemical degradation) may hold the most potential because of the limited number of genes which control this process.

The post-harvest handling of grains does, however, present many more opportunities for controlling mycotoxin production. Although many small farmers will not have access to artificial drying equipment, the importance of the utilisation of effective drying, and storage regimes cannot be overemphasised, and is covered extensively in later chapters. Drying to moisture levels which will ensure safe storage in tropical climates is especially important when grains are shipped from temperate to tropical climates.

However, despite the best efforts of the agricultural community, mycotoxins will continue to be present in a wide range of foods and feeds. Consequently, strategies are required for the removal of mycotoxins from grains. Currently, two approaches are utilised; namely, the identification and segregation of contaminated material and, secondly, the destruction (detoxification) of the mycotoxin(s).

The Segregation of Contaminated Grains

In the first instance, the identification and segregation of contaminated consigments is pursued through the implementation of quality control procedures by exporters, importers, processors and regulators. The consignment is accepted or rejected on the basis of the analysis of representative samples of the food or feed. Acceptable levels of mycotoxin contamination are specified by individual customers, commercial agreements and regulators. Currently, over 50 countries now regulate against the aflatoxins; 5 parts per billion (µg/kg) is the most common maximum acceptable level. Aflatoxin M1 in dairy products is regulated in at least 14 countries, the tolerances for infant diets being 0.05-0.Sppb milk. Regulations exist for other mycotoxins including, for example, zearalenone (1mg/kg in grains; the former USSR), T-2 toxin (0.1mg/kg in grains; the former USSR) and ochratoxin A (150ppb food, 100-1000ppb feed; numerous countries). Guidelines, advisory levels and ‘official tolerance levels’ for deoxynivalenol also exist in some countries. The guideline in Canada, for example, refers to 2mg/kg in uncleaned soft wheat, 1mg/kg in infant foods and 1.2mg/kg in uncleaned staple foods calculated on the basis of flour or bran. In the USA, 4mg/kg is advised for wheat and wheat products used as animal feeds.

The mycotoxin content of grains can be further reduced during processing. Automatic colour sorting, often in combination with manual sorting, is widely used to segregate kernels of abnormal appearance (which are considered more likely to contain aflatoxin) during the processing of edible grade groundnuts. Mycotoxins can also be concentrated in various fractions produced during the milling process. Zearalenone and deoxynivalenol, for example, are reportedly concentrated in the bran fraction during the milling of cereals. It can be argued, however, that all fractions will contain mycotoxins if the original grain is heavily contaminated. Ochratoxin A appears to be reasonably stable to most food processes. In general, the stability of mycotoxins during processing will depend upon a number of factors including grain type, level of contamination, moisture content, temperature and other processing agents.

A further segregation process involves the removal of aflatoxin, from animal feeds, after ingestion. Here, mycotoxin binding agents – hydrated sodium calcium aluminosilicate, zeolite, bentonite, kaolin, spent canola oil bleaching clays – included in the diet formulation, reportedly remove aflatoxin, by adsorption from the gut.

The Detoxification of Mycotoxins

Ammonia, as both an anhydrous vapour and an aqueous solution, is the detoxification reagent which has attracted (Park et al, 1988) the widest interest and which has been exploited commercially, by the feed industry, for the destruction of aflatoxin. Commercial ammonia detoxification (ammoniation) facilities exist in the USA, Senegal, France and the UK, primarily for the treatment of groundnut cake and meal. In the USA, cottonseed products are treated in Arizona and California whilst maize is ammoniated in Georgia, Alabama and North Carolina. Commercial ammoniation involves the treatment of the feed, with ammonia, at elevated temperatures and pressures over a period of approximately 30 minutes. Onfarm procedures, as practiced with cottonseed in Arizona, involve spraying with aqueous ammonia followed by storage at ambient temperature, for approximately two weeks, in large silage bags.

The nature of the reaction products of the ammoniation of aflatoxin is still poorly understood. However, many studies have been performed, on both isolated ammoniation reaction products and treated feedingstuffs, in an attempt to define the toxicological implications of ammoniation. Very extensive feeding trials have been performed with a variety of animals including trout, rats, poultry, pigs and beef and dairy cattle. The effect of diets containing ammoniated feed has been determined by monitoring animal growth and organ weights together with haematological, histopathological and biochemical parameters. The results of these studies, combined with the practical experience of commercial detoxification processes, strongly indicate that the ammonia detoxification of aflatoxin is a safe process. However, the formal approval of the ammoniation process by the USA Food and Drug Administration is still awaited.

Commercial processes have not been developed for the detoxification mycotoxins.

Sampling and analysis 

The control of the mycotoxin problem comprises (a) the identification of the nature and extent of the problem (by the implementation of surveillance studies), (b) the introduction of improved handling procedures, which address the identified problems, and (c) the regular monitoring of foods and feeds as part of a quality control programme.

The operation of both surveillance studies and quality control programmes requires efficient sampling and analysis methods.

Since the distribution of aflatoxins (and, presumably, other mycotoxins) in grains is highly skewed, it is important that great care is taken to collect a representative sample (Coker and Jones, 1988). There is still considerable debate as to the appropriate size of such samples. In general, the sample size should increase with increasing particle size; samples of whole groundnuts, maize and rice, for example, should be of the order of 20, 10 and 5kg respectively. Samples of oilseed cake and meal should be approximately 10kg in weight. For whole grains, each sample should be composed of about 100 incremental samples, collected sytematically from throughout the batch, whereas samples of cake and meal require approximately 50 increments. It is important to remember that the collection of samples from the surface of a large, mature stack of grains will only reflect the quality of the outer layers. The mycotoxin content of the grain in the interior of the stack can only be monitored during the break-down of the stack. Needless to say, an incorrectly collected sample will invalidate the final analysis result.

The sampling of grain shipments, normally involving tens of thousands of tonnes of material, poses a particularly difficult sampling problem. Representative samples should be collected from carefully defined 500 tonne batches, using the methods described above. Potential sampling points include weighing towers, conveyor belts, and trucks and barges receiving the discharged material. The sampling of fast moving grain is a hazardous operation; automatic, on-line sampling equipment should be used wherever possible.

The reduction of the sample, for analysis, should also be performed so as to ensure the representative nature of the laboratory sample. It is imperative that the complete sample is comminuted prior to subdivision. Ideally, the comminution and subdivision of whole grains should be performed simultaneously, using a subsampling mill. Alternatively, the comminuted sample should be subdivided using a mechanical riffle. Manual coning and quartering procedures should only be used as a last resort.

Equipment available for the collection of representative samples is discussed in detail in Chapter 3.

High performance liquid chromatography (HPLC) has been used for the analysis of a wide range of mycotoxins including the aflatoxins, ochratoxin A, zearalenone, deoxynivalenol (DON) and the fumonisins. To date, high performance thin layer chromatography (HPTLC) has been applied mainly to the aflatoxins whereas gas liquid chromatography (GLC) has been utilised for the quantification of DON, T-2 toxin and zearalenone. Enzyme-linked immunosorbent assays (ELISA) have also been applied to many mycotoxins including the aflatoxins, ochratoxin A, deoxynivalenol, T-2 toxin and zearalenone. Despite the utilisation of sophisticated, expensive HPLC, HPTLC, GLC and ELISA procedures, agreement between laboratories is invariably poor, when identical samples are analysed (Coker, 1984)!

Quality control programmes require simple, rapid, efficient analysis methods which can be handled by relatively unskilled operators (Coker, 1991). Recently developed rapid methods include those that utilise immunochemistry technology or selective adsorption agents. A rapid ELISA method for estimating aflatoxin in groundnuts, cottonseed, maize, rice and mixed feeds has been subjected to a collaborative study and recommended for First Action Approval by the Association of Official Analytical Chemists (AOAC). Solid phase ELISA kits have been developed for the aflatoxins, ochratoxin A, zearalenone and T-2 toxin in a variety of commodities. An ‘immunodot’ cup test, where the antibody is immobilised on a disk in the centre of a small plastic cup, has been approved by the AOAC as an Official First Action screen for aflatoxin in groundnuts, maize and cottonseed. Card tests have also been developed where the antibody is immobilised within a small indentation on a card similar in size to a credit card. Such tests have been developed for the aflatoxins, ochratoxin A, T-2 toxin and zearalenone in maize. The reported analysis (extraction, filtration and estimation) time for solid phase ELISA kits is 5-10 minutes. ELISA kits, however, are relatively expensive and suffer reduced shelf-lives at elevated temperatures.

Minicolumns (small glass columns) containing selective adsorption agents have been developed for aflatoxin/zearalenone (single test) and deoxynivalenol.

There is an urgent need for simple, robust, low-cost analysis methods, for the major mycotoxins, which can be routinely used in developing country laboratories.

Conclusions 

The mycotoxins described in this chapter, as symptoms of biodeterioration, are acutely toxic, carcinogenic, immunosuppressive and oestrogenic; and have been the cause of serious human and/or animal diseases. The potential immunosuppressive role of mycotoxins in the aetiology of human disease is an especially important issue which requires further careful study. Every effort must be made to minimise the occurrence of mycotoxins in food and feed grains.

Undoubtedly, the implementation of improved handling and quality control procedures will have a significant effect on the incidence of mycotoxins in important foods and feeds throughout the world.

Edited by D.L. Proctor, FAO Consultant

FAO AGRICULTURAL SERVICES BULLETIN No. 109

GASCA – GROUP FOR ASSISTANCE ON SYSTEMS RELATINGTO GRAIN AFTER HARVEST