Comparative analysis of moisture-dependent physical and mechanical properties of two varieties of African star apple (Chrysophyllum albidum) seeds relevant in engineering design

Abstract

• Physical and mechanical properties of two varieties [big (udara) and small (nwannu)] of African star apple between 3.00% to 18.03% w.b were determined. • Geometric, gravimetric and frictional properties of the two varieties of African star apple increased with moisture, except angle of repose (frictional property). • Galvanized sheet surface showed the maximum coefficient of static. • Angle of repose was maximum for the udara variety • Mechanical properties decreased with increase in moisture content for the transverse, vertical and horizontal loading orientation. This study was conducted to investigate and compare the engineering properties of two varieties [big (Udara) and small (Nwannu)] of African star apple ( Chrysophyllum albidum ) seeds in Nigeria. The objectives were to determine the effect of moisture on some moisture-dependent physical and mechanical properties of the Udara and Nwannu seeds. The parameters considered were geometric (axial dimensions, mean diameters, surface area, sphericity, aspect ratio, and volume), gravimetric (bulk and true densities, 1,000 seed mass and porosity), frictional (angle of repose and static coefficient of friction) and mechanical (rupture force, rupture energy and deformation at rupture point) properties of the seeds in the moisture content range of 3.00–18.03% (w.b.). It was observed that moisture content have a significant effect on all the engineering properties studied at p ≤ 0.05. The result also revealed that the angle of repose of Udara seed was higher than Nwannu seed. The coefficient of static friction of the star apple seeds was greatest on the galvanized sheet surface, 0.526 for Nwannu seed and lowest on the aluminum surface, 0.210 for udara seed. The coefficient of static friction was higher on all surfaces for Nwannu seed than for Udara seed. The force required to rupture the seed, the rupture energy, and the deformation at rupture point of Udara and Nwannu seeds decreased with increase in moisture content for horizontal (x), transversal (y) and vertical (z) loading direction. The transverse position showed the highest values of rupture force for both, Udara and Nwannu seed, but higher in Udara than Nwannu variety. The lowest rupture force was obtained during horizontal loading for the two varieties but lower in Nwannu than Udara seed. Similar results were obtained for rupture energy. The vertical loading position indicated the highest deformation at rupture point for both, Udara and Nwannu seed, but higher in Udara than Nwannu, while, the lowest deformation at rupture point was recorded in transverse loading for the two varieties, but lower in Nwannu than Udara seed. Properties of kernels, grains, and seeds are essential in the development of equipment for transportation, handling, and processing.