Cassava is a woody shrub of the family Euphorbiacea possessing tall, thin, straight stems and when fully grown, attains an average height of 1-2 meters although some cultivars may reach a height of 4 meters. The stem is often marked along its entire length by numerous leaf scars indicating the position from where its palmate leaves of five or six leaflets have dropped off. Depending on the variety and age of the plant, the fibrous roots may be up to 100 centimeters long. Some of these fibrous roots undergo the process of tuberization (swelling due to the cambium tissue) leading to increase in the diameters of the roots.
- Uses of Cassava
- Food(Garri, Fufu)
- Live Stock Feeds,
- Bakery and Confectioneries.
- Modified starch
- Soil and Climatic Conditions Required for Cassava Production
For good growth and yield, cassava requires friable, light textured and well drained soils containing sufficient moisture and a balanced amount of nutrients. Depending on moisture conditions of the soil, farmers plant cassava cuttings vertically, at an angle, or horizontally. It requires Optimal temperature of 25-29 (°C), Optimal rainfall of 100-150 (cm) and an Optimal pH of 5-6.
- Planting Materials
Cassava is vegetatively propagated from stem cutting. The best stems or stakes for planting are obtained from plants that are 10 -12 months old. However, stems can be cut and supplied to farmers or cassava growers from 6 to 7 months old cassava plants. In this situation, the roots are not uprooted. The plants are cut at a height of 20 to 25 cm from the ground level and allowed to regenerate.
Cassava stems are cut in the field into one meter lengths and tied in bundles of 50 sticks per bundle and it is in this form that the stems are sold. There are many cassava varieties under cultivation in Nigeria. They can be distinguished by such morphological characteristics as leaf size, colour and shape, branching habit plant height, colour of stem and petiole, tuber shape and colour, time of maturity and yield.
- Cassava varieties
Cassava varieties are also classified according to the levels of cyanogenic glucosides (hydrocyanic acid, HCN) in the root and leaves. As described earlier, the major groups are:
- Cassava with high HCN level – 100 mg per kilogramme fresh weight or more e.g. TMS 50395.
- . Cassava with intermediate levels of HCN ranging between 50 and 100 mg per kilogramme fresh weight e.g: TMS 30572, TMS 30555
- Cassava with low HCN level – less than 50 mg per kilogramme fresh weight e.g. TMS 4 (2)1425, TMS 30001.
- Cassava Processing
Cassava is processed to reduce moisture content and hydrogen Cyanide levels. A description of some of the most common technologies is as follows.
- Chip Production:
Chip production involves cutting peeled or unpeeled cassava roots into smaller pieces and allowing the pieces to dry. Sun drying is the most common and acceptable drying technique, while different types of chipping machines or choppers are used for cutting the tubers
- Pellet Production:
Production of pellets involves pressing chips and extrusion through a large die. The heat and moisture in the chips help in the formation of pellet like shaped product known as soft pellets. Later process developments involved grinding of chips followed by steam extrusion. This process produces strong pellets upon cooling. These types of pellets are known as hard pellets.
- Cassava Starch and Flour Production:
Starch production involves peeling and washing of the tubers followed by grating or mashing (also called pulverization) and then mixing the resultant mash with water. The suspension is then sieved and the slurry sedimented. Water is decanted and the sedimented starch dried. Flour production involves peeling and washing the tubers. These are then cut into pieces and dried. The dried pieces are then milled and sieved. The resultant flour in this process is the unfermented flour. The fermented flour is produced by fermenting cassava through soaking or steeping the peeled and cut pieces of cassava in water. The fermented pieces are then dried before milling and sieving.
- Modified Cassava Starch Production:
Starch produced by the methods described above is known as’native starch’. Modified cassava starches are produced to serve certain purposes for which native starch is not adequate.
- Acid Modified Starch:
This is obtained by reacting liquid native starch with hydrochloric and sulphuric acids. The process decreases the degree of sickness of starch. It also reduces the temperature required to convert the starch into gel. Acid modified starches are also called hydrolysed starches.
- Oxidized Starch or Hypochlorite Modified Starch:
This is produced by the process of oxidation when the native starch reacts with chloride (e.g. sodium hypochloride) in an alkaline (pH 8-11) medium. The derived starch will become less sticky with the degree of its stickiness depending on the amount of chloride used and the reaction time.
This is obtained when native starch is roasted in a drum under high temperature, while certain acids are sprayed to react with it. Dextrins are of different types namely: yellow dextrin, white dextrin and British gum. Dextrins are used in gumming operations such as glue and adhesives.
- Alpha Starch or Cold-water-soluble Starch:
This is obtained by a process called pregelatinization. In this process, liquid native starch in 40-50% concentration is drum dried. Starch is cooked and dried to form a thin crispy layer, which is latter ground and sifted to obtain fine powder. The fine powder becomes glue immediately on addition of water to it.
- Starch Derivatives:
These are processed starches whose molecular structures have been altered through chemical reactions e.g. starch esters (acetylated starch, phosphoric acid ester) starch ether (carboxymethyl ether and hydroxyethyl starch) and cross linked starch.
- Ethanol Production from Cassava:
Cassava is first transformed to dried chips and the starch in the chips are initially hydrolyzed by liquefying enzymes (i.e. (3-amylase) and saccharifying enzymes (i.e. glucoamylase) to glucose, which is subsequently fermented to ethanol by yeast usually Saccharomyces sp. Recently, simultaneous saccharification and fermentation (SSF) method has been developed for the production of ethanol from cassava chips. In the SSF process, liquefied starch is hydrolyzed to glucose, which is immediately converted to ethanol by yeast at the same production stage. The ethanol produced by either process is recovered through distillation. The amount and quality of ethanol released and recovered depends to a great extent, on the efficiency of the enzymes used, the management of each stage, and the sophistication of the equipment used at each stage of the production process.
process of flour production is described fc
Ethanol production using cassava flour fc
Flow chart for Cassava Starch fc
Flow Chart for Production of High Quality Cassava Chips
Garri production fc