Characterization of Morphology and Structural and Thermal Properties of Legume Flours: Cowpea (Vigna unguiculata L. Walp) and Bambara Groundnut (Vigna subterranea L. Verdc.) Varieties

Bambara groundnut and cowpea legume seeds with a very high nutritive value are widely produced and consumed in most sub-Saharan African countries. The aim of this work which is part of a large study was to compare the potential of bambara groundnut and cowpea varieties of flour as basic raw material for the preparation of a widely legume-based food product known as koki. Toward this objective standard methods were used to analyze some morphological, microstructural and thermal properties of these legume flours along with their respective isolated starches and proteins. In general, thermal transition of proteins has slow enthalpy energy of less than 1 J g(-1). The gelatinization temperature and the enthalpy of gelatinization of starches in the flours were lower as compared to those of isolated starches, suggesting here an interaction of starch with other components during the gelatinization process. All starches are of A-type and the degree of crystallinity of bambara starch was higher than that of cowpea starch. Scanning electronic microscopy revealed that starch granules of North cowpea (NC), West cowpea (WC) and White bambara groundnut (WB) were polygonal while that of Black bambara (BB) starch were spherical in shape. The flowability characteristic of the flour and starch shows that bambara flour with small particle size (similar to 90% < 100 mu m) had a high compressibility (47.38-43.16%) as compared to cowpea flour (32.18-30.24%). NC and VB starch granules have a size between 10 and 35 mu m while WC and BB are too small (6-15 mu m). NC and WB starch granule sizes are between 10 and 35 mu m while WC and BB's sizes are too small (6-15 mu m). Bambara groundnut and cowpea flour along with their respective isolated starches and proteins therefore appears to be a valuable raw material which may be useful for the preparation of many food products.