DETERMINATION OF THE CYANIDE CONTENT IN SOME BITTER CASSAVA SPECIES IN PARTS OF OHIMINI L.G.A OF BENUE STATE
CHAPTER ONE
INTRODUCTION
1.1    Background to the Study

Cassava (Manihot esculenta crantz) is a perennial crop native to tropical America [1, 2]. It originated from Brazil and was introduced to Africa by Portuguese traders in the 16° century [3]. Cassava is a tuberous, woody, shruby plant of the Euphorbiaceae (spurge family), characterized by palmately lobed leaves, inconspicuous flowers, and a large starchy tuberous root with a tough, papery brown bark and white to yellow flesh [4]. This plant and root is also known as yuca (in Spanish), manioc, mandioca and tapioca (when dried to a powdery or pearly extract) [4].
Cassava is a starchy staple whose roots are very rich in carbohydrates, a major source of energy. It is the third largest source of food carbohydrates in the tropics, after rice and maize [5, 6]. Cassava is a major staple food in the developing world, providing a basic diet for over half a billion people [7]. However, cassava is a poor source of protein and reliance of cassava as a staple food is associated with the disease kwashiorkor [4]. Cassava is the source of flour called tapioca, as well as is used for bread and alcoholic beverages [4]. It is one of the most drought-resistant crops, capable of growing on marginal soils.

The roots and leaves contain cyanogenic glycosides which offer protection against some herbivores, but also makes the plant toxic to humans if consumed without prior treatment such as leaching and drying [4]. The mature cassava root has three distinct tissues: bark (periderm), peel (cortex) and parenchyma. The parenchyma, which is the edible portion of the fresh root, comprises approximately 85 % of the total weight, consisting of xylem vessels radially distributed in a matrix of starch containing cells [8]. The cyanogenic glycosides concentration in cassava varies in different parts of the plant, according to variety, location, age, and environmental conditions. They are a number of varieties, sweet cassavaterm bitter cassava    opposed to sweet cassava, refers to the taste of theroot parenchyma. Bitterness is associated with higher levels of cyanogenic glycosides [9]. Cenain ecological stress factors such as, pest attacks, prolonged drought and low phosphorous and potassium levels in the soil may cause roots to acquire bitterness, and this coincides with an increase in the level of cyanogenic glycoside [10]. Bitter cassava varieties are more drought resistant and thus readily available and cheaper [11]. A study on the assessment of growth and yield of some high and low-cyanide cassava genotype in acid utisols of Southeastern Nigeria records outstanding performance for fresh storage root yield in some high-cyanide (bitter) cassava genotypes and hence recommended for farmers in the  

In Africa, cassava is extensively produced providing significant energy to the population. It is the staple food of more than 500million people in the tropics whom are very poor [9] but present literature shows that they is increasing demand for cassava production in Asia and other parts of the world. The crop offers the advantage of a flexible harvesting time, allowing the farmers to keep the root in the ground until when needed [13]. In addition, the crop produces well under limiting growth conditions. In Africa, it is recognized as a famine reserved crop due to its tolerance to drought and infertile soils, and its ability to recover from disease and pest attacks. Nigeria is the world�s largest producer of cassava. Thailand is the largest exporter of dried cassava [4].
1.2    Statement of the Problem
Cassava is widely grown in Nigeria with Benue State being one of its major regions where the crop is heavily cultivated and used for making fermented products such as fufu (local name, �    �) and garri. Its utilization as food varies from region to region. It is a source of food security, not only because it can be grown on less productive land, but because it is a source of income for the urban and rural populations. People in many parts of Nigeria rely largely on starchy foods for their carbohydrate intake and cassava being the major source of
carbohydrate    is becoming a major source of    food. The    �s  agronomic

advantages such as high productivity ease and flexibility of cultivation, tolerance
 
to drought and its ability to grow well on relatively poor soils has made it rapidly and extensively adaptable. The status of cassava as a food security crop to most subsistence farmers is however threatened by pests, diseases and the potential toxicity in cassava.
As earlier stated, the presence of cyanogenic glycosides in the cassava is a potential for production of poisonous hydrogen cyanide. The cyanogenic glycoside in cassava is called linamarin. The hydrolysis of linamarin produces hydrogen cyanide and acetone and this occurs when the plant tissue is damaged by pest or predator attacks, environmental factors such as prolonged drought and even human activities such as harvesting. Studies on cyanide concentration in cassava have been done in various parts of Benue State but none have been carried out in Ohimini Local Government Area. The present work will consider the variation in cyanide content in the parenchyma of the bitter cassava root at different locations in Ohimini Local Government Area of    Benue State using the UV-visible spectrophotometric method of determination.
1.3    Aim of Study
To determine quantitatively the amount of cyanide contained in different cultivars (TMS 30572, TMS 98/0581, TMS 30211, and TMS 98/0068) of the parenchyma of bitter cassava variety collected from selected locations in Ohimini L.G.A. of Benue State.
 
1.4    Objectives of Study
The objectives of this study are;
i.    To determine the cyanide concentration of fresh tuber parenchyma of bitter cassava cultivars grown in the selected districts of Ohimini L.G.A of Benue State.
ii.    To establish the effectiveness of boiling and drying (i.e. oven and air drying) as methods used to detoxify the high cyanide content in bitter cassava.
1.5    Significance of Study
The information obtained from this study on quantitation of cyanide in bitter cassava will be crucial for awareness campaigns to its consumers and the general public. Furthermore, such information will be important for extension services geared towards educating farmers and consumers by agricultural officers and other regulatory bodies on the effective methods for processing bitter cassava.
1.6    Scope of the Study
The study only covers three (3) districts in Ohimini L.G.A. of Benue State and concerns with the quantitation of cyanide in the bitter cassava variety from the three districts (Oglewu, Okpiko and Unyangede) in the Local Government Area.