Groundnut

Aflatoxins

Introduction Foreword Aflatoxin Producing Fungi Toxic Effects Of Aflatoxins Factors Responsible For Aflatoxin Production Control Of Aflatoxins

Introduction

  • Aflatoxins are toxic metabolic substances produced by certain toxigenic strains of Aspergillus flavus and A. Parasiticus fungi growing in various feed and food commodities.
  • They are the most potent hepatocarcinogens among all the known natural and synthetic compounds.
  • Historically, the most fatal effect of aflatoxin was the report of heavy loss of turkey poults in the UK, where more than 10,000 young turkeys died in 1960.
  • The disorders was then tentatively named as ‘Turkey-X-Disease’. In turkey birds, this disease was characterized by loss of appetite, lethargy and a weakness of the wings followed by death within a week or so.
  • The factor for the disease was known to be incorporation of Brazilian groundnut metal into the rations of livestock and poultry.
  • The meal was examined for several possible causes and finally it was found to be contaminated with Aspergillus flavus.
  • The toxic principle was isolated from the contaminated groundnut meal and named as "aflatoxin" where ‘A’ stands for Aspergillus, ‘fla’ for flavus and ‘toxin’ for poison.
  • Thus aflatoxin was established as the cause of ‘Turkey-X-Disease’. Difurano coumarin compounds designated as aflatoxins have been discovered since then.
  • A very small amount of aflatoxin in feed (10-20 ppb) can produce fatal liver cancer in young animals.
  • Aflatoxins have also been implicated in human diseases.
  • The amount, kind and composition of aflatoxin produced vary with the substrate, environment, and the strain of Aspergillus of Aspergillus flavus (and consequently the production of aflatoxins).
  • Aflatoxin contamination is a serious quality problem in groundnut.
  • High aflatoxin load in HPS-grade kernels and deoiled cake has seriously jeopardized our export earnings.
  • Thus, aflatoxins have become the subject of concern in agriculture, as well as in animal and human health on a global scale.

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Foreword

  • India was an important exporter of groundnut and its products till the seventies.
  • In eighties our country exports a remarkable quantity of groundnuts and groundnut cake.
  • But the higher Aflatoxin load in the exportable commodities like groundnut kernels and de-oiled cake has seriously jeopardized the export earnings presently ,thereby depriving the country of valuable foreign exchange.
  • India is making concerted efforts to control the growth of the causal organism, Aspergillus flavus ,on groundnut through a variety of methods.
  • Identification and development of varieties resistant to A.flavus and aflatoxin is an area which is receiving considerable attention.

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Aflatoxin Producing Fungi

  • Fungi A flavus produces aflatoxins. Some other fungi have also been reported as aflatoxin-producers, but the reports need confirmation.
  • A flavus is a normal constituent of the microflora in air, soil and water and is associated with living or dead plants and animals throughout the world.
  • A flavus has also been reported as a pathogen of man, animal and plant.
  • All the strains of A. flavus are not capable of producing aflatoxins.
  • It has been reported that the aflatoxin-producing potential of the isolates mainly depends upon their genetic make-up although the rate of growth, morphology and chemical composition of toxigenic and non-toxigenic strains may be identical.
  • A flavus is recognized by its yellow-green to blue-green colour. During their metabolism these fungi not only produce aflatoxins but also deteriorate the nutritive value of the associated food commodities.

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Toxic Effects of Aflatoxins

  • Aflatoxins are carcinogenic (cancer-producing) and mutagenic (having power to produce mutation) in their biological activity.
  • The LD50 values (the dose required to kill 50% of the treated animals) for ducklings were 18.2, 84.8, 392 and 172.5 Mg of B1, B2, G1 and G2, respectively, indicating that aflatoxin B1 is most toxic.
  • Liver is the organ principally affected, in which the toxins induce malignant hepato-cellular carcinomas.
  • However, in a few instances tumors of other organs, especially the kidney, are associated with aflatoxins.
  • A total dose of 3.6-10 mg of aflatoxin was found to induce hepato-cellular carcinomas in Fischer rats with a frequency of 100%.
  • Aflatoxins were also implicated in an outbreak of hepatitis in India in 1974 in tribal areas covering more than 200 villages of Rajasthan and Gujarat. The outbreak lasted for about 2 months and was confined to the population whose staple food was maize, which was found to be contaminated heavily with A. Flavus. Analysis of the contaminated samples revealed that affected people might have consumed between 2 and 6 mg of aflatoxin daily over a period of few weeks.
  • It has also been reported that in Indian children there exists a condition commonly known as ‘Indian Childhood Cirrhosis’ due to the consumption of groundnut contaminated with aflatoxin. The disease is known to be predominant in early stages of child growth (at the age of 3 years) affecting the liver cells, causing degeneration, fibrosis and hepatomegaly and in advanced stages proceeds to jaundice, ascites and hepatic coma. It has been reported that cirrhosis occurs not only in India but all over the world, especially in the tropical countries.

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Factors responsible for Aflatoxin Production

  • The nature of the strain of the fungus, substrate, pH, temperature relative humidity, moisture content of the substrate and aeration have been found to influence the quality and quantity of aflatoxins produced.
  • The optimum limits for growth of A. flavus and A. parasiticus are 82-85% relative humidity and temperature of 30-32oC.
  • Fungal growth is optimum when moisture levels of the substrate range from 10 to 30%.
  • The optimum conditions for aflatoxin production are between 25oC and 30oC at 85% relative humidity.
  • When the atmospheric relative humidity is near 70%, the seed moisture content will equilibrate between 7 and 9%, which is a level unfavourable for the growth of the A. flavus group.
  • Premature drying of pods and shell damage and kernel splitting during growth may lead to toxicity at harvest.
  • These conditions may result from termite and nematode damage to the root pods during weeding and other intercultural operations, drought, and long exposure of groundnut pods after harvest to atmosphere congenial to the growth of fungus.
  • During storage, presence of mites which are capable of carrying the spores of A. flavus increased the chances of infection.

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Control of Aflatoxins

  • In view of the know hepatotoxic properties of aflatoxins, their widespread occurrence during cultivation, harvest, drying, storage and transit of groundnut and also loss of HPS (Hand picked selected) export markets, immediate attention and efforts are needed towards achieving effective control measures.
  • Three basic approaches – prevention, removal and detoxification – seem to be promising for aflatoxin control. Of these, prevention is considered to be the best.

Use of resistant varieties:

  • The development of varieties which would resist seed invasion and support less aflatoxin production would be an ideal remedy. The following genotypes have been identified as resistant to A. flavus invasion and colonization by various research centres and institutes.
  • NRCG Junagadh : ‘CGC 2;’CGC7;, ‘1-4’, ‘1-7’, ‘S’ 230’; breeding lines of cross ‘S’230’ x ‘PI 337394 (F) and Latur 33 x PI 337394 (F)’.
  • ICRISAT, Hyderabad : ‘Ah 7223’, ‘Var.27’, ‘Faizpur’ and ‘Monir 240-30;
  • NIN, Hyderabad: J-11; Karad 4-11; Kopergaon 1and US 26 (PI 246388);

Prevention:

  • Preventive measures constitute the best approach to minimize the contamination of groundnut and its products by Aspergillus group of fungi and their toxins.
  • The following are some of the preventive measures for avoiding aflatoxin contamination in groundnut:
    1. Avoid mechanical and biological damage to the crop particularly during cultivation, harvesting and subsequent processing.
    2. Use supplemental irrigation during drought to avoid plant stress.
    3. Harvest the crop at peak maturity and use inverted windrows to optimize curing.
    4. Dry the produce as rapidly as possible but the rate of drying must be controlled to prevent excessive skin slippage and splitting of kernels. When the crop is harvested under wet conditions the pods should be picked and sun-dried immediately.
    5. Dry groundnut pods to a safe moisture level (8%) before storage.
    6. During drying, grinding and extraction of oil, batches of produce originating from different places are mixed. It is desirable to remove the contaminated pods and kernels either manually, or mechanically, or by using electronic devices. Wherever groundnut kernels or flour forms a large part of the human diet as a major source of protein, the risk is reduced by hand sorting.
    7. Store the produce at low temperature and humidity.
    8. Avoid rewetting of groundnut meal by storing under dry condition and proper packing during transit.
    9. Based on the results obtained at the National Research Centre for Groundnut the use of rock salts (2%), plant products like asafoetida (hing), 0.1% if pure and 2% if impure, turmeric powder (2%) and aqueous leaf extracts of 'neem' and 'mehndi' (henna) has been suggested for Preventing aflatoxin contamination in groundnut.

Detoxification:

  • Techniques that remove or destroy aflatoxins from samples must be applied only if Preventive measures have failed, and not as an alternative to good agricultural and storage practices.
  • A detoxification Process must be technically and economically viable and may be used if the process:
    1. Destroys or inactivates the mycotoxins.
    2. Does not produce or leave toxic or carcinogenic residues in the final product.
    3. Destroys fungal spores and mycelia which could under favourable conditions, proliferate and form new toxins.
    4. Preserves the nutritive value and acceptability of the product.
    5. Does not significantly after important technological properties.

Physical methods

  • Physical techniques like autoclaving and exposure to gamma-irradiation were useful in reducing aflatoxins.
  • Autoclaving at 120oC and at 0.0105 kg/mm2 is known to reduce toxins from 9,000 ppb to 350 ppb.
  • Gamma-irradiation at a level of 5 M rad would destroy 80% of the aflatoxins in a sample.
  • At the CFTRI, Mysore, a simple method for inactivation of aflatoxin in oil has been developed. In this method unrefined oil in glass bottles is exposed for one hour to bright sunlight.
  • Aflatoxin is photo-degraded and is reported to lose its toxicity.

Chemical methods

  • Aflatoxins can easily be extracted from the contaminated sample through the use of some solvents like acetone and isopropyl alcohol.
  • Inorganic solvents like l% sodium bicarbonate of 1% calcium chloride could effectively remove the toxins up to 80% However, these methods also remove some nutritional constituents like proteins.
  • This method can be used at the household level since salt is readily available.
  • Application of 0.5% hydrogen peroxide was reported to reduce the aflatoxin levels from 1,000 ppb to 25 ppb.
  • Methoxymethane (dimethylether) was reported to be useful in removing aflatoxin from contaminated groundnuts and groundnut meal.
  • Some processes like sun-drying, exposure to burning cowdung fumes and spray of 1% common salt were useful in detoxification of aflatoxins to the levels ranging from 10 to 50%.

Detoxification using ammonia

  • Treatment with ammonia is the most promising process for detoxification of aflatoxins.
  • The oilseed cake containing 12-15% moisture is treated with ammonia gas under pressures of 2 to 3 atmospheres for 15 to 30 minutes at a temperature of around 90oC.
  • By this method aflatoxins to the extent of 95% get destroyed Toxicological studies carried out on the ammonia-treated oil cakes revealed that the product realized by ammonification is safe for edible purposes.

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Uttar Pradesh