PROXIMATE (NUTRIENT CONTENT) ANALYSIS OF DIOSCOREA BULBIFERA

ABSTRACT

This study is part of the effort to find out and document the nutrient compositions of the Dioscorea bulbifera (Aerial yam on air potato). Dioscorea bulbifera is among the many species of yam that can be found on Nigeria. The tissue is known to be a good source of food nutrients such as carbohydrate, crude protein, crude fat, fibre, Ash and moisture. As in many other yam species, moisture (64%) constitutes the greatest composition in percentage, followed by carbohydrate (29.03%), crude protein (1.1%), Ash (1.5%), crude fibre (0.67%) and crude fat (0.4%), with crude fat being the lowest in quantity. Dioscorea bulbifera is also known to contain some mineral elements such as potassium, calcium, phosphorous, magnesium, iron, zinc, copper, and sodium. Among the mineral elements potassium is found to be the highest while magnesium the lowest.

CHAPTER ONE

1.1 Introduction and literature Review

Dioscorea bulbifera (Aerial yam or Air potato) belongs to the family of dioscoreaceae. It is a vigorous climber plant reaching up to 6 meters or more with smooth stems ranging from 1 to or more with smooth stems ranging from 1 to 8mm in diameter, twinning in clockwise direction. It is found in both Africa and Asia, with slight differences between those found in the two places (Hamon et al., 1995). The leaves are cordate-orbicular to ovate-orbicular, strongly acuminate, 15-30cm long and broad; the petioles are thickened at the base with ear-like projection that often encircled the stem. The flowers are small (though larger than those of many cultivated yams), about 3mm long, closely appressed to the pedicel in long axillary or terminal racemes. The leaves and bulbils of Dioscorea bulbifera are used for traditional medicine in many areas (Coursey, 1997). The yam specie produces aerial starchy bulbils which are usually grey or brown in colour with white or yellow mucilaginous flesh; they are about the size of potato (hence the name air potato) ranging from about 3 to 10cm in diameter and usually weight about 0.5kg but can be as heavy as 2kg. Dioscorea bulbifera is cultivated for their bulbils which are consumed once they are cooked like potatoes in water with oil and other local ingredients or by boiling. Apart from starch, the bulbils contain other chemical elements such as protein, fats, fibres and minerals (Tindall, 1983; Abara et al., 2000). Dioscorea bulbifera is cultivated at the beginning of the raining season form March to June. Bulbils are formed at the leaves armpit. In African races of the plant, these bulbils are sharply angled, while those of Asian races are spherical to ellipsoid. The ground tubers arise from a swelling of the young stem and enlarged rapidly as storage organs. Both bulbils and tubers are edible although tubers are usually hard, bitter and unpalatable, and selection for the bulbils appears to have taken place in early times as some varieties, both Asian and African lack significant underground tubers. Bulbils are usually harvested after senescence and death of the plant. At that period of vegetable cycle of the plant, the bulbils fall down. For farmers, the fall of the bulbils is the only one indication of maturity in the Dioscorea bulbifera.

Dioscorea bulbifera is one of the group of crops termed roots and tubers which together with cereals such as maize, rice and wheat constitute the main source of energy in the tropics, widely grown and consumed amongst various communities in the tropics.

The edible species of Dioscorea bulbifera are grown and distributed extensively in West Africa. The Caribbean Islands, South, East Asia and West India. The wild forms occur mainly in Africa and Asia. Dioscorea bulbifera is a good source of calories and minerals such as Iron, calcium and phosphorous (Tindall, 1983; Abara et al., 2000). The moisture, ash, protein, fat, fibre and carbohydrate content of yam vary among species and between cultivars.

Data from available literature indicates that yams are generally low in fat and protein, but high in moisture and carbohydrate content. (Ferguson et al, 1980).
Aims and Objectives

This study was undertaken to determine the nutrient contents of Dioscorea bulbifera (Aerial yam or Air potato).

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