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Do almonds contain cyanogenic glycosides?

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4 min read

According to research published by the National Institutes of Health, bitter almonds contain levels of cyanogenic glycosides that are approximately 40 times higher than those found in sweet almonds. This significant difference is the key factor in determining whether almonds contain cyanogenic glycosides and the potential health risks associated with their consumption.

Quick Summary

Both sweet and bitter almonds contain cyanogenic glycosides, but in vastly different quantities. A genetic mutation drastically reduces the level of amygdalin in sweet almonds, making them safe for consumption, while bitter almonds contain high amounts that can release toxic hydrogen cyanide upon digestion.

Key Points

  • Variety is key: Sweet almonds, commonly sold in grocery stores, contain only trace, safe amounts of cyanogenic glycosides due to a genetic mutation.

  • Bitter almonds are toxic: Wild and bitter almonds contain high concentrations of amygdalin, a cyanogenic glycoside that can release toxic hydrogen cyanide when consumed raw.

  • Processing eliminates risk: Heat treatments like boiling, roasting, or baking can significantly reduce or eliminate the cyanide content in almonds and other cyanogenic foods.

  • Taste is a warning sign: A distinctly bitter flavor indicates the presence of high levels of amygdalin and suggests the almond should not be eaten.

  • Toxicity occurs upon digestion: Cyanide is released when the almond tissue is damaged, allowing the amygdalin to mix with the enzyme $\beta$-glucosidase during chewing or digestion.

  • Accidental poisoning is rare but possible: Instances of poisoning, though infrequent, can occur from misidentified or mislabeled bitter almonds.

  • Commercial products are safe: Products like almond extract or marzipan made from bitter almonds undergo processing to remove the cyanide, making them safe for consumption.

In This Article

The Core Difference Between Sweet and Bitter Almonds

The fundamental distinction regarding cyanogenic glycosides in almonds lies in the variety. The almonds commonly purchased in grocery stores are 'sweet almonds' ($Prunus dulcis$). These are safe for consumption because they contain only trace amounts of the cyanogenic glycoside amygdalin. This low level is the result of a genetic mutation that occurred thousands of years ago during the almond's domestication process. The defensive mechanism that would normally produce significant amounts of cyanide has been largely 'turned off'.

In contrast, 'bitter almonds' ($Prunus amygdalus$) naturally contain high concentrations of amygdalin. When these raw nuts are crushed or chewed, the amygdalin interacts with an enzyme called $\beta$-glucosidase, which breaks it down to release toxic hydrogen cyanide (HCN) along with benzaldehyde, the chemical compound responsible for the almonds' characteristic bitter taste. For this reason, raw bitter almonds are considered poisonous and are not sold for consumption in many countries, including the United States.

How Cyanogenic Glycosides Release Cyanide

Cyanogenic glycosides are not toxic in their stable form within the plant. The toxic reaction is triggered when the cellular structure of the plant material is disrupted, allowing the glycoside and the hydrolyzing enzyme to mix. This happens automatically when the nuts are chewed, blended, or macerated. The hydrolysis process results in the breakdown of amygdalin into glucose, benzaldehyde, and highly toxic hydrogen cyanide. The body's ability to detoxify small amounts of cyanide can be overwhelmed by consuming too many bitter almonds.

Health Implications and Processing

Consuming raw bitter almonds can lead to serious health issues, with symptoms ranging from nausea and headaches to more severe complications like confusion, breathing difficulties, and seizures. Ingesting a large number of bitter almonds can even be fatal. For adults, eating 50 bitter almonds can be deadly, while as few as 5 to 10 can be fatal for a child.

However, it is possible to reduce or eliminate the cyanide content in bitter almonds through processing. Studies show that heat processing methods can significantly decrease the toxin content: boiling can reduce it by 98%, microwaving by 87%, and baking by 79%. This is why bitter almond extracts and flavoring agents, like those used in commercial almond syrups, contain negligible amounts of cyanide because the processing removes the toxic components.

Comparison Table: Sweet vs. Bitter Almonds

Feature Sweet Almonds ($Prunus dulcis$) Bitter Almonds ($Prunus amygdalus$)
Cyanogenic Glycoside Content Contains trace amounts of amygdalin due to a genetic mutation. Contains high levels of amygdalin naturally.
Toxicity Safe to consume raw in typical serving sizes. Raw nuts are poisonous and should not be consumed.
Flavor Mild, sweet, and nutty. Strong, bitter flavor.
Commercial Availability Widely available in supermarkets, often labeled simply as "almonds". Not typically sold in retail stores in the US; sometimes available in specialty or online markets.
Use Eaten as a snack, used in cooking, baking, and for almond milk. Primarily used for processed flavorings and extracts after cyanide removal.

Sourcing and Avoiding Contamination

While most sweet almonds on the market are safe, there have been rare instances of mislabeling or contamination. In 2014, some raw almonds imported from Spain and Italy were recalled by a major retailer because they were actually bitter varieties. Consumers can mitigate this risk by purchasing US-grown almonds and being mindful of any intensely bitter flavor, which is a strong indicator of a bitter almond. The presence of a bitter taste is the plant's natural warning sign.

Conclusion

In conclusion, the question of whether almonds contain cyanogenic glycosides depends entirely on the type of almond. Sweet almonds, the variety sold for consumption in grocery stores, contain only trace, non-toxic amounts. The danger lies in bitter almonds, which are not typically sold for direct consumption but possess high levels of the compound amygdalin, which breaks down into toxic hydrogen cyanide. For the average consumer, sticking to sweet almonds and being aware of the distinctively bitter taste of a misidentified nut is the simplest way to ensure safety.

Sources

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Frequently Asked Questions

No, not all almonds are safe to eat. Sweet almonds, the kind found in grocery stores, are safe because they contain very low levels of cyanogenic glycosides. However, bitter almonds contain high, toxic levels and are considered poisonous when raw.

The poisonous substance is hydrogen cyanide (HCN), which is released when the cyanogenic glycoside amygdalin, found in high concentrations in bitter almonds, breaks down during chewing or digestion.

The main indicator is taste. Sweet almonds have a mild, nutty flavor, while bitter almonds have a strong, harsh taste. If you encounter an almond that tastes very bitter, it should not be consumed.

Sweet almonds aren't poisonous because a genetic mutation has prevented them from producing high levels of amygdalin, the compound that breaks down into toxic cyanide. They only contain safe, trace amounts.

Yes, heat processing methods like cooking, roasting, or boiling can significantly reduce or eliminate the cyanide content in cyanogenic foods, including bitter almonds. This is why processed products are safe.

If you eat a bitter almond, a few nuts are unlikely to cause serious harm to a healthy adult due to the body's natural detoxification mechanisms. However, symptoms of mild poisoning can include dizziness, headache, nausea, or vomiting. Ingesting more than a handful can be dangerous and requires immediate medical attention.

Bitter almonds can be used for extracts and marzipan, but only after proper industrial processing to remove the cyanide. Do not attempt to use raw bitter almonds in homemade recipes, as they are toxic.

References

  1. 1
    Potential Toxic Levels of Cyanide in Almonds (Prunus Amygdalus), Apricot Kernels (Prunus Armeniaca), and Almond Syrup
  2. 2
    Cyanide and Amygdalin as Indicators of the Presence of Bitter Almonds in Imported Raw Almonds
  3. 3
    Are Almonds Poisonous? Different Varieties Explained
  4. 4
    CYANOGENIC GLYCOSIDES - INFORMATION SHEET
  5. 5
    A Review of Cyanogenic Glycosides in Edible Plants

Related Topics:

#food safety #Almonds #Cyanide #amygdalin #bitter almonds #sweet almonds #cyanogenic glycosides #Toxins in Food

Medical Disclaimer

This content is for informational purposes only and should not replace professional medical advice.