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

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 simultaneously by the same
plant. The yam species is highly neglected in the region such that it is only consumed in the rural
areas 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. This
study revealed the high nutritional values of D. bublifera in terms of proximate and mineral
composition, and its safety in terms of anti-nutrient contents, coupled with numerous literature reports
on its medicinal potentials. We therefore advocate for increased cultivation, utilization and valorisation
of the species in the area and beyond to enhance food and nutrition security.