Cyanide Poisoning and Cassava (2024)

Cyanide Poisoning and Cassava (1)

Food Safety Focus (19th Issue, February 2008) – Incident in Focus

Cyanide Poisoning and Cassava

Reported by Ms. Joey KWOK, Scientific Officer,
Risk Communication Section, Centre for Food Safety

Background

On 14 January 2008, the Centre for Food Safety (CFS) advised members of the public to avoid consuming Piranha brand crackers and snacks manufactured by Tixana Australia Pty Ltd. The appeal was made following a warning issued by the Food Standards Australia New Zealand (FSANZ) due to the higher-than-usual levels of naturally occurring cyanogenic glycosides in the ingredient cassava in a batch of exported vegetable crackers. The CFS contacted the relevant authorities and was informed that the affected products had been exported to Hong Kong. The CFS alerted the trade to stop selling the affected products.

What are Cyanogenic Glycosides?

Cyanogenic glycosides are a group of chemical compounds which occur naturally in over 2 000 plant species. There are at least 25 cyanogenic glycosides known to be found in the edible parts of plants. Cyanogenic glycosides alone are relatively non-toxic. However, as a result of enzymatic hydrolysis by beta-glucosidase following maceration of plant tissues as they are eaten, or by the gut microflora, cyanogenic glycosides are broken down to release hydrogen cyanide which is toxic to both animals and humans. The potential toxicity of a cyanogenic plant depends primarily on its capacity to produce hydrogen cyanide.

What are the Symptoms of Cyanide Poisoning?

In humans, the clinical signs of acute cyanide intoxication include rapid respiration, drop in blood pressure, rapid pulse, dizziness, headache, stomach pain, vomiting, diarrhoea, mental confusion, twitching and convulsions. Death due to cyanide poisoning can occur when the cyanide level exceeds the limit an individual is able to detoxify. The acute lethal dose of hydrogen cyanide for humans is reported to be 0.5 to 3.5 mg per kilogram of body weight. Children are particularly at risk because of their smaller body size.

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.

What is Cassava? What is it Used for?

The roots of cassava are rich in carbohydrates, mainly starch. According to Food and Agriculture Organization, cassava is the third most important source of calories in the tropics, after rice and corn. Cassava is consumed in a variety of ways, including eaten as whole root, grated root or root chips. In addition, it is prepared into flour which in turn can be used for cooking or production of cassava-based products such as breads, crackers, and puddings or beverages made with tapioca pearls. Cassava leaves are also eaten in some countries following extensive boiling. Apart from being used as human food, cassava products are also used as animal feed.

Illustration: Cassava

Cyanide Poisoning and Cassava (4)

Illustration: Pearl milk tea drink with tapioca pearls

Cyanide Poisoning and Cassava (5)

How should Cassava be Processed to Render it Safe for Consumption?

Cassava contains more than one form of cyanogenic glycosides. Different varieties of cassava are generally classified into two main types: sweet cassava and bitter cassava. Sweet cassava roots contain less than 50 mg per kilogram hydrogen cyanide on fresh weight basis, whereas that of the bitter variety may contain up to 400 mg per kilogram.

Sweet cassava roots can generally be made safe to eat by peeling and thorough cooking. However, bitter cassava roots require more extensive processing. 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. Cutting the roots into small pieces, followed by soaking and boiling in water is particularly effective in reducing the cyanide content in cassava. Whilst fresh cassava requires traditional methods to reduce its toxicity, adequately processed cassava flour and cassava-based products have very low cyanide contents and are considered safe to use.

What Other Edible Plants Contain Cyanogenic Glycosides?

Bamboo shoot is a popular food item among Asian population. The cyanogenic glycoside present in bamboo shoot is decomposed quickly in boiling water. Other edible plants containing cyanogenic glycosides include kernels within the pits of some stone fruits (e.g. bitter apricot kernels), lima beans, etc.

Illustration: Bamboo shoot

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Advice to Consumers

  1. Buy food from reliable suppliers.
  2. Prepare cyanogenic plants such as cassava and bamboo shoot properly before consumption. Cyanogenic plants should be cut into smaller pieces, soaked in water and cooked thoroughly in boiling water.
  3. Maintain a balanced diet to avoid excessive exposure to harmful chemicals from a small range of food items.

Advice to the Trade

  1. Source food and ingredients from reliable sources.
  2. Adhere to the Good Manufacturing Practice to minimise the risk of natural toxins in food.

Further Information

Further information about natural toxins can be obtained from the following webpages:

  1. CFS Risk Assessment Study Report on Natural Toxins in Food Plants
  2. CFS Risk in Brief on Naturally Occurring Toxins in Vegetables and Fruits
Cyanide Poisoning and Cassava (2024)

FAQs

What is cyanide poisoning in cassava? ›

Cassava roots and leaves cannot be consumed as they contain two cyanogenic glycosides - linamarin and lotaustralin. They are decomposed by linamarase, a naturally occurring enzyme in Cassava, liberating hydrogen cyanide (HCN).

How long to cook cassava to remove cyanide? ›

Boiling/Cooking

As with soaking, the free cyanide of cassava chips is rapidly lost in boiling water. 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).

How do you remove cyanide from cassava? ›

Drying is the most ubiquitous processing operation in many tropical countries. Sun drying eliminates more cyanide than oven drying because of the prolonged contact time between linamarase and the glucosides in sun drying. Soaking followed by boiling is better than soaking or boiling alone in removing cyanide.

What must be removed from cassava to make it safe to eat? ›

Food products: There are hydrocyanic glucosides (HCN) in all parts of the plant; these glucosides are removed by peeling the roots and boiling in water.

Can cassava make you sick? ›

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.

Do all cassavas have cyanide? ›

Different varieties of cassava are generally classified into two main types: sweet cassava and bitter cassava. Sweet cassava roots contain less than 50 mg per kilogram hydrogen cyanide on fresh weight basis, whereas that of the bitter variety may contain up to 400 mg per kilogram.

Can cyanide be destroyed by cooking? ›

Cutting cyanogenic food plants into small pieces and cooking them in boiling water reduced cyanide contents of the food commodities by over 90%. Dry heat could not reduce cyanide contents effectively and only reduced around 10% of the cyanide contents in flaxseeds following oven-heating for 15 minutes.

How do you know if cassava is safe to eat? ›

Is cassava toxic? 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.

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.

Is grated cassava safe to eat? ›

It's important to note is that you must cook cassava root before eating it, as it can be poisonous if consumed raw. Cassava is a versatile root vegetable that's widely consumed in several parts of the world. It's also what tapioca starch is made from. You must cook it before eating it, as the raw form can be poisonous.

What cancels cyanide? ›

Often patients are given oxygen. Two antidotes (sodium nitrite and sodium thiosulfate) are usually used to stop the effects of serious cyanide poisoning. Other drugs may be necessary to control additional health effects of cyanide such as seizures.

What kills cyanide? ›

The United States standard cyanide antidote kit first uses a small inhaled dose of amyl nitrite, followed by intravenous sodium nitrite, followed by intravenous sodium thiosulfate. Hydroxocobalamin was approved for use in the US in late 2006 and is available in Cyanokit antidote kits.

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.

Does boiling water remove cyanide? ›

It's heat plus water that wipes out the cyanide. Boiling for just five minutes can wipe it out, like when making hot cereal or something.

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.

How fast is cassava poisoning? ›

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

How do you identify hydrogen cyanide in cassava? ›

A simple picrate method was used to quantify the cyanide contents of food samples. The cyanide in the food samples reacted with hot 20% HCl solution to produce hydrogen cyanide vapour which reacted with alkaline picrate test strips to form red colour on the test strips.

Are cassava chips safe to eat? ›

Cassava contains the naturally occurring glycoside compound. Correct preparation of cassava eliminates the compound, ensuring products with cassava are safe. If not prepared correctly however, remaining cyanogenic glycoside can trigger cyanide to be made in the gut. This can be a health risk, especially for children.

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