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Aflatoxins in Nuts and Dried Fruits: Danger or Hype?

Aflatoxins in Nuts and Dried Fruits: Danger or Hype?

We have heard a lot about the benefits of nuts and dried fruits. Nuts are heart-healthy foods, and dried fruits also carry the benefits of their former selves.  Many people rely on them for a healthy and reliable source of food ingredients.  However, some consumers worry about the presence of Aflatoxins in them. 

Don’t worry! We do not mean to frighten you but to help you avoid this life-threatening substance.

In this article, we will take a closer look at the contamination of aflatoxins in nuts and dried fruits. We will introduce the risk of aflatoxin poisoning, and summarize detoxification methods. We also highlight market regulations for aflatoxin avoidance.


What are Aflatoxins?

Aflatoxins are a family of life-threatening toxins produced by certain fungi. The fungi can contaminate crops in the field, at harvest, and during storage. Maize (corn), peanuts, cottonseed, and tree nuts are frequently contaminated by these toxins.

The picture shows structures of Aspergillus flavus, one of the fungi that produce aflatoxins in crops.
Aspergillus flavus a major producer of aflatoxin in nuts and dried fruits

Types of Aflatoxins in Nuts and Dried Fruits

There are more than 14 types of Aflatoxins in the world. However, only four types are dangerous to humans and animals, referred to as B1, B2, G1, and G2. Aflatoxins-producing fungi mostly grow in warm and humid climates, the type of climate needed by most nuts. Sometimes the drought, insect damage, and poor storage may help the growth of this toxin in different foods. That also happens in regions with high temperatures during storage.

Country officials check nuts and dried fruits for these types of aflatoxins before entering the market. But that doesn’t mean Aflatoxin contamination should be zero. The maximum acceptable level of aflatoxins in nuts and dried fruits usually is 20 parts per billion (ppb), which is below the dangerous level. Some nuts and dried fruits should have even lower aflatoxin levels than the mentioned number to be accepted in the market.

Aflatoxins in Nuts

Aflatoxins in Nuts and Dried Fruits: Danger or Hype? | Aflatoxins in Nuts

Aflatoxins in Peanuts

Generally, peanuts top the list of aflatoxin contamination. One kilogram of peanuts should contain only 4 ppb (4 mcg/kg) of total aflatoxin and 2 ppb of aflatoxin B1.

Aflatoxin in peanuts is a major concern but you can easily avoid them by visually checking the nuts. The moldy, discolored parts on nuts may be a sign of fungus colonization on the fruits. Look for these signs on peanuts and avoid buying those infected to reduce the risk of exposure to aflatoxins.

Try to buy high-quality peanuts from the market and make your peanut butter at home. Also, remember to store the fruits in a dark and cool place to prevent them from rotting. Any discoloration on peanuts should be seen as a sign of fungus contamination.

American pistachio

Aflatoxins in Pistachio

After peanuts, pistachios are at high risk of contamination by aflatoxin B1. Pistachios growing in good conditions have the highest quality and are less prone to infection by aflatoxins.

The acceptable level of aflatoxins in pistachios is 10 ppb of total aflatoxins and 8 ppb of aflatoxin B1. It is the most dangerous type of aflatoxin. The FDA and European Commission have placed separate limitations on it.

Pistachio wholesalers should always try to source this expensive nut from well-known suppliers. They should also keep their inventory in cool and dry places to avoid any mold or infection. Customers need to make their purchases from popular shops on the market. You can tell if pistachios are infected by checking the color of their shells and kernels.

Aflatoxin contamination can affect raw vs roasted pistachios but rarely affects pistachio kernels. It mostly affects their color. Any discoloration on pistachio nuts or pistachio kernels may show aflatoxin infection.

Brazil Nuts

Aflatoxins in Brazil Nuts

Despite their many health benefits, Brazil nuts are susceptible to aflatoxins infection. It may negate some of the beneficial effects of selenium in this nut. Selenium can help the body become more resistant to different types of cancer, and Brazil nuts are high in this substance.

To ensure you are consuming aflatoxin-free Brazil nuts, look for undamaged ones. Like other nuts, any discoloration or mold-looking part on Brazil nuts can be aflatoxin contamination.

Studies show that in-shell Brazil nuts might have lower levels of aflatoxins than the shelled ones.

Cashe

Aflatoxins in Cashews

Research on nuts shows that aflatoxin contamination is less likely to develop in cashews than in other nuts. But, it doesn’t mean that the amount of aflatoxins in cashew nuts is zero.  It is much lower than other nuts, including Brazil nuts, walnuts, peanuts, or pistachios.

You still need to buy high-quality cashews without any damage or discolorations. One kilogram of cashew nuts can contain a maximum of 4 ppb of total aflatoxins and 2 ppb of aflatoxin B1.

Aflatoxins in Dried Fruits

Dried fruits can also be contaminated with aflatoxins. Studies have confirmed aflatoxins in dried plums (prunes), dates, and raisins, but it can be a major concern in dried figs.

dried figs

Aflatoxin in Figs

Fig is a highly perishable fruit. Drying is a reliable method to preserve both the physical and nutritional quality of these delicious fruits. However, aflatoxin contamination can affect the quality of figs in bad storage conditions. This happens commonly where natural sun-drying methods are still practiced. 

The aflatoxins incidence is high in dried figs. The maximum limits for aflatoxin contamination in figs of the European Union are 6 µg/kg AFB1 and 10 µg/kg total aflatoxins. 

Dried figs are usually inspected under ultraviolet light to determine their aflatoxin infection. The bright greenish-yellow fluorescence you see could be aflatoxin contamination (Ömer Barış Özlüoymak, 2014).

The picture shows aflatoxin formation on dried figs detected by ultraviolet light.
Discoloration of dried figs contaminated with aflatoxins.

Figs are susceptible to mycotoxin at any time during processing, storage, and even during fruit retailing. To avoid mycotoxin contamination, the temperature should be above 30 ◦C and close to 37 ◦C during the drying process. Temperatures below 10 ◦C are recommended for industry processing, storing, and retailing dried figs.

Aflatoxin Potential Dangers for Human

Doses of aflatoxins beyond the acceptable levels are dangerous and may lead to the following problems:

  • Poisoning, also called Aflatoxicosis, is a life-threatening illness.
  • Liver damage, or liver cancer, especially for people who may have conditions such as Hepatitis B infection.
  • Vomiting and abdominal pain, as early side effects of consuming high doses of aflatoxins.
  • Some people might even go into a coma if they consume a high amount of aflatoxins.

How to Minimize the Risks of Aflatoxins in nuts and dried fruits?

Minimizing the risk of aflatoxins in nuts and dried fruits requires a concerted effort at several levels. First of all, the farmers and companies should check their food crops and keep them safe from the impacts of fungi. But can’t completely remove this substance from our food chain.

The Food officials (e.g., the FDA in the US) also have considered a maximum acceptable amount of aflatoxins in nuts and dried fruits. This is to ensure they are not harmful to the human body. There are still things to be done on the consumer’s part to avoid aflatoxins contamination if other measures fail:

  • Buy nuts and dried fruits from trusted brands that follow food regulations.
  • Avoid storing nuts and dried fruits in conditions that are propitious to fungal colonization. Moisture, mechanical or insect damage, and temperature can promote contamination and aflatoxin production.
  • Visually inspect the nuts you want to buy for any discoloration or other problems.

How to Detoxify Aflatoxins in Nuts and Dried Fruits?

There are ways to destroy or neutralize aflatoxins in nuts and dried fruits before they are consumed (pre-intake methods). There are also ways to detoxify aflatoxin in the human body after consumption (post-intake methods).

Pre-intake methods

Research has found several ways to remove aflatoxin (especially AFB1) from contaminated foods. These include physical methods, biological methods, and chemical methods

Physical methods include applying heat and gamma rays. Aflatoxins are highly heat-tolerant. Studies have shown that the levels of aflatoxin fall by 41% and 81% when foods are heated at 100 to 150°C, respectively,  for at least 90 minutes.

Biological methods tend to reduce AFB1 levels in contaminated foods using biotechnology.  The biological methods fall into two main categories: The first group uses plant extracts to degrade AFB1.  The other group inoculates bacterial strains in food substrates. The plant extract method has become very popular in recent years because they are safe, effective, and biodegradable. Plant extracts degrade aflatoxins into nontoxic compounds via enzymatic reactions.

Chemical methods use acids, bases, oxidizing agents, and reducing chemicals to destroy aflatoxin. 

Post-intake Methods

There are two general ways to detoxify aflatoxin from the human body. These include aflatoxin adsorption and aflatoxin metabolization. 

The aflatoxin adsorption method uses aflatoxin absorbents that bind to the toxins and stop them from being absorbed by the body.

The aflatoxin metabolization method uses metabolic pathways to break aflatoxin into nontoxic compounds. 


Conclusion

The presence of aflatoxins in nuts and dried fruits poses a threat to human health. Consuming this toxin may lead to different health problems, including liver cancer. But, it is rare for people to be poisoned by aflatoxins because all nuts and dried fruits are strictly controlled before entering the market. Besides, it is relatively easy to determine if nuts and dried fruits have aflatoxin as the toxin normally changes the color. Thus, you may be able to distinguish healthy from unhealthy ones simply by how they look.

Have you ever experienced aflatoxin poisoning? What happened? How did you feel? How did you recover? Please share your experience with us in the comment section.

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