Under the shell of peanut #2. Aflatoxins

Last Saturday we started to talk about peanut “sensitive topics”, particularly, about the loss of vitamins, minerals, other constituents during peanut processing.

Another peanut “sensitive topic” is CONTAMINATION WITH AFLATOXINS.

What are AFLATOXINS?

Aflatoxins are a family of toxins (secondary metabolites) produced by certain fungi Aspergillus flavus and Aspergillus parasiticus.

Long-term exposure may lead to serious health problems. It increases the risk of cancer (have cancerogenic effect), acute poisoning (in large doses), immunotoxicity (may decrease resistance to infections), growth impairment in children and acute liver failure (lethargy, nausea, even death).

Aflatoxin B1 (AFB1) IS the most toxic form of the aflatoxins.

Aflatoxin sources in food crops

  • MAIZE
  • GROUNDNUTS
    • Arachis hypogaea – peanut; Arachis villosulicarpa – a perennial peanut species; Vigna subterranea – the Bambara groundnut; Macrotyloma geocarpum – Hausa groundnut
  • OILSEEDS
    • Mustard, Niger seed, sesame, soybean, cottonseed, soybean, or sunflower
  • TREE NUTS
    • Almonds, Brazil nuts, cashews, hazelnuts, pecans, pistachios and walnuts

Reasons of aflatoxin contamination

  • PRE-HARVEST CONDITIONS
    • drought stress and rainfall, insect damage, adaptation ability of crop genotype for its
    • climate, agricultural practices
  • POST-HARVEST CONDITIONS
    • food storage  
    • transportation
    • processing

Aflatoxins may develop in storage, after groundnuts had been harvested at the end of the wet season. Later (during the next harvest) it would be the cause of the elevated levels of aflatoxin in the dry season.

Aflatoxin exposure

According the WHO (World Health Organization) data in 2010, different countries have different levels of aflatoxin exposure to inhabitants.

  • Lowest aflatoxin exposure to inhabitants (less than 10 ng/kg bw/day*)

Argentina, France, Spain, USA

  • High aflatoxin exposure to inhabitants (more than 100 ng/kg bw/day)

Nigeria

Data for other regions differs too much to make certain conclusions. For example, in India it varied from 4 to 100 ng/kg bw/day; in Tanzania from 0.02 to 50 ng/kg bw/day

* X ng/kg bw/day means: X nano gram per kg body weight per day

Acute poisoning with aflatoxins

Large doses of aflatoxins (concentrations of 1 mg/kg or higher) lead to acute poisoning (aflatoxicosis) that can be life threatening, usually through damage to the liver. Adults are more tolerant to acute exposure than children.

Detecting aflatoxins

Detecting aflatoxicosis in humans and animals is difficult, however, novel aflatoxin-detection

Novel systems include dip-stick kits, hyperspectral imaging, electronic noses, molecularly imprinted polymers, and aptamer-based biosensors (small organic molecules that can bind specific target molecules).

Aflatoxins can be controlled

1. Pre-harvest control

  • Plant breeding or through genetic engineering
  • Biological control using another fungus, Aspergillus flavus.

The non-toxigenic strains of A.flavus occupy the same niches and are capable of competing and displacing the toxigenic strains of aflatoxins. This technique is applied to cotton, maize, peanuts, figs and pistachios in the USA; maize in Africa and Thailand; and peanuts in Australia, Argentina and China.

2. Post-harvest interventions

These are preventive measures to address adequate storage conditions: moisture, temperature, mechanical or insect damage, and aeration.

Other measures: chemical decontamination or enterosorbents are used to remove aflatoxins from already contaminated foodstuffs

Roasting may not help

Aflatoxins are highly resistance to heat. Therefore, roasting is not a guarantee to reduce its count.

Oppositely, one scientific study from Tabiz, Iran, showed that aflatoxin contamination in the salt-roasted samples was THREE TIMES higher than the pure ones. However, peanuts were least contaminated than pistachios and walnuts. Maybe the equipment was already contaminated? Who knows.

What the consumer can do?

  • Aflatoxin molds are not entirely killed by processing (roasting), so can show up in products, e.g. peanut butter
  • Carefully inspect whole grains and nuts for evidence of mold, and discard any that look moldy, discolored, or shrivelled
  • Buy grains and nuts as fresh as possible; that have been grown as close to home as possible, and which have not been transported over a long time
  • Buy only reputable brands of nuts and nut butters
  • Make sure that foods are stored properly and are not kept for extended periods of time before being used
  • Try to ensure diverse diet; this helps to reduce and mitigate aflatoxin exposure
  • Consumers who lack dietary diversity need to pay extra attention to minimize the risk of high exposure to aflatoxins. For example, extensive aflatoxin exposure has been reported from areas where people get a major part of their daily calorie intake from maize (i.e., Africa, Latin America)
  • Avoid high concentrations of nuts and grains in daily ration for people who are chronically infected with hepatitis B virus or have other liver chronic diseases

References

  1. Aflatoxins, Department of Food Safety and Zoonoses, Feb 2018, WHO; online source: https://www.who.int/activities/assessing-chemical-risks-in-food
  2. WHO estimates of the global burden of foodborne diseases, World Health Organization 2015; online source: https://apps.who.int/iris/bitstream/handle/10665/199350/9789241565165_eng.pdf?sequence=1
  3. Aflatoxins and growth impairment: A review. Pornsri Khlangwiset, Gordon S. Shephard, and Felicia Wu. Critical Reviews in Toxicology, 2011; 41(9): 740–755

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