Linamarin is a naturally occurring compound classified as a cyanogenic glycoside. This means it contains a cyanide group that can be released under specific conditions. It is found in the leaves and roots of various plants. When consumed, linamarin has the potential to decompose into hydrogen cyanide, a toxic chemical.
The Mechanism of Toxicity
The toxicity of linamarin arises when it is broken down by the enzyme linamarase. This enzyme is present within the same plant cells as linamarin but is kept separate until the plant tissue is damaged, such as by chewing. When linamarin contacts linamarase, an enzymatic reaction breaks it down into acetone cyanohydrin. Acetone cyanohydrin then spontaneously decomposes, releasing hydrogen cyanide (HCN).
Hydrogen cyanide is a volatile compound that can readily evaporate into the air or dissolve in water. The body’s absorption of linamarin itself is not acutely toxic, as it is rapidly excreted in urine if it remains intact. However, if linamarin breaks down in the gut due to enzymatic activity from gut flora, it can still liberate cyanide, leading to health concerns.
Major Food Sources and Risks
Linamarin is present in various food sources, but cassava (also known as manioc or yuca) is globally the most significant source. This root crop is a staple food for millions, particularly in tropical regions. Other foods that contain linamarin include lima beans, flaxseed, and bamboo shoots.
Consuming foods with high levels of linamarin without proper processing can lead to acute and chronic health issues. Acute poisoning symptoms can include rapid breathing, low blood pressure, dizziness, and collapse, as cyanide interferes with the body’s ability to use oxygen. Long-term exposure to cyanide from insufficiently processed cassava has been linked to neurological disorders, such as konzo, a paralytic disease affecting the upper motor neurons, and tropical ataxic neuropathy. There is also some evidence suggesting a link between dietary exposure to linamarin and glucose intolerance or aggravation of existing diabetes.
Safe Preparation to Eliminate Toxicity
To reduce or eliminate linamarin and its toxic byproducts, various traditional processing methods are employed, especially for cassava. Pounding or crushing cassava roots is highly effective because it ruptures plant cells, bringing linamarin into direct contact with the linamarase enzyme, facilitating the breakdown into cyanide. This mechanical action allows for the subsequent release of volatile hydrogen cyanide.
- Soaking cassava roots in water for several days allows linamarin to leach out and encourages fermentation, aiding detoxification.
- Combining soaking with sun-drying can remove a significant amount of cyanogens (e.g., 97.8% to 98.7% removal reported).
- Fermentation, often followed by roasting (as in gari or farina production), can reduce total cyanogen content by about 98%.
- Boiling thin pieces of cassava can reduce cyanide levels, though heat alone may not completely eliminate linamarin due to its stability at high temperatures.
- For cassava leaves, which have higher cyanogen levels than roots, pounding and boiling can remove approximately 99% of cyanogens.