“Cassava is one of the resilient staple crops that plays a vital role in ensuring food security and nutrition, while at the same time providing by-products for animal feed and bioenergy”
By Elias Biwott
AS CHALLENGES OF harsh climatic conditions characterized by erratic rainfall increase, farmers are gradually embracing farming of resilient and sustainable crops. Cassava is one of the resilient staple crops that plays a vital role in ensuring food security and nutrition, while at the same time providing by-products for animal feed and bioenergy.
Cassava’s remarkable resilience to drought, pests, and diseases makes it well-suited for cultivation in regions where water scarcity and environmental stresses are prevalent. With its adaptations, low external input requirements, and deep root system, cassava efficiently taps into moisture and nutrients stored deep within the soil, enabling it to withstand low fertility, prolonged dry spells, and erratic rainfall patterns.
Cassava also has an economic importance in that, farmers who embrace circular economic principles, such as recycling cassava waste into biodegradable packaging or compost, can further enhance their resilience.
Nutritive value and use
The roots of cassava are rich in carbohydrates, mainly starch. Cassava is consumed in a variety of ways, including eaten as a 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 ugali, bread, crisps, cakes, crackers, puddings or beverages, and production of pharmaceutical beauty products among others.
Apart from being used as human food, cassava products are also used as animal feed if well dried. Cassava is also an important source of raw material for the industries of starch, alcohol, glucose, acetone, glues, paper, stabilizers, etc.
What are Cyanogenic glycosides found in cassava?
Cyanogenic glycosides are a group of chemical compounds which occur naturally in all parts of the plant, but the leaves are more toxic than the roots, the concentration is higher in the central cord and in the bark but are relatively non-toxic alone. The potential toxicity of cyanogenic plants is largely dependent on their ability to produce lethal concentrations of hydrogen cyanide when exposed to humans. In cassava, hydrogen cyanide, which is toxic and poisonous to both animals and humans when ingested. Bitter cassava is more detrimental to one’s health as compared to sweet cassava. Their content varies according to the age of the plant, the variety, environmental conditions, type of soil, climate and pH. Cyanogenic glycosides act as a natural pesticide to protect plants against animal pests.
What are the symptoms of cyanide poisoning?
In humans, the signs and symptoms of acute cyanide intoxication include rapid respiration, drop in blood pressure, rapid pulse, anxiety, dizziness, headache, stomach pain, vomiting, diarrhoea, mental confusion, twitching and convulsions, paralysis and even coma. The effects begin to manifest a few minutes after consumption and poisoning can develop over minutes or hours, and eventually cause immediate death if there is a delay in seeking medical attention.
Other illnesses caused by chronic cyanide intoxication include; diabetes associated with calcification of the pancreas, cancer caused by the formation of carcinogenic nitrosamines in the stomach and an abnormally high incidence of congenial malformations where children are born with imperfection of the limbs.
How should cassava be processed to render it safe for consumption?
The techniques and processes generally used involve sun drying, grinding and grating, pressing, immersion in water, fermentation, roasting or cooking, or usually a combination of these. In these processes the glycosides are eliminated by hydrolysis, freeing the very volatile HCN to be lost in the surrounding atmosphere.
Sun-drying: The roots are peeled, cut in slices or longitudinally and dried in the sun, while the mass is turned occasionally for 2 to 4 days, depending upon the weather conditions. This reduces the cyanide levels in the cassava before preservation or milling into flour.
Grinding and grating: This breaks down the fresh plant tissue, promoting biochemical reactions between the glycosides, and endogenous and exogenous enzymes. The grated cassava should be left long enough. Detoxification depends on the length of time the sample rests, temperature, particle size, and pH.
Immersion and fermentation in water: The immersion helps in the process of detoxification because it breaks the cells by osmosis and some fermentative action, which contributes to glycoside hydrolysis. The product is immersed for 2 to 8 days and then grated or grounded, pressed by hand into small cakes, sun-dried, and finally roasted and milled to produce flour. This product has very good palatability, and digestibility and is completely safe. This process will not be effective if the soaking time is too short.
Reducing cassava cyanide improves cognitive development Even low levels of cyanide exposure over time can cause cognitive impairment that may have lifelong effects, especially among children. Heavy consumption of cassava as a primary food source during most meals or lack of dietary variety can lead to cyanide poisoning, (a paralytic disease) or even death. Children are particularly at risk because of their smaller body size.
How to avoid cassava poisoning?
Even though cassava poisoning is considered highly fatal, if processed and prepared well, all these fatal repercussions can easily be avoided.
Advice to consumers and traders
- Cassava roots should be peeled, cut into small pieces or grated/ ground into flour, soaked in cold water in a basin and let to stand in the shade for five hours or in the sunlight for two hours and then cooked thoroughly in boiling water to reduce the harmful cyanide toxins.
- It is also highly advised to take and maintain a balanced diet to avoid overexposure to hydrogen cyanide present in cassava roots from a small range of food items. Varied diets and access to foods like eggs, dairy, meat and fish that can transform dietary cyanide into more harmless compounds are good.
- Buy cassava food products from reliable suppliers. Prepare cyanogenic plants such as cassava properly before consumption.
- Don’t buy cassava roots in the market and chew them. Avoid eating raw cassava because it has high cyanide levels, which is poisonous and harmful to health.
- Cassava should be harvested as soon as it matures since when it overstays on the farm, it becomes woody and high quantities of cyanide develop.
- Grow low cyanide varieties in order to reduce intake. New and safer varieties developed through plant breeding and the application of biotechnology could make an important contribution.
- Source food and ingredients from reliable sources. Adhere to the Good Manufacturing Practice to minimize the risk of natural toxins in food.
Treatment of cassava poisoning
In the case of cassava poisoning, immediate medical attention is highly advised, as it can be treated if diagnosed early. It is mostly treated by using the cyanide antidote kit which can be found in a hospital. The kit includes three medications (amyl nitrite, sodium nitrite, and sodium thiosulfate) administered together.
The amyl nitrite is given for 15 to 30 seconds, while sodium nitrite is given intravenously over three to five minutes. Intravenous sodium thiosulfate is administered for about 30 minutes. This medication neutralizes hydrogen cyanide in the body by allowing an enzyme called rhodanese to reduce the toxicity of the chemical by catalyzing the conversion of cyanide to thiocyanate. It is also usually accompanied by using an oxygen ventilator.
Even low levels of cyanide exposure over time can cause cognitive impairment that may have lifelong effects especially among children. Heavy consumption of cassava as a primary food source during most meals or lack of dietary variety can lead to cyanide poisoning, or even death. Children are particularly at risk because of their smaller body size.
Elias Biwott is an extension officer at Biovision Africa Trust Farmer Resource Centre at KALRO Kakamega. Email: ebiwott@biovisionafrica.org