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Constraints and projections for processing and utilization of Cassava


Mechanized processes of cassava detoxification
Utilization of detoxified cassava in poultry feeds
Projections
Constraints
References

S. O. Onabowale

The possibility of substituting cassava for maize in the diet of laying and growing chickens was investigated. The hydrogen cyanide contained in cassava was detoxified using three different methods namely: fermentation, acid hydrolysis, and a combination of both. Acid hydrolysis was most effective in removing 98% of the total cyanide content of the cassava tuberous roots while fermentation, combined with acid hydrolysis and fermentation alone, reduced cyanide content by 95% and 87.84% respectively. Detoxified cassava diet was then formulated and used in feeding tests on chickens. Egg production efficiency of chickens fed on the cassava-based formulation was higher (71.43%) than egg production (66.67%) from chickens fed on maize-based ones. In growing chickens, the detoxified cassava rations produced no adverse effect on performance and mortality. An added advantage was that the cassava-based feed was cheaper than the maize-based feed.

Cassava (Manihot esculenta Crantz), also known as manioc or yuca in some parts of the world, has been a major food crop in Nigeria for more than a century. Cassava is considered an important source of energy in Nigerian diets. Cassava is known to produce 250000 calories/hectare/day compared to 200 000 for maize, 176 600 for rice, 114 000 for sorghum and 110 000 for wheat.

Poultry production is an important industry in Nigeria which has more poultry than all other African countries (FAO 1980). Consumption of poultry meat is also increasing faster than that of other kinds of meat in Nigeria. Feed represents a major proportion of the overall production cost in the poultry and livestock industry in Nigeria (Longe and Adetola 1983). A major constraint in the industry is the availability of feed ingredients all the year round at economic prices. This problem is further compounded by the fact that most of these ingredients are imported, at high foreign exchange costs. For example, the amount of maize imported in 1982 cost Nigeria the foreign exchange equivalent of over 14 million. Therefore, alternative sources of energy for animal feeds which are nutritionally adequate and cheap must - be found locally to reduce the cost. One source of great potential which is increasingly being used for animal feeds is cassava which can completely replace maize in livestock and poultry feed- formulation.

Raw cassava roots must be used immediately, processed, or preserved, in order to prevent decomposition. Moreover, the presence of toxic hydrogen cyanide in cassava is a limiting. factor in its use as food for man and livestock. Thus, processing helps to remove or reduce the level of toxic cyanogenic glucosides present in the cassava root, as well as altering the availability energy of the cassava. Many traditional methods have been developed in various parts of the world for preparing cassava for human consumption and feed. These vary according to the form in which the cassava is to be consumed from simple sun-drying to complex methods involving fermentation (Wyllie et al. 1984). Modern methods of detoxification of cassava for poultry feeds which is highly mechanized has been developed at FIIRO (Federal Institute for Industrial Research, Oshodi, Nigeria) in addition to the traditional processes. These modern methods are used to detoxify cassava, which can then be used to compound poultry feeds.

Mechanized processes of cassava detoxification

Detoxification of cassava whole tubers (unpeeled), cassava waste, and cassava peel for the removal of residual cyanide can be achieved by fermentation, acid hydrolysis, and fermentation followed by acid hydrolysis.

Fermentation process

Washing and grating: The first stage of this process consists of washing the unpeeled cassava tubers which have been previously cut into small sizes, or the cassava waste or cassava peel. The washed cassava samples are then fed through a conveyor to a grater where they are properly grated to specific size.

Fermentation: The grated cassava or the cassava mash is poured into a 400-litre tank which had been constructed from plastic, fiber glass, or such other materials as aluminium. A known quantity of water is added to the cassava mash, mixed thoroughly and left to stand for 24 hours. Because of the toxic hydrogen cyanide given off, it is essential that adequate ventilation is provided.

Dehydration or dewatering: The fermented liquid cassava mash is dewatered, using either a basket centrifuge and hydraulic press or a screw press to produce a thick fermented cassava cake of about 45-47% moisture content.

Drying: The fermented cassava cake is normally broken down into small pieces and fed directly into a fried rotary louvre dryer at temperatures of about 75°- 100°C where the moisture content is further reduced to a low level in order to give dried cassava cake a long shelf life.

Sieving: The dry cassava cake is sieved using a sieving machine with a mesh aperture of 450m m-2mm, 630m m-2mm and 1000m m-2mm for unpeeled cassava tubers, cassava waste, and cassava peel respectively.

Milling and packaging: The oversized particles of cassava cake or grit are milled to the particle size of the sieve, using the Bentall disc attrition milling machine. The final powdery detoxified cassava products are then collected and packaged in cellophane bags ready for use for ration formulation at rates varying from 40-45 % of the concentrate mixture for poultry.

Hydrogen cyanide determination: The hydrogen cyanide levels of the cassava mash before fermentation, after 24 hours fermentation, and of the final detoxified cassava products are determined using the modified method of the AOAC ( 1972) (table 1).

Acid hydrolysis process

In this process, the washing and grating stage adopted in the fermentation process is also used. In acid treatment process, a known concentration of mineral acid, such as concentrated hydrochloric acid previously diluted with water to give a known strength of the acid, is added to the cassava mash, mixed thoroughly and allowed to stand for 2 hours for acid hydrolysis to take place. This is followed by the neutralization of the acid with a known concentration of mineral alkali such as sodium hydroxide for 5 minutes. Dewatering, drying, sieving, milling, packaging, and hydrogen cyanide determination as in the process of fermentation, are also carried out.

Fermentation coupled with acid hydrolysis process

The cassava is fermented as described in the fermentation- process, after which it is subjected to the acid hydrolysis process. Dewatering, drying, sieving, milling, packaging, and hydrogen cyanide determination are also carried out. The detoxification processes of cassava (whole tuber, waste, or peel) for the removal of toxic residual cyanide are shown in figure 1.

Figure 1: Flow chart for mechanized detoxification processes of cassava for feeds

Table 1. pH and hydrogen cyanide contents during detoxification of cassava

Cassava material

Untreated

After 24 hrs

Final product

% loss HCN

After 24 hrs

After acid hydrolisis

Final product

% loss HCN

Untreated

After acid hydrolisis

Final product

% loss HCN

Unpeeled tuber


HCN (ppm)

156.00

83.20

18.98

87.84

83.30

15.60

7.80

95.00

156

6.50

3.00

98.00


pH

6.03

5.25

nd

nd

4.17

4.10

nd

nd

6.03

4.04

nd

nd

Cassava peel


HCN (ppm)

180.00

52.50

18.46

89.75

52.58

14.30

9.10

95.00

180

7.00

4.00

97.73


pH

5.37

3.91

nd

nd

3.78

4.08

nd

nd

5.37

4.30

nd

nd

Cassava waste


HCN (ppm)

130.00

75.00

20.80

84.00

76.50

12.20

10.40

92.00

143

7.80

4.68

96.73


pH

5.54

3.75

nd

nd

3.80

4.20

nd

nd

5.83

4.70

nd

nd

Note: nd = not determined

The dewatered cassava cake is granulated with a hammer mill to an appropriate particle size that will facilitate heat transfer during drying. The wet detoxified cassava granules are fed into a drier of the tray, the fluidized-bed, or the rotary type and dried to a low moisture content to make it shelf-stable. The close relationship composition between cassava and maize makes it possible to substitute cassava for maize in the production of livestock and poultry feeds as an energy and carbohydrate source. An example is the cassava peel (table 2). The leaves of cassava, especially in the dried forms, can be incorporated into the ration for pigs, poultry and dairy cattle.

Table 2. Proximate composition of maize and dried cassava peel (% dry matter)

Ingredient

Dry matter

Crude protein

Crude fiber

Ether extract

Ash

Nitrogen- free extract

Maize

86.2

8.8

2.5

3.6

1.4

83.6

Cassava peel

87.6

5.1

15.7

2.1

6.1

71.0

The mechanized process of fermentation is essentially similar to the traditional method, but machinery and equipment have been employed to replace manual labor for unit operations. Also, additional steps have been added to the traditional method in order to confer on the detoxified cassava, and thus the feed, a long shelf-life, good consumer appeal, and improved wholesome conditions.

Utilization of detoxified cassava in poultry feeds

The detoxified cassava products (whole tuber, waste, or peel) have been supplemented with other locally available ingredients and vitamins at FIIRO to provide a complete feed formulation for growing and laying chickens at rates varying from 40 to 50 % of the concentrate mixture. Findings from animal feeding studies show that the detoxified cassava-based feeds compared well with the control (a maize-based commercial product). Egg production efficiency of chickens fed on the cassava-based feed was higher (71.43%) than that (66.67%) in chickens fed on maize-based diet (table 3). In growing chickens, the detoxified cassava-based rations produced no adverse effect on bird performance and mortality; percentage survival was high in all cases.

The cassava-based grower feed also enhanced growth rate which was manifested by the rapid gain in weight of the chickens. The feed conversion efficiency of the cassava-based feed was the same as that of the maize-based commercial feed. The cassava-based feed did not have any adverse effect on the vital organs.

Projections

Investment requirements for a cassava feedmill and the profitability of setting up such a mill depend largely on the cheapness of available cassava. It is also necessary to project the cost of the equipment/machinery, utilities, and chemicals necessary for the detoxification processes of cassava.

Table 3. Effects d cassava-based diets on chickens

Parameter

Group

Control

Experiment I

Experiment II

Initial body weight (g)

500- 1045

585-950

660-870

Average weight gain/week(g)

117.50

209.00

111.28

Survival rate (%)

85

100

88

Average feed intake week(g)

704.78

760.46

689.81

Average water intake/week(ml)

1697.59

1743.94

1458.38

Total no. of eggs produced

96

105

99

Weight of whole egg produced (g)

40.5-60.5

38.4-63.9

40.0-57.8

Egg size (cm)

5.60-8.95

5.35-9.50

6.00

Egg production efficiency (%)

66.67

71.43

61.91

Feed concentrate efficiency (kg/dozen eggs)

2.08

1.99

2.10

Notes: The chickens used for control were on a diet of Mitchell growers and layers feed; chickens for experiment I were on a diet of cassava-based layers and growers feed; and chickens for experiment II were on a diet of cassava-based layers feed.

The following lists the required machinery and equipment, utilities and chemicals, along with some of their 1988 costs in Nigeria.

Machinery and equipment

· Cassava grater (4 tonnes/hr)
· Pulper/mixer
· Aluminium tank (400-litre)
· Hydraulic press
· Hammer mill
· Blower
· Packaging equipment
· Weighing scale

Utility requirements

· Clean water

1500 litres/hr

· Electric power

60 kw, 3 phase

· Diesel oil

153 litres

· Polythene bags

12 pieces- 0.53/piece

Current prices of utilities

Water

18.00

Diesel oil (30 kobo/litre)

45.90

Electricity for 8 hrs

33.00

Polythene bags

6.36

Subtotal

03.86

Current prices of equipment and chemicals

Cassava grater

990.00

Dryer

12500.00

Mixer

12500.00

Hydraulic press

12500.00

Hammer mill

12500.00

Blower

12500.00

Aluminium tank

1000.00

Concentrated HCl (2.5-litre)

40/bottle

Caustic soda pellets

40/50 kg

Insurance

1580.00

Subtotal

16 220.00

From these prices, at least 16,324 will be required for equipment purchase and installation, chemicals, and utilities. For a cassava plantation, about 1000 acres of land will be necessary. The price per acre varies according to the location and this will directly affect the price of cassava roots per ton.

Constraints

The bulk of cassava grown in Nigeria is produced by peasant smallholders under traditional agricultural practices. Consequently, the average yield is low, ranging from 710 tonnes per hectare, which is much lower than the world average of 30-40 tonnes per hectare.

Moreover, the cost of cassava has been unstable during the last five years. Increased labor wages for planting and harvesting and increased cost of transporting harvested tubers to processing plants as well as erratic climatic patterns seem to have affected the price of cassava.

Another constraint of utilizing cassava for feed is the competition for cassava by man for food and industry. Cassava is utilized in the production of gari, fufu, cassava flour for human consumption, and for industrial starch used in textile industry. Thus, the amount of cassava available for the production of animal feed is very much reduced.

References

AOAC (Association of Official Analytical Chemists) . 1972. Official methods of analysis. Washington, DC, USA.

FAO (Food and Agriculture Organization). 1980. Production year book 34: 211.

Longe, O. G., and J.A. Adetola. 1983. Metabolizable energy values of some agricultural wastes and industrial by-products for layers and effects of these ingredients on gut dimensions. Journal of Animal Production Research 1 (3): 1.

Wyllie, D., M. Mtui, J. D. Oloya, and J. A. Kategile. 1984. The processing of cassava meal for chicks. Nutrition Reports International 30 (5): 1127- 1136.


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