Studies on Nutrient Potentials of Blends of Treated Aerial Yam (Dioscorea Bulbifera) and Cowpea (Vignaunguiculata L. Walp) Fed Adult Albino Rats

Abstract

This work evaluated the nutrient and antinutrient content and nutritive value of a lesser-known high yielding crop (aerial yam) and well-known high yielding legume cowpea. Aerial yam and cowpea used in this work were obtained from a family farm in Ovoko, Igbo-Eze South Local Government Area, Enugu state, Nigeria. Four kilogrammes of both foods were harvested. Aerial yam was cleaned, washed, allowed to dry, and divided into three equal portions. Cowpea was also cleaned, washed, allowed to dry and divided into three equal portions. The first portion of aerial yam was peeled, cut into small round sizes, spread out in a wide wooden basket and sun-dried, milled, packaged in cellophane bags, name labelled and stored in a cool place until used. The other two portions were soaked in tap water in a ratio of 1:3 (w/v), drained, spread on a wet jute bag, covered well with another wet jute bag, allowed to germinate, and divided into two portions after germination. The first portion was treated as the first ungerminated sample. The third portion was soaked in a container in tap water in a ratio of 1:3 (w/v) and left for fermentation by inherent microflora enzymes. After fermentation, the samples were dried, milled and packaged as others. Cowpea first portion was spread in a wooden mesh, sun dried, milled and packaged and stored safely until used. The other portion was germinated as aerial yam and treated the same. The last portion was treated as aerial yam and stored for analysis. Various nutrients and antinutrients were estimated using standard techniques. The flours were used to formulate rat diets containing 1.6g N or 10% protein (nitrogen basis). Twenty adult albino rats (100-200)g were allotted to 4 diets based on these two foods (aerial yam and cowpea). Other nutrients, eg. Oil, mineral and vitamins were added to produce four adequate diets for the rats. Both germination and fermentation increased nutrient contents of the two foods and equally reduced their antinutrients. The protein and mineral bioavailablity of these flours was high as judged by the result of nitrogen balance and liver composition of adult rats based on composites of the flours. Both germination and fermentation increased moisture from 7.68 to 8.63% in aerial yam and 7.78 to 8.24% in cowpea. These processes either single or combination of the two increased protein from 17.76 vs 19.26% in cowpea. Combination of the two processes caused increase in fibre only, in aerial yam (3.18 vs 3.97%) when compared with the control. Both processes decreased carbohydrates in aerial yam (65.37 to 62.21 and 60.10%) and cowpea (67.85 to 63.85 and 62.80%) in both flours. Both treatments increased zinc, iron, calcium and phosphorous. Phytate and tannins decreased due to the processes, except for that of germinated cowpea (4.87 vs 4.79 and 4.32% for aerial yam and 4.61 vs 3.97% for cowpea). Haemaglutinin and oxalate were decreased by the treatment. On the other hand, they increased saponins (0.048 vs 0.07 and 0.11% in aerial yam, 0.01 vs 0.09 and 0.12% in cowpea). Nitrogen solubility, fat absorption capacity, water absorption capacity and foam absorption capacity increased as against their controls (35.48 vs 37.78 and 39.15%, 34.22 vs 36.60 and 38.26mg) for aerial yam and cowpea respectively. Both germination and fermentation increased mineral and protein bioavailability of the diet and liver composition of adult rats fed these diets.