Mycotoxin in Edible Nuts, oilseeds, and Legumes

Food commodities like nuts, oilseeds and legumes are major dietary constituents which are widely consumed across world in form of traditional food or as a functional ingredient in processed foods. These constituents also help in combating various lifestyle associated chronic disorders as these are enriched in dietary proteins, fiber, polyunsaturated fatty acids, and phytochemicals. However, these materials, due to their physical and chemical composition, are particularly susceptible to mycotoxin contamination due to the presence of filamentous fungi/molds. Mycotoxin contaminated can occur any time during supply chain, either during vegetation in the field or during storage, as well as during the processing.

Mycotoxin  based contamination appears to be one of the major causes for economic losses of food and feed stuff and generating health-related risks posing serious health threat to both humans and livestock. Mycotoxins are low molecular weight secondary metabolites that are naturally produced by certain molds in food products under warm and humid conditions. Mycotoxins appear in the food chain as a result of mould infection of crops both before and after harvest. Most mycotoxins are chemically stable and can survive food processing.  The adverse health effects of mycotoxins range from acute poisoning to long-term effects such as immune deficiency and cancer. Exposure to mycotoxins can happen either directly by eating infected food or indirectly from animals that are fed contaminated feed.

Several hundred different mycotoxins have been identified, but the most observed mycotoxins that present a concern to human health and livestock include aflatoxins, ochratoxin A, fumonisins, zearalenone and deoxynivalenol. The major toxigenic fungal genera are Aspergillus, Penicillium and Fusarium producing a diverse group of mycotoxins with adverse effects. Insect infestations and damage play a major role in fungal infection and mycotoxin contamination. Insect control either through pest control, breeding or genetic engineering of resistant cultivars and/or biological control through the application of non-toxigenic strains is a promising tool to reduce mycotoxin contamination.

A. Classification of Mycotoxin Flora:

Fungi contaminating nuts, oilseeds and legumes have been conventionally divided into two groups:

  1. Field Fungi: Field fungi are those that infect the crops throughout the vegetation phase of plants and they include plant pathogens such as FusariumAlternaria, and Botrytis  .
  2. Storage Fungi: This group include Aspergillus, PenicilliumRhizopusand Mucor genera that infect grains after harvesting i.e., during storage.

B. Types of Mycotoxins 

  1. Aflatoxins:

The aflatoxins are the major mycotoxin contaminants of peanuts, hazel nuts, pistachio nuts, almonds, brazil nuts, walnuts and therefore the most important mycotoxins entering the human food chain upon consumption. A. flavus and A. parasiticus are the major producer of this secondary metabolite. These are the family of closely related compounds which includes aflatoxin B1, B2, G1 and G2 and AFB1. AFB1 is considered as the most toxic one among mentioned classes of aflatoxins. Based on the acute aflatoxin poisoning in India, an LD50 of approximately 5mg/kg body weight has been proposed in humans.

  1. Ochratoxin A (OTA)

It is produced by P. verrucosum and P. nordicum and by a few Aspergillus species including A. carbonarius and A. niger. The mycotoxin occurs on a wide variety of food products including coffee, grapes, beans, chickpeas, and nut seeds such as pecans and pistachios. OTA exhibits immunosuppressive, nephrotoxic, nephrocarcinogenic and teratocarcinogenic effects. The formation of DNA adducts, and the induction of oxidative stress have been proposed as possible mechanisms involved in OTA nephrocarcinogenic, which was classified as a group 2B carcinogen or possibly carcinogenic in humans. Involvement of OTA in the development of chronic renal disease and kidney and urinary tumors have also been reported.

  1. Deoxynivalenol (DON)

It is one of the major trichothecene mycotoxins produced mainly by Fusarium graminearum, F. culmorum and F. crookwellense which mainly infects the food commodities like maize, millet, sorghum and soybeans and rice. The major acute toxic effect of DON is related to feed refusal, vomiting and severe gastrointestinal toxicity in animals. Other effects include teratogenicity, cardiotoxicity, and disruption of the immune system.

  1. Zearalenone (ZEA)

It normally co-occurs with DON and exhibits its activity by binding to estrogen receptors altering the estrogen responsive elements in the nucleus. ZEA also interferes with steroid metabolism and hence could be involved in the disruption of the endocrine system and has been shown to increase liver cell and pituitary tumors in mice. ZEA, α-zearanol and the type B trichothecene, 15-acetyl DON, are consistently detected in soybean oil.

  1. Fumonisins:

It is mainly produced by Fusarium verticilioides , F. proliferatum and  A. niger. It cause a wide variety of toxic syndromes in animals, and depending on the animal species could affect the liver, kidneys, lungs and brain. They have been associated with the development of liver and esophageal cancer and neural tube defects in humans. Fumonisins have been classified as apparent non-genotoxic carcinogens that exhibited their mode of action via the disruption of lipid biosynthesis and hence the structure and function of cellular membranes.

Exposure to mycotoxins needs to be kept as low as possible to protect the people. Mycotoxins not only pose a risk to both human and animal health, but also impact food security and nutrition by reducing people’s access to healthy food. WHO encourages national authorities to monitor and ensure that levels of mycotoxins in foodstuff on their market are as low as possible and comply with the both national and international maximum levels, conditions and legislation.



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