Comparative Nutritional and Phytochemical Evaluation of the Aerial and Underground Tubers of Air Potato (Dioscorea bulbifera) Available in Abakaliki, Ebonyi State, Nigeria

Abstract

The wild yam species (Dioscorea bulbifera), known as edu in Abakaliki, Ebonyi State, Nigeria, has two types of edible tubers (underground tubers and aerial bulbils) produced by the same plant. The yam species is highly neglected in the region and all over the world such that it is only consumed in the rural areas of the region often not out of preference but at periods of food scarcity. Both tuber forms are consumed in Abakaliki. The objective of this study was to evaluate and compare the nutritional and antinutritional profiles of the two tuber forms. The proximate and phytochemical constituents were determined using standard official methods of the Association of Analytical Chemists while mineral elements were quantified by Atomic Absorption Spectrophotometry (AAS) method. The study revealed no significant difference between the tuber forms in their contents of crude fats, fibre ash and carbohydrates and calorific values (P>0.05) while crude protein was significantly higher in the aerial bulbils (P<0.05). The mineral elements K, Na, Ca, Mg, Fe, Zn, Cu and P but Mn were all significantly higher in the underground tubers while the heavy metals Cd, Pb, Cr, Ni, Se and Co were not detected. Oxalate, tannins and phenols were significantly higher in the underground tubers while the bulbils were richer in alkaloids, HCN saponins and flavonoids. Compared with nutritional values of common edible yam species in the literature, this study also showed that this neglected yam species is a good source of protein, lipid, crude fibre, carbohydrates and minerals. Its contents of the toxic substances (phytate, oxalate, tannins, alkaloids and HCN) were not exceedingly higher compared to common yams. Considering the levels of proximate, minerals and phytochemicals and also the various literature reports on the medicinal potentials of D. bublifera, we advocate for increased utilization of this yam species in the area and beyond to reduce food crisis.