Physical properties of bambara groundnuts from Botswana

Physical properties of bambara (Vigna subterranea (L.) verdc.) seeds landraces from Botswana with mean moisture content (dry basis) 7.17–8.99% were evaluated in this study. The landraces were Zimbabwe Red (National Tested Seed Red – NTSR), Botswana Red (BotR), Diphiri cream (DipC1 & DipC2) and speckled (AS17). The mean value for length, width and thickness of bambara seeds ranged from 11.01 to 11.81 mm; 9.41 to 9.96 mm and thickness 9.05 to 9.48 mm, respectively. The size of the bambara seeds was graded as large (>10.5 mm), medium (9.50–10.49 mm) and small (<9.50 mm). Geometric mean diameter, volume and surface area of bambara seeds ranged from 9.59 to 9.98 mm and 435 to 498 mm3, 2608 to 2987 mm2, respectively. The NTSR, BotR and DipC1 were significantly (p < 0.05) higher in geometric mean diameters, volume and surface area when compared with the others. The values of sphericity, aspect ratio, 1000-seed weight, bulk density and true density of bambara seeds ranged from 84.2% to 88.3%, 82.1% to 88.1%, 0.5037 to 0.5971 kg, 757.8 to 780.1 kg/cm3 and 1000.2 to 1004.7 kg/m3, respectively. NTSR are longer while DipC2 are shorter in length than the others. DipC1 is wider and thicker while AS17 is less broad and thicker than others. The AS17 is significantly (p < 0.05) heavier than the others followed by the DipC1 and DipC2. DipC2 is more spherical and occupies more volume and area when compared to the other landraces. The porosity and angle of repose of bambara seeds ranged from 22.20% to 24.24% and 17.1° to 19.8°, respectively. The seeds of bambara are irregular in shape and size, are spherical and will roll rather than slide. Knowledge of these physical properties will make the design of hoppers, storage facilities, separation and cleaning process, cooling, heating and other similar processes for bambara seeds a possibility.