Prevention and control of mycotoxins in foodgrains in India
Contents - Previous - Next
R. K. Goyal
Assistant Director (S&R)
Ministry of Food & Civil Supplies
Department of Food
Indian Grain Storage Institute, Hapur 245101, India
India is predominantly an agrarian country with nearly three fourths of the people dependent on agriculture or rural economy. The most outstanding achievement of Indian agriculture since independence is the phenomenal growth of foodgrains output. During the last three decades, Indian agriculture has experienced a revolutionary breakthrough in foodgrain production leading the country from deficit and import arena to the positive situation of self-sufficiency and buffer stocks. The foodgrain production in the country increased from 50.8 million tonnes in 1950-51 to 152.37 million tonnes in 1983-84, but the growth of Indian agriculture still continues to be linlked with the vagaries of nature. Some of the states in the country have come across the unprecedented draught of the century for the fourth successive year which has caused tremendous hardship to the people as also loss of production of foodgrains in those states.
Nearly seventy percent of the total production of foodgrains in India is retained at farm level where the unscientific and faulty storage conditions enhance the chances of fungal attack and thereby mycotoxin production. The decomposers of foodgrains i.e. fungi, bacteria etc. are always present on foodgrains in dormant conditions (usually as spores) and grow under favourable climatic and other conditions (1). The fungal growth may cause decrease in germinability, discolouration of grain, heating and mustiness, loss in weight, biochemical changes and production of toxins. All these changes may occur before the responsible fungi could be detected on visual examination (2).
The fungi produce a large number of mycotoxins in foodgrains and their products. Mycotoxins are a group of highly toxic secondary metabolises of the fungi produced under certain favourable environmental conditions (3). Because of their potent toxic nature and fairly common occurrence under natural conditions, mycotoxins have attracted world-wide attention in the recent years. The diseases or physiological abnormalities resulting due to ingestion of mycotoxins are known as "mycotoxicosis" (4).
2. GENESIS OF THE PROBLEM
Association of mould produced toxins with food commodities has been knowri since Biblical times but their role in inciting disease syndrome was realised only when it was discovered that "ergotism" was caused due to consumption of barley and rye infected with Claviceps purpurea (5). Cardiac beriberi caused by Penicillium citreovirde was recorded in Japan due to consumption of contaminated rice; Stachybotryotoxicosis of horses in Soviet Union in 1931; Red Mould Diseases or Black Spot Diseases Caused by Fusarium sps. in Japan during 1940-50 and Alimentary Toxic Aleukia (ATA) caused by Fusarium and Cladosponum species in USSR during 1942-47 (6).
The severity of mycotoxin problem was realised during World War II when Russians eating mouldy overwintered grains sufferred with severe dermal necrosis, leukopenia, haemorrhages and destruction of bonemarrow._ Fusarium was found to be the causal organism (7). World-wide scientific recognition of mycotoxin problem was, however, only in 1960 when it was discovered that the aflatoxins were responsible for the death of about a lakh turkey poults (Turkey x disease) in England (8). According to Blount, the "poisonous feed" which caused the havoc and which was the preparation of Brazilian peanuts, was contaminated with Aspergillus flavus (9).
3. NATURAL OCCURRENCE OF MYCOTOXINS IN INDIA
Cereals constitute the most important food and feed sources which are affected by various mycotoxic fungi. The problem of natural occurrence of mycotoxins in cereals aggravated to some extent due to rapidly changing agricultural technology (10). In general, mycotoxins and particularly aflatoxins seem to pose great problem in the tropics than in the temperate regions but no part of the world can be considered to be mycotoxin-free zone due to the movement of various foodstuffs from one part of the globe to the other (4).
Some of the important commodities which have been found to be naturally contaminated with one or the other mycotoxins are listed below:
Maize is an excellent substrate for mould growth and mycotoxin production. In India, systematic survey of maize grains for mycotoxins contamination has been undertaken in some parts only. However, some reports mainly on aflatoxin contamination in stored grains have indicated that the problem of aflatoxin contamination is much more serious than usually visualised (4). In an extensive survey of the important maize growing areas of Bihar, natural contamination of mycotoxins and particularly of aflatoxin was reported in the grains of field maize crop (11). Surveys conducted by the Indian Grain Storage Institute during 1978-79 and 1980-81 indicated contamination of stored maize grain samples with aflatoxin B1 in the range of 40-510 ppb (12,13).
Under a FAO sponsored Food Contamination Monitoring Project, out of 10 maize samples collected from Western Uttar Pradesh, 3 samples were found contaminated with aflatoxin B. in the range of 20-80 ppb (14). Samples of maize collected from traditional storage structures from various parts of India have shown contamination of aflatoxin B1 in the range of 15680 ppb (15). Fifteen varieties of maize were screened by Bilgrami et al (16) for aflatoxin production by artificial inoculation of A. parasiticus. Practically ail the varieties favoured aflatoxin production, but in varying degrees. Maize is a good substrate for the production of Zearalenone which has been detected frequently in commercial varieties. Reports of natural occurrence of Zearalenone in standing maize crop are also available (4).
Rice is also one of the important cereals which favours mycotoxin production. Natural occurrence of aflatoxin and aflatoxin producing fungi in rice has been reported from various parts of the world (16). In a survey of paddy harvested from rain affected crop in Punjab and Haryana, out of 83 samples only 3 ewre found contaminated with aflatoxin B. in the range of 10-40 ppb (17,18). Rice stored for prolonged periods i.e. 4-8 years has also been reported to be contaminated with aflatoxin B. in various parts of India (12, 13, 14, 15, 10, 20, 21).
Presence of some other mycotoxins like citrinin, Sterigmatocystin and Ochratoxin has been detected as natural contaminants of rice in one or the other region of the world. Only scanty information is available pertaining to these toxins in India (4).
Wheat does not appear to be a good substrate for aflatoxin elaboration. Survey reveals that natural contamination of wheat occur but in low profile (30). Out of 223 samples collected from wheat growing belt of Western U.P. (India), only 9 samples were found contaminated with aflatoxin B. in the range of 8-40 ppb (4,19,22). In 1985, all the six flood affected wheat samples collected from Punjab were found contaminated with aflatoxin B1 in the range of 8-40 ppb (24). There are few other reports of the natural contamination of aflatoxins in wheat in India (23, 31). Reports of natural occurrence of Sterigmatocystin in the domestic and imported red & white wheat are also available from India (32).
3.4 Barley, oats, millets etc.:
Like wheat these small grains also do not favour natural contamination of mycotoxins. However, some of these grains have been reported suitable substrates for aflatoxin production. All the four aflatoxins B1, B2, G1, G2 as natural contaminants were isolated from sorghum grains obtained from ears affected by A. flavus in North India (25). In Western India sorghum samples were found contaminated with aflatoxin B., the level of which was significantly correlated with moisture content as well as A. flavus population (26). A survey in Central U.P. (India) has indicated that sorghum and bajra are also naturally contaminated with aflatoxin B. during storage (19). It was also noticed that contamination of aflatoxin degraded quantity-wise with the increase in storage period during May to September. Perhaps, it was because of the fact that the production of aflatoxin diecreases with increase in the temperature beyond 25°C. Out of the total contaminated samples, only 2 samples of sorghum contained 40 ppb, beyond the prescribed limit of 30 ppb for food in India.
3.5 Pulses & Oilseeds:
A survey under FAO sponsored Food Contamination Monitoring Project in Western Uttar Pradesh revealed that few samples of pulses including green gram, black gram & lentil and few samples of cotton seed were found contaminated with aflatoxin B1. The range being 4-80 ppb in pulses and 35-200 ppb in oilseeds (14). Similarly, ten percent of stored soybean samples were found contaminated with aflatoxin B. in the range of 4-40 ppb, in a survey in Uttar Pradesh (27).
A survey carried out by the Central Food Technological Research Institute, Mysore and Regional Research Laboratory Hyderabad revealed that 80 percent of the peanut meal produced in different states in India was found contaminated with aflatoxin at varying levels (28).
3.6 Dry fruits & spices:
Aflatoxin has been reported as the main contaminant of coconut and other dry fruits viz. almond, cashew nut, walnut, raisin, makhana and emblic. In some samples of these dry fruits, presence of Zearalinone, Citrinin and Ochratoxin has also been reported. Natural contamination of aflatoxin in various samples of chillies, fennel, cumin, coriander, black pepper, ginger, cardamom and turmeric and presence of Orchratoxin, Citrinin and Zearalinone has also been reported in a few samples of spices (33). In a limited survey in Uttar Pradesh conducted by the Indian Grain Storage Institute, Hapur during 1984-85, it was revealed that out of 99 dry fruit samples only 19 samples were contaminated with aflatoxin B1 in the range of trace to 50 ppb (19).
3.7 Milk & Milk Products:
Milk and milk products are consumed by the people of all age groups and are also important sources of mycotoxin exposure. So far no systematic survey of milk or milk products has been done in India (33). Some reports indicate that aflatoxin M, upto 8 mg/l were detected in the milk of buffaloes in Andhra Pradesh (34).
3.8 Cattle & Poultry Feed:
Cereals and oilseeds constitute more than 70 percent fraction of cattle and poultry feed. Usually, the food which is declared unfit for human consumption finds its way as feed for animals and poultry birds (33). A number of reports indicated the presence of high concentrations of aflatoxins as natural contaminants in cattle feed. Presence of Ochratoxin A and Sterigmatocystin has also been shown in some samples of cattle feed containing sunflower cake and green gram (35).
4. HIGH RISK AREAS IN INDIA
Being aerobic in nature, mycotoxic fungi require air, moisture, nutrients and suitable temperature for their growth and metabolism (4). Moisture content of the grain or the relative humidity surrounding the substrate are the most important factors governing the growth and aflatoxin production by A. flavus. Climatic conditions in India are most conducive for mould invasion proliferation and elaboration of mycotoxins. The high risk areas identified in India are Kerala, Western India, Gangetic plains, north eastern as well as coastal areas of Andhra Pradesh, Karnataka and Tamil Nadu (16). Unseasonal rains, flash floods are very common in India which enhance the moisture content of the grain making them more vulnerable for fungal attack (30).
5. PROBABILITIES OF CONTAMINATION
Warm humid climate provides congenial atmosphere for the growth of fungi and production of toxins. Aspergillus flavus which is known as storage fungi may infect and produce aflatoxins in crops in the fields also (30).
Foodgrains are normally harvested at higher moisture content and then dried to bring down the moisture content up to safe level before storage. Delay in drying to safe moisture levels increases risks of mould growth and mycotoxin production.
Natural calamities like floods or torrential unseasonal rains during pre, mid or post-harvest stages may render the crops vulnerable to microbial attack. Annual loss due to spoilage of high moisture paddy is conservatively estimated to be 10-15% of the total production of paddy, produced during rainy season in India (22).
Faulty storage conditions may also enhance the chances of microbial attack and production of mycotoxins. Thus, starting from harvesting of the crop till the food or food products are consumed by the consumers, there are chances of microbial invasion/fungal attack at each and every stage/step.
6. R & D CENTRES FOR STUDY OF MYCOTOXINS IN INDIA
Considerable R & D work on mycotoxin contamination is being carried out at the following centres:
Eighteen countries all over the world have guidelines or regulations which prescribe maximum acceptable limits for aflatoxins in food and feeds.
The limits prescribed vary from 0 to 50 ppb in foods and from 0 to 1000 ppb in feeds (30). The Protein Advisory Group of United Nations has recommended intake maximum 30 ppb aflatoxin in foods rich in protein, where use of contaminated food cannot be avoided.
In India, the Governmental agencies procure foodgrains confirming to prescribed specifications thereby minimising the chances of contamination and thus ensure the supply of good quality foodgrains to the consumers through PDS. At farm level also quality consciousness is created amongst the farmers through a network of 17 teams of Save Grain Campaign. These teams educate, motivate and persuade the farmers to adopt scientific methods of foodgrains storage with a view to minimise the qualitative and quantitative losses in foodgrains during storage likely to occur due to insects, rats and moulds. The Quality Control Teams monitor the quality of foodgrains at commercial level.
8. PREVENTION AND CONTROL OF MYCOTOXINS
Hazards of mycotoxin infected food are now well recognised. Considerable concern has, therefore, been shown in the recent years towards the control of these toxic metabolises. Control is attained by preventing the growth of moulds, separation of infected grains, detoxification and by growing resistant varieties (33).
8.1 Prevention of mould growth:
In stored grain, mould damage may be prevented mainly by three kinds of methods viz. drying of grain, controlled atmosphere storage and chemical treatment.
8.1.1 Drying of grain: It is an established fact that dry grain stores long, safe from insects and moulds because the requirements of moisture for their development are not met. The average Indian farmer perform drying of grain conventionally under direct sun light (36). The most widely used indigenous practice of grain drying is to spread threshed grains in thin layers on Kachcha floor with cow-dung in the open sun and stirring it by human labour till the grains are dried to safe level. Some farmers have also been using Pucca floors. Sun drying of grains on Kachcha surface was quicker as compared to Pucca surface, transparent polythene & black polythene. 5.30 percent loss in the moisture content of maize dried in sun-light could be achieved during 8.5 hours time (36). Exposure of aflatoxin contaminated groundnut oil to sun light has given very promising results as it destroyed about 99 percent of the aflatoxins (4). Other methods of grain drying include mechanical drying, in-bin drying, infrared, microwave or sonic and solar energy drying. Researches are being conducted to employ these methods also (37).
81.2 Controlled atmosphere storage: The significance of underground storage lies behind the philosophy of grain cooling and depleting the oxygen content to the desired level whereby the microbes and insects cannot grow. Air-tight storage also works on the same phenomenon where the depletion of oxygen by grain respiration manipulates disinfection by inhibiting aerobic fungi, elimination of mycotoxin production and conservation of desirable quality factors in the grain. Natural cooling is another effective method of preserving grain. The low temperature does not allow the microflora to grow as most of them are thermophillic.
8.1.3 Chemical treatment: Chemical control of fungal deterioration to stored grain is restricted to the treatment of grain for seed purposes only but not for food and feed. Experiments conducted by Indian Grain Storage Institute showed that "Grain treat" (Mixture of propionic acid, acetic acid and benzoic acid) against Aspergillus & Penicillium sps. did not produce effective results in maize. Seed treatment with Bavistin and TMTD (Trimethyl thiuram disulphide) at 0.25 per cent concentration gave 100 per cent protection to wheat grain in one year storage against Aspergillus and Penicillium sps (37). Certain mild phenolics like perulic acid and O-Vanillin have also been reported to prevent aflatoxin production on rice, wheat, maize, groundnut and mustard seeds (33).
8.2 Separation of infected grains:
Physical separation of infected grains is an efficient and feasible method of minimising mycotoxin contamination. This is effected either by manual operation or with the help of an electronic sorter. Fungal infection of seeds or grain usually imparts characteric colour or other physical properties.
Cooking at atmospheric pressure can destroy about 50 percent of the toxins. Dry roasting and oil roasting of groundnut reduces aflatoxins to a significant degree. Cooking rice under 15 Ibs. pressure for 5 minutes gave maximum destruction of aflatoxins (72 percent) as compared to ordinary cooking or cooking with excess water. Light has also been employed successfully to destroy aflatoxin in crude groundnut oil. Studies have shown that visible light is more effective than either ultra-violet or infra-red light (30).
8.4 Growing resistant varieties:
In view of the hazardous effects of mycotoxins, efforts are being made to develop mould resistant varieties which will be mould free not only in fields as standing crops but during storage also they will restrict development of moulds.
List of important mycotoxins, producer fungi and principal toxic effects
|Mycotoxins||Producer fungi||Principal toxic effect|
|Aflatoxins||Aspergillus flavus,||Potent carcinoge-|
|A. oryzae,||nic, mutagenic,|
|Patulin||P. patulum,||Induces subcutane|
|P. expansum||ous sarcomas|
|Penicillic acid||P. pulberulum,||Cell necrosis|
|Trichothecenes||F. poae, F. roseum||Teratogenic,|
EEC Tolerance limits for aflatoxin B.' in animal feed
|Sl. No. Commodity||Aflatoxin B1 tolerance not more than (µg/kg) or ppb.|
|1. Produce for processing into mixed feed||50|
|2. Complete feed for cattle, sheep and goats (with the exception of dairy animals, calves and lambs)||50|
|3. Complete feed for pigs and poultry (with the exception of infant pigs, chicks, ducklings and turkeys).||20|
|4. Animal teed supplements for dairy animals||20|
|5. Other complete feeds.||10|
Aflatoxin Limits in Different Countries
|Country||Commodity||Aflatoxin limit (µkg or ppb.)|
|1. Belgium||Animal feed||40 ***|
|2. Brazil||Ground oilseed cake (export)||50|
|3. Canada||Nuts and their derived products||15 **|
|4. Denmark||Groundnuts & Brazil nuts||5-10|
|5. France||Animal feed||700|
|6. India||Groundnut kernel||30|
|7. Israel||All foods||20|
|9. Japan||All foods||10|
|10.||Groundnuts cake for animal feed mixes||1000|
|11. Malaysia||All foods||0|
|13. Netherlands||Foods & Feeds||5|
|14. Norway||Oilseed cake||600|
|15. Poland||All foods and feeds||5|
|17. Sweden||All foods particularly|
|Brazil nuts, groundnuts,|
|Raw-materials for further|
|processing in Sweden||20|
|18. U.K.||Confectionery, groundnuts,||50|
|Groundnut flour for|
|animal feeds||0 - 500 ***|
|19. U.S.A.||Confectionery, groundnuts||20*|
|All foods & animal feeds||20 - 25|
* Aflatoxin B
** Total of aflatoxin B1, B2, C1, C2
*** See Table-3 - EEC limits may apply.
Contents - Previous - Next