CHAPTER ONE 1.0 Introduction Bitter yam (Dioscoreadumentorumpax) can also be called Trifoliate yam which belongs to the genus Dioscorea and family Dioscoreaceae (Onweme 1978;Bai and Ekanayake, (1998).it is an annual plant with an underground storage tuber in which starch is deposited (Bai, and Ekanayakeet al.,1998). The starchy tubers may be single but are usually produced in clusters, in a stand of the plant(Bai, and Ekanayake). Though the plant still exists in the wild of tropical Africa,its cultivated landraces are considered amongst food yam of economic importance(Hahn, S.K,Osiru, D.S.O,Akoroda, M.O and Otoo, J.A(1987). The flesh of the tuber may be white or pale-yellow or dark yellow, with the cultivated variety eaten as food after boiling to softness (Coursey,Kay et al., 1967) while yam tubers are known to be rich in vitamin c (Coursey Kay etal1967 and Degras, 1993). Tubers of Dioscorea species generally contain phytochemicals (Degras,1993). Some of these phytochemicals are toxic at high concentrations while others are relatively beneficial or harmless the major non nutritional compounds found in yams include alkaloids, saponins, phenols and oxalates (Degras,1993). Dioscorea dumentorum is sometimes of the land races referred to bitter yam because of the bitterness of the tubers of the wild type and few cultivated landraces. This bitterness is known to be caused by the presence of a toxic alkaloid;dihydrodioscrine 6.dihydrodioscorine is structurally similar, but less potent than the bitter and toxic dioscorine found in the Asiatic dioscoreahispida(Degras, 1993).
Trifoliate yam (bitter yam)has benefited from great selection pressure by African civilizations to such an extent that cultivars of the plantin Africa have little or negligible quantity of the bitter alkaloid. Nutritionally, bitter yam is superior to other food yams in Africa in terms of protein content. The protein content of the tuber on dry matter basis is 12-13% (Onweme1978, Coursey, D et al 1967; Oyenuga, 1968, Bell et al., 1981).