Determination of some engineering properties of morama bean (Tylosema esculentum)

Abstract

The morama bean (Tylosema esculentum) is an underutilised legume native to the Kalahari region of Southern Africa. Some engineering properties relevant to the mechanisation of its processing have been characterised, namely; size, shape, surface area, projected area, volume, density, porosity, 1000-grain mass, static angle of repose, static coefficient of friction and texture. At moisture content of 7.4% (w.b.), the average length, width and thickness of the beans were 19.25, 17.21 and 13.39 mm, respectively. Geometric mean, equivalent diameter and arithmetic mean diameters were 16.4, 16.51 and 16.61 mm, respectively. Morama beans are spherical in shape, having average sphericity of 85.45%, aspect ratio of 0.90 and flakiness ratio of 0.78. Surface area, projected area and volume of the beans were 850.43 mm2, 261.95 mm2 and 2,352.82 mm3, respectively. Mean true and bulk densities were, respectively, 1075.13 and 795.31 kg/m3 with bulk porosity derived as 25.76%. Mean 1000-grain mass was 2.21 kg. Static angle of repose was 12.98o, while static coefficient of friction of morama against plywood, galvanized iron, stainless steel, plastic, and itself, were 0.2, 0.26, 0.2, 0.18, and 0.24, respectively. Texture analysis by flat-plate compression testing showed that the beans required an average of 546.78 N to break and absorbed up to 470.03 mJ of energy before breaking, with hardness computed as 120.52 N/mm.