CHAPTER ONE

1.0 INTRODUCTION
1.1 Background Of The Study
Yam (dioscorea spp.) is a multi-species crop that originated principally from Africa and Asia before spreading to other parts of the world (Hahn et al.,1987). It belongs to the family of dioscoreae within the genus dioscorea and serves as a staple crop in west Africa.(Asiedu et al., 1992). There are many cultivars of yam, though only six are important as staple foods in the tropics. the economically important species grown are Dioscorea rotundata(white yam),D.alata (yellow yam),D.bulbifera (aerial yam), D.esculenta (Chinese yam) and D.dumenterum (trifoliate yam). Yam tubers which is the most important part of the plants can be stored longer than other root and tuber crops. This ensures food security even in times of general scarcity. Yam is the third most important tropical root and tuber crop after cassava and sweet potato (fu et al., 2005). West Africa is the leading producer of yam and grows over 90% of the worldwide production (40 tonnes fresh tuber/year) followed by the west Indians where Jamaica is the leading producer (FAOSTAT,2004). Nigeria is the world’s largest producer of yams followed by Ghana, ivorycoast and togo (FAO,2003). Both fresh tubers and yam flour are now exported from Ghana and Nigeria to developed countries such as united kingdom and united states of America. These are mostly patronized by emigrants from growing regions according to the Nigerian export promotion council (NEPC) Nigeria realized N56 billion in 2007. Sustainable production and utilization of yam are important steps in enhancing food security and alleviatind
2
poverty particularly in west Africa where it is estimated to provide more than 200 dietary calories each day for over 60 million people (Nweke et al.,1991., FAO 2002).
Yam is consumed in different forms,mainly boiled,fried or baked.tubers are often dried and milled into flour for various product,boiled yams,poundes yams and amala are the forms of yam mostly consumed in west Africa especially Nigeria and benin (Akissoe et al.,2001). Yam production faces many constraints among which are production cost (mainly planting material and labour cost),post-harvset losses(low yields). Water yam (Dioscorea alata) posses a higher multiplication ratio and tuber yields as well as better storability than the preferred indigenous species such as D.rotundata, D.alata is popular and prevalent abakaliki agro ecological zone of ebonyi state Nigeria where it is called ‘Mbala or Noula’ (igbo names) (Udensi et al.,2008) even though D.alata is also eaten boiled,it is less preferred to D.rotundata varieties. D.alata can also be processed into flour and reconstituted into fufu though generally D.alata contains less sugar and has an extended shelf-life (Raemackers,2001) which ensures availability in times of scarcity.it is also known for its high nutritional content,with crude protein content of 7.4%,starch content of 75-84% and vitamin C content of ranging from 13.0-24.7mg/100g (Osagie.1992).breeders are therefore kein to improve the food quality of the species as it has good agronomic characteristics.
3
1.2 STATEMENT OF THE PROBLEMS
The principal problem in yam production that has been identified is the high cost of seed yam, high labour requirement, diseases, pest as well as high post harvest losses(Orkwor 1998).another constraint to yam production is the limited processing technology. About 30% of harvested yam tubers are lost to waste. The bulkiness of fresh transport and low margins for both farmers and traders are thus a matter of serious concern in the urban market (Cooke et al.,1988).
During the processing of yam through sun-drying method,the problem encountered is the loss due to potential contamination of the product variability in drying time, rain damage and so on. Ohweever, D.alata fresh texture is usually not firm as the D.rotundata (white yam) and less suitable than other species for the preparation of the most popular food product from yam in the west Africa region(Wireko-manu et al.,2011).
Finally, during the production of flour from yam, in the western part of Nigeria (the yorubas), the yam flour produced which is called “AMALA” is normally brownish in colour and dark in nature, hence does not have a good quality and colour. Technologies therefore have been discovered to bring about the production of yam flour that has a high quality and a good colour and texture.
4
1.3 OBJECTIVE OF THE STUDY
1.3.0 MOTIVATION
The growing need for the variety of food in Nigeria has become a primary concern for the urban and rural households in Nigeria. In recent times, the concern has raised much researcher’s interest to do related studies. As reported in many different studies around the world, food security is a common problem.
1.3.1 OBJECTIVES
The present study aims at carryout an experiment on fresh yams, optimize the drying parameters and investigate the effect of drying conditions on the quality of the yam. To result to this, the present study which will address particular issues food drying could stimulate producers, farmers, agriculturists, educational practitioners on the phenomenon of drying to enhance the quality of yams to solve past harvest losses.