ABSTRACT
Bitter yam (Dioscorea dumentorumpax) can also be called trifoliate yam which belongs to the genus Dioscorea and family Dioscoreacea. It is an annual plant with an underground storage tuber in which starch is deposited. This work was aimed at assessing the nutritional and phytochemical compositions of Dioscorea dumentorum commonly cultivated in south eastern Nigeria.Dioscorea dumentorum was washed and shade dried for 6 days. The dried yam was ground using a milling machine and then stored in a plastic container for further analysis. Qualitative and quantitative analysis was carried out to test for tannin, saponins, alkaloid etc. The result obtained in phytochemicals are alkaloid (++), phenol (++) and flavonoids (++)were present, steroids and tannin were absent while saponins was relatively low (+).and phytochemical results showed that the quantity of alkaloid, flavonoid and phenol were 0.5%, 11.6% and 1.89% respectively. The results for proximate analysis shows that moisture content is 61.6%, ash content 8%, crude fiber 10.45% etc. In conclusion, the present study has shown that Dioscorea dumentorumcontains appreciable activities commonly consumed tubers. The study further revealed that it contains phytochemicals such as flavonoids, alkaloids and saponins which could be extracted for human use and may be responsible for its anti-diabetic and other pharmacological activities. And it is clear from this study that, these tuber owe their anti-diabetic and analgesic properties to their selective chemical composition, and that proper knowledge of the proximate and phytochemical composition is fundamental to understanding their presence and nutritive capabilities.
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).
This protein content is comparable to those of cereals, and higher than 4%value for dehydrated cassava tuberous roots (UNECA 1985).
Manuel et al.,2005 reported yam to be one of the principal foods in Nigeria, also an economically, socially and traditionally valuable crop in many tropical countries predominantly in West African, south Asian and Caribbean Countries.
Yam has been reported to be rich in carbohydrate with many of its varieties widespread throughout the humid tropics. The most economically important species grown are; white yam (Dioscorea rotundata), yellow yam (Dioscoreacayenensis), water yam (Dioscoreaalata), chinese yam (Dioscoreaesculenta), Aerial yam (Dioscoreabulbifera) and trifoliate yam (Dioscoreadumentorum) (Ike and Inom, 2006) but only a few species are cultivated as food crops to some extent processing of food has not reached a significant level commercially.
Predominantly, the use of yam has been limited to the preparation of local dishes such as pounded yam (yam dough)and porridges (Amaniet al., 2002). The production of instant yam flour, yam flakes and starch has been explored but industrial scale production has been limited due to various constraints including high fresh market price (Onayemi and Potter1974;FAO 2005). In other words, some yam varieties are widely known and overexploited for food while others are known and exploited as food only in a few rural communities in Nigeria and as a result underutilized. Over dependence on the common yam varieties for food and industrial use account for the high market price of yam and this incidentally limits industrial exploitation.
Bitter yam is a speciesof yam in which limited work has been done in terms of its production and utilization though it is high yielding compared to other yam species. In Nigeria, its local names include;Esuru in Yoruba language, Ona in Igbo language and kosanrogo in Hausalanguage. Some of its other common names are three leaved yam, cluster yam. It has starch grains that are smaller, more soluble and more digestible than those of other yam species (Treche and Guion 1980). The proteins also are more balanced than those of white yam (Mbome and Treche 1994) and it is rich in vitamins and minerals. The consumption of bitter yam is restricted due to its bitter taste, inability to keep for longer time after harvesting and poor binding capacityofits flour (Martin et al., 1993; Mbome and Treche 1994; Sefadedeh and Afoakwa2001).
1.1. PHYTOCHEMICAL ANALYSIS
Phytochemicals are chemical compound that occur naturally in plant (phyto means ‘plant’in Greek. They are responsible for color and organoleptic properties, such as the deep purple of blueberries and smell of garlic. Phytochemical analysis is determination of metabolic nutritional values and medicinal values in food and plant product.
There are two methods of test in phytochemical analysis; quantitative and qualitative test
1.2 PROXIMATE ANALYSIS
Proximate analysis refers to the determination of the major constituents of food and it is used to assess if a feed is within its normal compositional parameters or somehow been
There are 6 methods of test in proximate analysis; ash content,crude protein, crude fiber, moisture content and carbohydrate
1.3 STATEMENT OF THE PROBLEM.
To study how beneficial are Dioscorea dumentorum in producing phytochemicals their quantitative and to have a basic knowledge of their respective proximate composition as regards consumption. To compare the phytonutrients present in these leaves. To gather a background knowledge of their concentrations and to assess their potential nutritive and medicinal benefits
1.4 AIMS
This work was aimed at assessing the nutritional and phytochemical composition of Dioscorea dumentorum commonly cultivated in south eastern Nigeria (Enugu)
1.5 OBJECTIVES
I. To determine the qualitative phytochemicals presents in Dioscorea dumentorum (bitter yam).
II. To determine the quantitative phytochemicals present in Dioscorea dumentorum (bitter yam).
To determine the proximate composition of Dioscorea dumentorum (bitter yam).================================================================
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