Monday, 15 October 2018

Aflatoxins and Aspergillus Molds: Facts and Health Effects

Aflatoxins are toxic chemicals produced by specific molds that grow on food crops. The two molds that are most commonly associated with the toxins are Aspergillus flavus and Aspergillus parasiticus. The name “aflatoxin” comes from the scientific name of the first organism. Exposure to the toxins is known to increase the risk of liver cancer in humans and also has other harmful effects. The chemicals damage the health of animals as well as humans and also create economic problems when a contaminated crop needs to be destroyed. They are definitely chemicals that should be avoided as much as possible.

Peanuts have health benefits, but they are also susceptible to aflatoxin contamination.
Public domain image

Where Are Aflatoxins Found?

The crop types that are susceptible to the molds that produce aflotoxins include peanuts, wheat, corn, rice, millet, cassava, sunflower seeds, sesame seeds, and others. It’s not inevitable that a crop becomes contaminated with a harmful level of aflatoxins, however. There are steps that can be taken to keep a crop in good condition. Incorrect storage of a food is the most common cause of mold growth, but the mold may also grow on living plants in the field.

In the United States, the FDA (Food and Drug Administration) has set a limit for the level of aflatoxins in food. This level is occasionally found to have been exceeded and a food is withdrawn from the market. Incidents of aflatoxin poisoning are more common in some other countries, especially in those with both a high temperature and a high humidity. These conditions favour growth of the mold.

Aspergillus

Molds are a type of fungus. Like other fungi, their body consists of branching, thread-like structures known as hyphae. The hyphae of a fungus or mold is collectively known as a mycelium. Fungi aren't plants and can't produce food by photosynthesis. The hyphae secrete digestive enzymes into the mold’s food source and then absorb the nutrients that are released by the digestion. Molds don’t produce mushrooms, but they do produce sacs containing reproductive spores. The fungi are not always harmful. Some are even useful. Penicillium chrysogenum (originally known as Penicillium notatum), which produces the antibiotic penicillin, is a mold. Some molds produce toxins, however. Toxins produced by fungi are known as mycotoxins.

Aspergillus spores
Credit: Medmyco, via Wikimedia Commons, CC BY-SA 4.0 License


Aflatoxins and Their Effects

WHO (World Health Organization) says that there are “14 or more” types of aflatoxins in nature but that four of them create most of the problems for humans. Two types are found in milk as a result of cows being fed contaminated grain.

WHO classifies aflatoxins as carcinogens (factors that cause cancer). The organization also says that chronic (long term) exposure is needed to see this effect. In addition, they say that the chemicals are mutagenic, which means they can change our DNA. The DNA molecules contain the genes that give us many of our characteristics. Aflatoxins can also cause birth defects. Furthermore, they can cause immunosuppression, or the suppression of our immune system. This system fights pathogens and infections.

WHO classifies all of the above effects as ones that may appear after long-term exposure to the toxins. The organization also describes some effects of acute (short term) exposure to the chemicals. They say that the chemicals can cause serious liver damage that may be fatal. The condition is known as aflatoxicosis. One symptom of the disease is jaundice, which is a yellow colour to the skin and the whites of the eyes. It’s caused by the buildup of bilirubin, a yellow chemical produced by the break down of the hemoglobin in old red blood cells when they're destroyed. Normally, the liver processes the bilirubin, but a damaged liver may be unable to do this. Nausea and tiredness may be other symptoms of aflatoxicosis. Cows, pigs, and chickens can also experience liver damage as a result of alflatoxin poisoning. They obtain the toxin in their food.

Holstein Cows
Public domain image


Effects of Dietary Clay on Aflatoxins in Cows

A recent study from the University of Illinois has discovered that clay in the diet of cows absorbs aflatoxin in the animal's gut and prevents it from being absorbed into the bloodstream. The discovery may help to reduce the aflatoxin level in the milk that people drink.

The researchers used sixteen lactating Holstein cows as their subjects. The cows were divided into four groups as follows.
  • The first group was not exposed to aflatoxin and not fed clay. 
  • The second was given aflatoxins and no clay.
  • The third was given aflatoxins plus food commonly given to cows as well as aluminosilicate clay.
  • The fourth was given aflatoxins and aluminosilicate clay.

Discoveries including the following:
  • Cows given aflatoxin but no clay developed serious inflammation in their liver.
  • Cows given aflatoxin and clay exhibited much less liver inflammation.
  • As more clay was added to the diet of cows exposed to the toxin, substances in the blood that indicated effective liver function and a good immune response “tended to increase”.
  • A gene associated with protein synthesis (MTOR) was “negatively impacted” by the presence of aflatoxin in the diet.
  • Cows that were fed more clay secreted less aflatoxin into their milk.

Preventing Toxicity

The good news is there are many techniques available to detect the presence of aflatoxins in human food and animal feed. The bad news is that aflatoxins are generally distributed unevenly, so sampling of multiple areas is required. Another problem is that an Aspergillus infection may develop in the field even before a crop is harvested and stored. Helping the crop to resist the infestation is important.

One method that has shown promise in protecting a crop before harvest is the use of strains of Aspergillus flavus that don’t produce aflatoxins. The strains that are used actually grow better than the ones that produce the toxin and out-compete the toxic ones, preventing them from growing. Controlling the temperature, humidity, and aeration of areas where harvested food is stored is also helpful.

Toxicity Prevention Tips for Consumers

Although aflatoxin toxicity is less common in North America than in some parts of the world, it still exists on the continent. It’s therefore advisable that consumers take some steps to avoid problems. For example:
  • Inspect grains, nuts, and seeds before purchase. Don’t buy a product if it appears to be damaged or mouldy.
  • Try to buy crop foods that were harvested as close as possible to your home and that haven’t been transported or stored for a long time.
  • Once products have been bought, store them properly in your home and try to eat them soon.
  • Don’t eat an excessive amount of one type of food. This may not be good nutritionally. In addition, if the food contains aflatoxins it increases the chance of harmful effects.
  • Buy reputable products. For example, when peanut butter is made, aflatoxins that are present are not completely destroyed by roasting (or by any other cooking process). It’s therefore important to start the production process with peanuts that are as free from aflatoxins as possible.

References

Aflatoxin facts from WHO

Aflatoxins and cancer from the National Cancer Institute in the United States

Clay supplements reduce aflatoxin level in cow milk from the EurekAlert news service