Aflatoxin research on grain in Asia - its problems and possible solutions
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T.D. Cardona, S.G. Ilangantileke and A. Noomhorm
Cereals, especially maize, are the major source of carbohydrates in Asia and are important as export products in some Asian countries. As export crops, grain quality has been critically monitored to meet international standards. Mycotoxin development in many stored cereal grains has constantly hampered the availability of good quality grains in Asian countries. Of the major problems, the fungi Aspergillus flavus and Aspergillus parasiticus have been identified as the quality deterrent producing aflatoxin contaminated grain when stored. In the last decade, aflatoxin levels on produce was found to exceed an acceptable level limit of 50 ppb stipulated in most export specifications.
Aflatoxin contamination has affected maize and peanuts in Thailand arid India and also in coconut in the Philippines, Sri Lanka and other Pacific countries. Aflatoxicoses both in humans and animals and liver cancer among humans have been more prevalent in areas where maize constitutes a major part of the diet. Because of these findings, research has been focused on identifying causal factors and formulating effective preventive and control measures against aflatoxin. Many private and government organisations have embarked on aflatoxin research. However, many problems are associated with the actual research activities concerning aflatoxin.
This study reviews aflatoxin research on grain in the Asian region. In the review, constraints for aflatoxin research are identified and are research methodologies such as sampling techniques; financial restrictions to procure sophisticated equipment and chemicals for precise aflatoxin analysis; scarcity of highly trained and experienced personnel for aflatoxin research; absence of facilities for safe aflatoxin research; unawareness among farmers about aflatoxin hazards; stress factors when the crops are still in the field due to inadequate infrastructure for production; policies on aflatoxin contaminated produce and other possible problems towards the reduction of aflatoxin contaminated produce.
This paper, in addition, attempts to suggest solutions which hopefully, will minimize the constraints in aflatoxin research, based on those identified.
Mycotoxins are toxic secondary metabolises produced by fungi. For centuries, these mycotoxins have been associated with quality degradation of many agricultural products which cause considerable changes in texture, flavor and colon Although many toxic mould metabolises have been isolated through laboratory cultures from agricultural products, only seven have been found to have possible significant occurrence in naturally contaminated foods and feeds. These are aflatoxin, zearalenone, ochratoxin A, citrinin, trichothecenes patulin, penicillic acid and the ergot alkaloids. Among these mycotoxins, aflatoxins have gained considerable attention because they are most toxic and potent carcinogen even in small quantities (FAO, 1979, Mirocha and Christensen, 1982, and Campos, 1987). In 1981, the maximum limit for aflatoxin in food (aflatoxin B. or the sum of aflatoxins B1, B2, G1 and G2 vary from zero to 50 parts per billion (ppb) (Van Egmond, 1987 and Jewers 1987).
Aflatoxins are a family of related bisfuranocoumarin compounds produced by fungi Aspergillus flavus and Aspergillus parasiticus. The term aflatoxin was derived from Aspergillus (A-) falvus (-fla-) and toxin. It has been reported that out of the known strains of Aspergillus flavus and Aspergillus parasiticus, only about one-half produce toxins. There are 14 known aflatoxins but most of these are metabolises formed endogenously in animals administered by one major toxins, i.e., aflatoxin B. (AFB1) aflatoxin B2 (AFB2), aflatoxin G. (AFG1) and aflatoxin G2 (AFG2) (B= blue fluorescence and G = green fluorescence). Aspergillus flavus was produces AFB1 and AFB2 whilst Aspergillus parasiticus produces the four mayor toxins (Lillehoj, 1986).
Aflatoxins are often isolated in cereals, cereal products, groundnuts and beans. They have also been detected in cotton seeds, copra, nuts, cassava, eggs and cheese. This is alarming in Asia since cereals and groundnuts are the major items in the diet. The situation may be aggravated by the fact that there is a relatively high incidence of aflatoxin in warmer areas which is true in most Asian countries. In addition, harvesting seasons in Asian countries usually fall on the onset, of the wet season. During this period, sun drying may not be possible which is the usual method employed by most of the farmers. Thus, grain enters the storage system at high moisture content. Aflatoxin contamination occurs when the crops could not be dried within 48 hours (FAO, 1979, llangantileke, 1987, Campos, 1987, Sanchis et al., 1988 and Luxsanakoses, 1989). Furthermore, with the green house effect or global warming, alteration of the climatic conditions in most Asian countries have been observed.
Over the past decade aflatoxicoses both in humans and animals and liver cancer among humans have been reported in India (FAO, 1979 and Bilgrami and Sinha, 1986), Thailand (RIO, 1988, Angsubhakorn, 1989 and Boon-long et al.), Philippines (Ilag, 1984 and RIO, 1988), Taiwan (Angsubhakorn, 1989 and Pitt, 1989a) and Indonesia (Machmud, 1987). Aflatoxicosis caused acute liver damage, liver cirrhosis, induction of tumours, attack on the central nervous system, skin disorders and hormonal effects (Pitt, 1989a). Epidemiological studies have indicated a relationship between aflatoxin intake and incidence of liver cancer in several developing countries. Pitt (1989b) reported that there is high incidence of human liver cancer in Central Africa and parts of Southeast Asia. Studies have shown a correlation between the logarithm of aflatoxin intake and the occurrence of primary liver cancer. Aside from health hazards, aflatoxins cause economic and nutritional losses. Because of these findings, several government as well as private institutions have been engaged in aflatoxin research with the aim of identifying the factors enhancing its contamination and formulating effective strategies for its prevention and control. However, several problems have been associated with aflatoxin research.
This paper envisions to review the aflatoxin research on grain in Asia and subsequently identify problems that have been encountered. Consequently, recommendations leading to the solutions on the identified problems shall be made.
REVIEW OF LITERATURE
The toxic effects of aflatoxins have been described as early as 1913 but the toxin was not isolated and the subject was forgotten. Aflatoxicosis in swine had been reported in 1940 in Georgia, USA. The death of the swine was traced as a result of feeding mouldy maize. Similar incidence happened in 1950 at Alabama (FAO, 1979 and Schaible, 1979). In 1959, a singular event occurred in Britain specifically in East Anglia where thousands of turkey poults died over a very short period of time. it was quickly demonstrated that these birds died from a poison present in the pelleted feed which formed a major part of the diet. The major raw materials used were protein rich plant products such as groundnut meal imported from tropical and subtropical countries. Examination of the incriminated groundnut meal revealed the presence of mould mycelium and thin layer chromatography showed the presence of several new compounds which fluresce intensively under ultraviolet light. The mould was shown to be Aspergillus falvus and its highly toxic metabolises were called aflatoxins. The acute toxicity of aflatoxin is shown in Table 1. Aflatoxins have been reported as a potent carcinogens and there have been many cases of aflatoxicosis in humans. These findings triggered off an intensive international research effort resulting in a massive literature on this single group of mycotoxins. In early 1960's the term mycotoxin and aflatoxin were synonymous (Smith and Moss, 1985). Araullo et al. (1976) and Lillehoj (1986) considered the outbreak of unknown disease in England as the first evidence of aflatoxin poisoning.
Table 1. Acute toxicity of aflatoxin B1 expressed as a single oral dose LD50
|Species||LD50 mg kg (-1) bodyweight|
|Duckling (11 day old)||0.43|
|Dog||0.50 - 1.00|
|Sheep||1.00 - 2.00|
|Guinea pig||140 - 2.00|
|Rat (male)||5.50 - 7.20|
a/ The LD50 is the dose that will cause the death of 50 percent of a statistically significant population. It is usually obtained by extrapolation from dose response experiments.
Aflatoxins are important because some are extremely toxic to many kinds of animals; 10 ppb AFB1 consumed regularly by rats may eventually result in fatal liver cancer and in somewhat larger amounts-a few hundred ppb-aflatoxin cause a great variety of ill effects in wild and domestic animals. An aflatoxin contamination level of 20 ppb is permitted in feed grains and in feeds in the U.S.A. but in foods intended for human consumption the tolerance is zero. However, these guidelines were then revised. North Carolina agricultural officials reported that maize containing up to 200 ppb could be fed to heifers (older than 6 months), calves and bulls and to non-lactating brood cows. Maize containing aflatoxin higher than 20 ppb should not be fed to lactating animals, used as any starter ration or feed to poultry. All other animals could be fed with maize containing aflatoxin levels up to 100 ppb. For human consumption, a level, below 20 ppb is enforced (Mirocha and Christensen 1982 and Pitt, 1989b).
The natural incidence of aflatoxins in food and feed is influenced by climate. Practically, all tropical countries encounter the problem of aflatoxin contamination. Unfortunately, the climatic conditions in Asian countries are very favorable for aflatoxin producing fungi (Bilgrami and Sinha, 1986). This situation is aggravated in places where harvest season coincides with the wet months since most farmers rely on sundrying to reduce the moisture content of freshly harveshly harvested crops (llangantileke, 1987). Aflatoxin contamination has been frequently encountered in cereals especially maize, rice, groundnuts and other oily products. Aflatoxicoses both in humans and animals as well as primary liver cancer have been reported in many Asian countries where the above mentioned products have been a constituent of the diet (Campos, 1987 and Pitt, 1989a).
In India, maize is grown in 16 states in India which has a total production of 6.1 million tons as cited by FAO (1979) a large part of which is consumed as human food. Aflatoxin has become a problem since droughts and floods occur alternately in various states during the growing and harvesting seasons. Although, there was no systematic survey of maize in India, it was reported that aflatoxin contaminated maize caused toxicosis in two western states in 1974.
India is the second largest producer of rice in the world. It was reported that aflatoxin has been a problem in rice. However, only limited information is available. In one study conducted in Magalore, Karnatake, 6% of all sample gathered revealed the presence of aflatoxin. Reddy et al. (1986) reported that the incidence of Aspergillus flavus colonies in broken rice ranges from 11 to 12%.
Aftatoxin was also detected in groundnuts. In a study conducted in Andhra Pradesh in 1965, aflatoxin levels were in the range of 1,000 and 5,000 ppb in 12% of 743 in-shell and 141 groundnut cake samples. Aflatoxin levels were highest in samples of the rainy season crop. The 1965-1967 survey in Gujarat, Andhar Pradesh and Madras revealed that 10-40% of grounPradesh and Madras revealed that 10-40% of groundnuts and 82% of groundnut cakes conducted in the western coast in 1967 68 revealed that nearly 50% of 500 groundnut samples collected had aflatoxin B1 at levels between 100 to 250 ppb. In 1976, 50% of the groundnut cake samples collected mostly in Madhya Pradesh region were positive for aflatoxin (FAO, 1979 and Reddy et al., 1986).
One of the earliest report on aflatoxicosis in animals was in Andhra Pradesh on 24 Murrah buffaloes. The symptoms were a loss of appetite, diarrhea and dullness. Histopathological studies revealed centrilobular hepatic cell necrosis, bile duct proliferation and central vein occlusion. Aflatoxicoses were also reported in Karnataka which resulted in the mortality of 58 crossbred castles, abortion in pregnant buffaloes and death of 2219 chicks. Large-scale mortality of ducklings in government farms and swine at breeding farm were reported in Kerala. In Kulu Valley, more than 4000 rabbits died due to the consumption of aflatoxincontaminated pellets. Large-scale mortality of dogs were also reported in Western India 1974 due to feeding on food remnants containing high levels of aflatoxin (Bilgrami and Sinha, 1986).
The effect of aflatoxins on primates was studied in the National Institute of Nutrition in Hyderabad on monkeys. The quantity of aflatoxin M, excreted in the urine of albino rats, guinea pigs and monkeys was studied at the Central Food And Technological Research Institute in Mysore. Also, the effects of aflatoxins on humans were studied. Circumstantial evidence suggests the involvement of the toxin in human disease and deaths. Indian childhood cirrhosis (ICC) a serious disorder of the liver in children was reported to be caused by aflatoxins through mothers' milk and foods such as parboiled rice and unrefined peanut oil. Malnourished children who had consumed aflatoxincontaminated protein flour developed hepatic lesions similar to that of ICC. Urine and liver extracts from ICC children were examined and subsequently, the presence of aflatoxins was confirmed in about 7% of the urine samples of 332 children. The scientists of the National Institute of Nutrition in Hyderabad, on the other hand, undertook detailed investigations on the outbreak of acute hepatitis in the tribal belts in Western Indian where 100 people died. Death caused by consumption of maize grains heavily contaminated with aflatoxins up to 1560 ppb (Bilgrami and Sinha, 1986, Pitt, 1989a and Pitt, 1989b).
In Thailand, aflatoxin has been a great problem in maize. Recently, Thai maize has lowered its foreign market ability due to a high incidence of aflatoxin (Tangthirasunan, 1989 and Yoshlyama, 1989). This problem is very significant since Thailand ranked fourth as a maize exporter in the world. The major buyers of Thai maize were Hongkong, Japan, Taiwan and Singapore. The aflatoxin levels for these countries are: Japan 10 ppb (AFB1) Hongkong 20 ppb (AFB1 + B2 + G1 + G2 + M1 + M2 + P1 + Aflatoxicol); Taiwan (ROC) 50 ppb (AFB1) and Singapore 0. Thai maize frequently exceeds these levels in the rainy season. Because of this, maize is traded at $10$20 per ton below than that of maize from other sources. The annual cost to Thailand of the aflatoxin and related quality problems, is not less than US$50 million. (Buangsuwon, 1986, Van Egmond, 1987a and RIO, 1988).
The main cause of initial aflatoxin contamination in maize is during temporary farm storage of undried ears for one to six weeks before the crop is sold. In a survey made in 1967-1969, the average level in the contaminated samples was found to be 2,730 ppb. In 1985, a mean aflatoxin level of 74 ppb with a range of 3 to 299 ppb was reported (FAO, 1979 and Buangsuwon, 1986).
The incidence of aflatoxin contamination in rice in the market was determined by a survey conducted in 1967-1969. Aflatoxin was detected in raw rice in the range of 20 to 98 ppb in 2% samples out of a total of 364 samples. In another survey conducted in 3 locations, Singburi was reported to have, 3% of the samples of prepared rice contaminated with aflatoxin at levels up to 600 ppb; in Ratburi, 10% were contaminated with levels up to 180 ppb and in Songkhla, 1% contained aflatoxin at concentrations up to 71 ppb. Aflatoxin was found to be highest in the rainy season and lowest in the hot season (FAO 1979).
Aflatoxin is also a problem in peanut. In a survey conducted in 1967-1969,49% had an average aflatoxin level of 1,530 ppb. The highest level observed was 12,300 ppb out of 219 samples collected from 100 towns and villages (FAO, 1979 and Campos, 1987). Buangsuwon (1986) reported that a higher incidence of aflatoxin contamination was found in shelled peanuts, especially in samples of damaged kernels where 9 out 15 samples had aflatoxin contamination ranging from 0 to 350 ppb and in samples of damaged kernels in which all 20 samples had readings of 15 to 1350 ppb.
Aflatoxin has been linked to outbreaks of Raye's syndrome which was an epidemic in Northeast Thailand affecting children up to the age of adolescence. It was reported that aflatoxin was found in 22 out of 23 children affected by the disease. Similar symptoms to those of Reye's syndrome were obtained by feeding large quantities of aflatoxin to Macaque monkeys (RIO, 1988) and Angsubhakorn, 1989).
The incidence of primary liver cancer was found to be correlated with the consumption of aflatoxin contaminated foods. One case of acute aflatoxicosts was reported causing the death of a child consuming contaminated rice. The child was said to have consumed steamed rice contaminated with aflatoxin for two days approximately in the range of 6 mg daily prior to the total illness (FAO, 1979).
The mycotoxin research in the Philippines has been concentrated solely on aflatoxin since it is a highly potent poison affecting several animal species and is a common contaminant of many important agricultural produce including maize, peanut and copra. Other mycotoxins have not so far been reported to occur in the country although the Food and Nutrition Research Institute has reported the presence of a small amount of ochratoxin and zearalenone in maize. A survey conducted in 1972, revealed that the aflatoxin content of various agricultural crops and their byproducts were in large quantity. Malze samples were usually laden with the toxin. Some samples showed no visible sign of Aspergillus falvus but contained aflatoxin while others had Aspergillus falvus but no toxin. It was reported that maize grown in Visayas and Mindanao had more toxin than those grown in Northern Luzon. Palay, soybean and millet however, were noted to be poor substrates for aflatoxin production (Ilag, 1984).
The risk potential from aflatoxin in the Philippines is alarming because of the prevailing high temperature and relative humidity which favors fungal growth. In addition, heavy rain coincides with the peak harvest months of staple cereals, particularly maize. As a consequence, handling of high moisture grain is commonly encountered and subsequently leads to aflatoxin formation (Garcia and flag, 1986).
Studies on rice indicated that under current handling practices, palay or rough rice contain low levels of aflatoxin or none at all. However, milled or brown rice when inoculated with toxicogenic strains of Aspergillus falvus and Aspergillus parasiticus, yieladed very high levels of the toxin. Aflatoxin B1 in brown rice was found to be concentrated on the bran layers whereas the polished rice contained no toxin or only traces of aflatoxin (Ilag, 1984).
A study by the Food and Nutrition Research Institute on the aflatoxin content of various food items in the country revealed that groundnuts under natural condition contain high level of aflatoxin (Ilag, 1984). Lagunda (1989) reported that aflatoxin build-up in the 4 day windrowed and mechanically stripped pods was observed at 15 days of storage. The aflatoxin level increased from an initial value of 0.432 ppb up to 108.559 ppb after 45 days of storage. He concluded that 4 day curing and mechanical stripping is not recommended due to the build-up of aflatoxin.
A study by Jayme et al. (1982) showed that primary liver cancer (PLC) ranks first among malignancies that reach autopsy. It was concluded that there is a strong positive association between the ingestion of increasing levels of aflatoxin and the rising risk of developing primary liver cancer. This effect is synergistically aggravated by alcohol consumption.
There has been no report on aflatoxin incidence on maize in Taiwan. As cited earlier, Taiwan is one of the major importers of maize in Asian countries. Since the aflatoxin level is strictly stipulated in trade, the level of toxin is within an acceptable limit of 50 ppb.
A study published in 1968 reported that no aflatoxin was detected in rice collected from markets in Taiwan. However, aflatoxin was found in one of the samples of mouldy rice that was collected from families in which 25 people became ill and 3 children died of unknown cause. Of the five samples analyzed one contained 200 ppb of aflatoxin B1 (FAO, 1979).
Aflatoxin in groundnut was also studied in 1966. Samples taken from 3 out of the 8 oil mills revealed the presence of aflatoxin B. in the range of 40 to 430 ppb. Groundnut cake samples collected from 4 to 12 oil mills were positive for aflatoxin and contained 80 to 290 ppb of AFB1 (FAO, 1979).
In Indonesia, there is no report on the incidence of aflatoxin in maize as of 1977. However, Widiastuti et al. (1988) cited that cyclopiazonic acid has been found to be accompanied by other mycotoxins especially aflatoxins from samples collected from Bogor poultry feedmill. FAO (1979) cited that aflatoxin in trace amounts was detected in rice handled by the distributors but was negative at the storage facilities where rice bought from the farmers were stored. Analysis of four samples suspected to be contaminated showed the presence of aflatoxin G1 in one at a concentration of 15 ppb.
Groundnut is an important crop in Indonesia. About 10% of the crop was exported as reported by FAO in 1979. A comparison of aflatoxin contamination of groundnut samples collected from 3 points in 1970 showed that higher level of aflatoxin in retail groundnuts was attributed to inadequate protection from wetting during rainy weather. Aflatoxin levels were found in groundnut press cake taken in West Java. It was reported that higher levels of aflatoxin was found in groundnuts used for making groundnut oil than those destined for the retail market. This happened because lower grades of groundnuts were used for oil extraction. Machmud (1988) reported that about 60-80% of marketable groundnuts were contaminated with aflatoxin at levels from 40-4100 ppb and retail groundnuts were highly contaminated.
PROBLEMS ON AFLATOXIN AND AFLATOXIN RESEARCH
Over a decade of aflatoxin research on grain in Asian countries and other tropical and subtropical countries, have caused researchers to encounter several problems. These problems encompass the physical, analytical, socio-political, pathological and mycological aspects. Some of these problems or constraints are enumerated as follows:
1. Sampling, Subsampling and Sample Handling
Blanc (1987) commented that no sampling method for aflatoxin tests in groundnut kernels and cakes is considered totally reliable. This is not only true in groundnut but also in other agricultural commodities particularly cereals. Hongsuwong (1989) stated that sampling error is usually the largest contributor to the total error. This would have a great impact considering that one positive aflatoxin analysis on a single shipment on any commodity could lead to the rejection of the entire lot.
Sampling for aflatoxin determination has been a critical factor in aflatoxin research since aflatoxin is extremely variable in nature. Huff (1980) reported that concentration of aflatoxin in artificially inoculated maize was not even homogeneous. Lee et al. (1980) said that aflatoxin is very heterogeneous and that kernels containing a high level of aflatoxin were often adjacent to aflatoxin negative kernels. To date, no absolute quantity of sample has been recommended for a single aflatoxin prone commodity. Most researchers suggested that 5-10 kg representative sample should be taken from a sample lot for analysis (Buangsuwon, 1986).
Jones (1972) commented that it is difficult to lay down strict rules on sampling. Various trade bodies also have their own sampling procedure. Van Egmond (1987) reported that only limited information is available about the use of sampling plans.
RIO (1988), pointed out that sampling and more specifically sample division using whole maize kernels rather then ground kernels, is seen as the major source of error in official inspection and for quality control testing.
FAO (1982) reported that sampling of lots of food or feed selected for examination is one of the most difficult and often most costly aspects of conducting a survey. The size of the sample to be taken as representative of a particular lot of food depends on the type of commodity to be examined.
2. Lack of Funds and Other Resources
In all research activities, adequate funding is a dire need to accomplish the objectives satisfactorily. The government of any country where mycotoxin problems have been identified should provide sufficient funds for research as well as extension activities. Bhat (1987) reported that the funding pattern for mycotoxin prevention and control strategies is minimal. The political commitment of most governments is generally directed for increased production of agricultural commodities and less priority is provided for postharvest techonolgy aspects especially on mycotoxin control programs. Moreover, Blanc (1987) and Campos (1987) pointed out that research and extension programmes on aflatoxin could not be implemented due to the lack of funds.
Considerable resources are necessary on aflatoxin studies specially on a large scale program. Aflatoxin is not only a problem among agriculturists and food scientists but also to veterinarians, biologists, microbiologists, and other related fields. Hence, a multidiscriplinary approach to overcome the constraints might be feasible since aflatoxin itself is not only a postharvest problem. These programmes need adequate resources in terms of personnel, energy source, capital investment and analytical and technical facilities (FAO, 1977, Garcia and flag, 1986 and Campos, 1987).
Laboratories in most Asian countries are not as sophisticated as those in developed countries. Technical apparatus such as Thin Layer Chromatography (TLC), High Performance Liquid Chromatograph (HPLC) are necessary for the accurate detection of mycotoxin contamination. In Asia, TLC is the most common apparatus for aflatoxin detection but this equipment is not as accurate as the HPLC.
Recently, a semi-quantitative approach to detect aflatoxin have been developed for faster and is less expensive than the quantitative method. May and Baker of U.K. has developed an aflatest kit using a minicolumn. This method is faster and useful for silo operators as tested in Thailand. Another is the method developed by the Plant Pathology section of the Department of Agriculture in Thailand. It employs a minicolumn principle to extract toxin that could be prepared easily in the laboratory (Simmonds, 1988).
3. Availability of Chemicals for Analysis and Aflatoxin Control
For quick and efficient analysis, chemicals should be readily available. In most cases, reagents for aflatoxin analysis are usually imported (Garcia and llag, 1986). These chemicals may only be available in big cities of the Asian countries. Perhaps, this could be attributed to the fact that aflatoxin is not yet known especially in the hinterland villages.
Chemical control has been reported to be one of the alternatives for aflatoxin control but chemicals intended for this purpose may not be readily available and might be very expensive. In addition, farmers may not be familiar with the correct application procedure (llangantileke, 1987).
4. Scarcity of Highly Trained and Experienced Personnel
Effective research needs experienced and highly trained personnel. In countries like U.S.A., U.K. and the rest of those pioneers in aflatoxin research, highly qualified personnel may not be a problem. In developing countries however, there is a dearth of trained personnel to embark on large scale multidisciplinary programs for the prevention and control of aflatoxins in various food and feed products (Ilag, 1984; Garcia and llag, 1986 and FAO, 1977).
5. Inadequate Facilities for Safe Aflatoxin Research
One of the major hindrances for a successful research program especially on dangerous substances like aflatoxin is the safely of the personnel. Those who are aware of aflatoxin health hazards, are unwilling to venture on this research activities if their health is at risk. Angsubhakorn (1989) cited cases where human risk was involved. He cited two chemical engineers in Czechoslovakia who worked on a method for sterilising peanut meal infected with Aspergillus falvus and subsequently died of lung cancer. One had worked for only three months and developed symptoms of lung cancer three months later. In another instance, two British biochemists developed cancer of the colon after exposure to purified aflatoxins. One of them had worked with aflatoxin for three years and developed symptoms seven years later. The second had done this work for 12 months end developed symptoms 2 years later.
6. Lack of Maintenance of Laboratory Facilities
Analytical laboratories must be properly maintained to obtain reliable and reproducible results. Sophisticated equipment for measuring minute quantity (in ppb) should be routinely checked for accuracy. However, highly trained personnel may not be always available in Asia or developing countries since most if not all of these sophisticated equipment are imported (Blanc, 1987).
7. Lack of Awareness on Aflatoxin Hazards
Prevention of aflatoxin contamination at the grassroots level is perhaps, the most effective method for aflatoxin control programs. It has been reported that aflatoxin is solely a postharvest problem but it was demonstrated by several researchers that infection starts when the crop is still on the field (Payne, 1986; Jones, 1986; Fortnum, 1986) because Aspergillus flavus is present in soil and air. Majority of the farmers are not aware of these findings. Some farmers would ignore the advise from their cofarmers especially when money is involved. These could be proven by non-adoption of improved postharvest practices to prevent aflatoxin contamination on freshly harvested produce. Similarly, middlemen and other grain handlers are not aware of all the danger of aflatoxin to both human and animals (FAO, 1977).
8. Stress Factors on Field Crops
Stress factors such as drought, floods, typhoons, etc. are beyond the control of the farmers. These factors would be aggravated in tropical and subtropical countries since warm and humid climate prevail. A relatively high incidence of aflatoxin in warmer areas of temperate regions and in subtropical and tropical climates have been reported. A typical example was the severe drought in Southwestern United States which caused economic damage on the maize farmers due to contamination of aflatoxin. Jones et al as cited by Payne (1986) reported that plants exposed to drought stress in the field had more infected kernels than samples from irrigated plots.
9. Inadequate Infrastructure
Infrastructure is divided into two parts, one would be the rural infrastructures which includes roads, bridges, etc. while the other would be the grain storage structures such as silos, warehouses and godowns. The former plays an important role in moving the freshly harvested produce to central drying facilities, storage structure and access to probable buyers. If these would be provided by the government in one country, there would be a free movement of crops intended for market. However, this would depend on the market price. Usually at harvesting time, the price decreases and farmers are reluctant sell their produce. They prefer to crib store their produce for 2 to 3 months before selling (RIO, 1988).
Grain storage structures are very important for preserving the quality of the produce. A safe storage place must be provided for the produce until it is needed for consumption since grain production is seasonal and consumption is continuous (Bailey, 1982). In developing countries such as in Asia, grain storage structures are still inadequate perhaps, due to the financial capability of most farmers to construct good grain storage structures.
10. Government Policies
Mycotoxin regulatory programs are being introduced in some Asian countries. These regulatory programs are introduced primarily to protect the export market of agricultural commodities. These regulations are being strictly enforced or else the importing countries would reject the commodities, resulting in a loss of valuable foreign exchange earnings. On the other hand, domestic regulatory measures on aflatoxins received very little attention. In India, mycotoxin legislations have been introduced but the implementation was found to be inadequate. This might be due to the interference connected to businessmen dealing with aflatoxin products. Most farmers feel that it is another government ploy which calls for additional investment with no incentives given for the aflatoxin free produce (Bhat, 1987). There has been no heavy penalty on the violators of aflatoxin regulations.
Aflatoxin contaminated products are allowed to enter in the market. Governments should have a regulation to reject those food and feedstuffs which have an aflatoxin level above the acceptable limit. However, an equipped laboratory would be needed with adequate and well-trained staff to perform such analysis.
11. Trade Practice
Trade of agricultural produce in most countries is carried out by weight. As much as possible the farmers prevent loss of excessive moisture to have a high income or return of their produce. This situation is a good entry of toxigenic fungi (FAO, 1997).
In groundnut trade, hand-picked selected (HPS) produce commands higher demand due to minimal or no damage. The damaged groundnuts would be for local or domestic trade, thus increasing the chance of ingestion of contaminated groundnuts by the local community. This has been manifested by a high incidence of primary liver cancer in Asian countries since no special attention is given on the produce for home consumption. A common practice is to set aside produce with good quality while the rejects would be for home use (FAO, 1977).
The damaged groundnut would usually be destined for oil mills. It has been reported that oil has high aflatoxin levels and unrefined oil is still consumed extensively in preference to refined oil due to the high cost of the latter.
Also, most traders have poor storage facilities. During storage, the produce would be most likely attacked by insect pests which would provide a ready access of toxigenic fungi into the grain and subsequent mycotoxin contamination. Moreover, businessmen hoard the produce during the lower price stage and sell them when the price is favorable.
12. Inadequate Extension Programs
Considerable information has been gathered concerning the conditions that lead to mould growth and mycotoxin contamination during growing, harvesting and storage of crops on the farm and on the practices that can be followed to avoid or minimize contamination. Information is also available on the levels of aflatoxin in feeds, safe storage and handling practices, transport of agricultural commodities, selection of foodstuffs by housewife and other related informations. However, all this information may not reach the farmers, traders and all those who need to be informed, due to inadequate extension services, lack of community and demonstration agents, non-existence of farm organisations, non-cooperation of traders organisation and no regular radio and television programs (FAO, 1977).
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