Physical properties of cowpea grains during drying

The objective of this work was to evaluate the influence of moisture content on the physical properties of cowpeas (Vigna unguiculata) during drying. Samples of manually harvested and threshed cowpeas with an initial moisture content of 0.250 (b.s) were dried in a forced air oven at 40 °C until the final moisture content was 0.13 ± 1 (b.s). Drying was followed by determining the mass difference, with the initial moisture content being known. The following physical properties during drying were determined for the predetermined moisture content: the angle of repose, bulk density, real density, intergranular porosity, mass of thousand grainsand shape factors [sphericity, circularity (for the natural repose position), geometric diameter and the surface-volume ratio]. The main characteristic dimensions of the grains (largest, intermediate and smallest) were measured during drying in order to determine the shape factors. There was an increase in the bulk and realdensities and in the sphericity, circularity and surface-volume ratio factors during drying. The other physical properties (mass of a thousand grains, angle of repose and intergranular porosity), as well as the geometric diameter had a reduction in their values as the water content decreased during drying.