Cassava and the problem of cyanide poisoning (2024)

Cassava is a crop very rich in starch, but it can also be the source of one of the most potent poisons: hydrogen cyanide.

Cassava (Manihot esculenta) is a perennial plant native to South America. It is the third largest energy source for humans, just behind corn and rice, globally.

Of course, it holds a higher position in certain parts of Africa and Asia, where more than half a billion people rely on cassava for their daily energy intake. The top-producing countries are Nigeria and Thailand, followed by Brazil, Indonesia and Ghana. Cassava production continues to expand in Asia and Africa, and also in Latin America. This is not only because of increasing demand as an energy staple, but also because of increasing demand for animal feed, industrial starch uses, and as a substrate for bioethanol production. After all, cassava contains more than 70% starch, making it a very rich source of energy.

Why isn’t cassava used more in animal feed?

The cassava plant produces three main products: tuber chips (flesh), tuber peels and leaves. The peels and leaves contain more fiber and protein, but it is the flesh of the tuber that contains the most important commodity: the starch. We shall focus on the cassava chips, which are the most industrially available for the moment.

The main problem of raw cassava tubers is their high concentration of cyanogenic glucosides (with peels containing more than the flesh). These compounds exist as a natural defense mechanism for the plant and they become activated once the tissue becomes damaged. The main cyanogenic glycoside of cassava is linamarin (the same as in linseed) making up more than 90% of total such compounds in the tuber. Once linamarin is activated by the enzyme beta-glucosidase, it releases prussic acid (hydrogen cyanide, HCN) which is a highly volatile substance characterized by the odor of bitter almonds. It is highly toxic to animals when consumed at high enough quantities, causing asphyxia and death. At lower levels, it can be detoxified internally by the enzyme rhodanase into thiocyanate (sulphur-nitrogen containing compound) provided that there is adequate methionine available to function as a sulfur donor. Thiocyanate, although less toxic, can also cause enough problems as it is a potent goitrogen, such as in the case of glycosinolates in rapeseed meal.

To prevent humans and animals from becoming poisoned, raw cassava tubers are first peeled and the flesh is sliced or shred. The resulting “chips” are sun dried (most often used method when destined for animal feed) long enough to allow the volatile prussic acid to evaporate. Complete removal is impossible, but a reduction of at least 90% is considered sufficient for animal feeding. The flesh of sweet cassava varieties contains low levels of hydrogen cyanide (less than 50 mg/kg hydrogen cyanide), but bitter varieties are rather rich (over 200 mg/kg), with certain ones containing more than 1,000 mg/kg. Therefore, knowing the initial variety is important as 90% reduction of 50 mg/kg is substantially different compared to 90% reduction of 200 mg/kg.

Testing is key to correct usage

Testing processed cassava chips is a must before feeding them to all animals, and there are easy and quick methods that can be used for field tests, to be followed by more accurate laboratory tests. Sampling is not to be taken lightly as incorrect procedures will lead to incorrect results, with possible catastrophic repercussions. Not properly testing for hydrogen cyanide content has been the major reason why cassava chips are considered by many feed professionals as questionable for animal feeding. In reality, however, cassava chips low enough in hydrogen cyanide can be used to completely replace all cereals, especially in monogastric animals. This does not apply to ruminants as the rumen microbes can hydrolyze any remaining glucosides releasing thus even more hydrogen cyanide. In practice, however, cassava chips are used to replace only a portion of cereals, depending on hydrogen cyanide concentration (if known) or their origin (if unknown).

Cassava and the problem of cyanide poisoning (2024)

FAQs

Cassava and the problem of cyanide poisoning? ›

Chronic cyanide intoxication may lead to the development of certain conditions including disturbance of thyroid function and neurological disorders. It tends to affect those individuals who have regular long-term consumption of cassava with poor nutrition status.

Is it safe to eat cassava with black lines? ›

The interior flesh should be white. Avoid roots with cracks, mold, soft spots, or sour smell. The flesh will have black specks, lines, or discoloration. If you do buy cassava with some black streaks hiding within the flesh, you can cut them out and use what remains.

Does cooking remove cyanide from cassava? ›

The best processing method for the use of cassava leaves as human food is pounding the leaves and cooking the mash in water. Fermentation, boiling, and ensiling are efficient techniques for removing cyanide from cassava peels.

What is the main cause of cassava poisoning? ›

Cassava, an edible tuberous root often made into flour, contains cyanogenic glycosides, which can result in fatal cyanide poisoning if not properly detoxified by soaking, drying, and scraping before being consumed. Acute cassava-associated cyanide poisoning outbreaks are rarely described.

What is the problem of cyanide in cassava? ›

People should not eat cassava raw, because it contains naturally occurring forms of cyanide, which are toxic to ingest. Soaking and cooking cassava makes these compounds harmless. Eating raw or incorrectly prepared cassava can lead to severe side effects.

Who should not eat cassava? ›

Nutrition of Cassava

However, it's a good source of potassium, folate, vitamin C, and several other nutrients. Though this doesn't make cassava unhealthy, people following low-carb diets and people with blood sugar regulation issues, such as those with type 2 diabetes, should avoid consuming large amounts of cassava.

How is toxin removed from cassava? ›

One of the traditional ways to prepare bitter cassava roots is by first peeling and grating the roots, and then prolonged soaking of the gratings in water to allow leaching and fermentation to take place, followed by thorough cooking to release the volatile hydrogen cyanide gas.

How to avoid cassava poisoning? ›

Based on this characteristic of cassava, if you know how to process it properly, the toxic content will be eliminated to a large extent. After being peeled, soaked in water for a while, boiled and cooled, the toxic content is reduced to only 30% of the original.

Which is healthier, potato or cassava? ›

However edible varieties of cassava and potatoes grown for consumption are low on toxicity. Cassava is more healthier if you can eat the green leaves which are edible after blanching/boiling and straining and contain useful amounts of amino acids/proteins.

What happens if you eat too much cassava? ›

Cassava that is prepared improperly can contain chemicals that are converted to cyanide in the body. This may cause cyanide poisoning and lead to certain paralysis conditions. This is especially true if eaten as part of a low-protein diet. In some people, eating cassava can cause an allergic reaction.

How fast is cassava poisoning? ›

Symptoms of cassava poisoning usually appear after eating about 3-7 hours.

How to properly prepare cassava? ›

Here is how to prepare cassava safely:
  1. Step 1: Soak and Peel. "It is essential to peel, soak,5and cook in order to remove any toxins," says Shapiro. ...
  2. Step 2: Boil. Next, bring a pot of water to a boil. ...
  3. Step 3: Choose Cooking Method. Cassava can be consumed in many ways.
Mar 8, 2024

Does cooking destroy cyanide in cassava? ›

Boiling/Cooking

About 90% of free cyanide is removed within 15 minutes of boiling fresh cassava chips, compared to a 55% reduction in bound cyanide after 25 minutes (Cooke and Maduagwu, 1978). Cooking destroys the enzyme linamarase at about 72°C thus leaving a considerable portion of the glucoside intact.

How do you remove cyanide from cassava? ›

The traditional method for removing cyanogens from pounded cassava leaves is by boiling in water which removed all cyanogens in 10 min.

What does cassava do to the brain? ›

Various animal studies on neurotoxicity due to cassava reported decreases in motor coordination and neurotransmitter changes, particularly dopaminergic changes in the brain (Mathangi et al., 1999; Mathangi and Namasivayam, 2000) .

How can you tell if cassava has gone bad? ›

When cassava is spoiled, the first thing you'll notice is changes in color. Its flesh will start to appear yellow or develop dark areas. An off odor, which is pretty strong and unpleasant, may also be noticeable.

Why does cassava turn black? ›

Good cassava will be white inside and the spoilt one will be black. Cassava should never be eaten raw as it contains harmful toxins that are concentrated on the outer layer of the cassava skin. You must peel it properly and remove the brown part before you turn it in to your preferred preparation.

What is the black rot in cassava? ›

Typical symptoms of BSRR disease were vascular discoloration, offensive odor, blackening, decaying of the stem, and rotting of roots. Small-sized black pycnidia and dieback symptoms were also observed on the diseased cassava stems and stalks.

Can you eat yucca with black spots? ›

If the flesh has black specks, lines, or any discoloration, it should be discarded. Rotten or decaying yuca has soft brown spots and a putrid smell. You can also find frozen peeled and cut yuca. Unpeeled cassava should be stored in a cool, dry place like the pantry, where it will last one week.

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