From roots to leaves, cassava can be processed and combined with wheat, sorghum or millet to make various products such as flour, chips, bread, crisps, chapatti and biscuits for sale.
Cassava is the third most important source of carbohydrates in Africa and the second most important food crop after maize in the Western and Coastal regions of Kenya. Cassava provides over 500 calories daily making it an important food security crop.
Nutritional value
Cassava has a high calorific value of 160 calories in 100g. The young tender cassava leaves are rich in proteins, fibre and vitamin K which is important in helping blood clot. It has vitamin A, which is important for normal vision, boosts the immune system, and reproduction and B1, also called thiamine or thiamin and it helps the body to convert carbohydrates into glucose, which the body uses to produce energy and helps metabolize fats and protein.
Cassava tuber is rich in the B-complex group of vitamins such as folates, thiamin, pyridoxine (vitamin B-6), riboflavin, and pantothenic acid. It is a good source of some essential minerals such as zinc needed for the body’s defensive system to work properly. It plays a role in cell division, cell growth, wound healing, the breakdown of carbohydrates and for the senses of smell and taste. The magnesium in cassava also helps to maintain normal nerve and muscle function, supports a healthy immune system, keeps the heart beat steady, and helps bones remain strong. The copper in the tuber works with iron to help the body form red blood cells, helps keep the blood vessels, nerves, immune system, and bones healthy. Iron is found in haemoglobin which is essential for transferring oxygen in your blood from the lungs to the tissues. It contains manganese that helps the body form connective tissue, bones, blood clotting factors, and sex hormones.
It plays a role in fat and carbohydrate metabolism and blood sugar regulation and potassium, which is crucial to heart function and plays a key role in skeletal and smooth muscle contraction, making it important for normal digestive and muscular function.
However, cassava has a poisonous compound in the class of cyanogenic glycoside known as linamarin (96%) and lotaustralin (4%). These compounds are distributed largely in the leaves and the root cortex (skin layer) with smaller amounts in the root parenchyma (interior).
Tuber injury releases linamarase which changes linamarin to hydrocyanic acid (HCN) which is responsible for cyanide poisoning after cassava consumption (do not throw cassava tubers when harvesting or handling it to prevent injury to the skin).
Cassava processing techniques to reduce cyanide level
The initial cyanide level in cassava determines the safety of the product in relation to the processing method adopted. According to Food and Agricultural Organization/World Health Organization up to 10 mg Hydrogen Cyanide (HCN) equivalent to one kilogram of flour is attained, if the initial cyanide level of roots does not exceed 200 mg/kg.
a) Soaking, storage and boiling: Soaking the tuber for three days followed by boiling in salt-vinegar water results in complete evaporation of HCN. Studies report that cyanide levels drop by about 30% after four days of cassava storage at ambient temperature, 50% after boiling, 80% loss when grated and boiled, and 50% when grated and cooked in an earth oven.
b) Fermentation: Yeast can utilize cyanogenic glucoside and their metabolites, thereby reducing toxicity (poisonous compounds). Studies have shown that a combination of yeast and lactic acid bacteria is most effective than using any of the organisms alone in fermentation. Traditional fermentation takes up to 6 days.
c) Grinding and drying: Grinding exposes the linamarase enzyme that converts the toxic compounds in the roots into volatile compounds. Sun-drying the product to lower moisture content yields a product of low cyanohydrin content. However, prolonged sun-drying alone will not reduce cyanogenic compounds in bitter cassava roots to the safe limit set by FAO. Therefore, combination processing (drying and then grinding) is most effective.
Value addition of cassava Cassava composite flours
After detoxification, cassava root tubers can be dried under the sun to obtain a low moisture content and then ground or milled to obtain flour. This flour can be used in combination with other flours such as millet, wheat, sorghum and others to make what is called composite flour fortified to improve the nutritional profile of the product.
Mixing ratio is determined by an individual’s nutritional needs calculated through mass balancing by food processors. Composite cassava flours are used to make bread, pastries, cookies, biscuits, chapati and other flour based products.
Cassava chips: Detoxification is the first step before further processing. Peel the cassava and cut into long strips of 6mm thickness. Boil the cassava for 15 minutes. Deep fry in hot oil until golden brown.
Cassava crisps: Preparation is like that of the chips. However, slice the cassava into very thin slices and cook in hot frying oil until crispy brown. Package in polythene bags.
Dried cassava leaves powder: Boil the cassava leaves for 15 minutes to reduce the cyanide content. Dry under the sun in solar driers for 12 hours depending on the weather conditions or in a hot air oven at commercial scale. Dry until the moisture content is below 7%. Grind the leaves and pack in well- labelled bags.
Animal feeds: Cassava peels can be used as animal feeds or recycled as fertilizer.
This article first appeared on TOF magazine distributed under the terms of the Creative Commons Attribution License(http://creativecommons.org/licenses/by/2.0)
Also read: Cassava Planting Guide