Mechanical Behaviour of Unshelled Moringa oleifera Seeds at Varying Moisture Contents

Abstract

The determination of mechanical properties of unshelled Moringa oleifera seeds was studied under compression test at varying orientations and moisture contents for postharvest equipment design. A completely randomized block design (CRBD) was applied in designing the experiment. The impact of varying moisture content levels of (10.25, 17.33, 24.47, and 32.34% dry basis) on the applied force at bio-yield and rupture, deformation, energy at rupture, crushing strength, and elastic modulus of the seed samples were investigated. Polynomial functions of the 2nd order with coefficients of correlation ranging between 0.642 ≤ R2 ≤ 0.999 gave the best fit and described the resulting relationships between the studied properties with respect to moisture levels at the two loading axes. Results obtained showed that the seed samples had maximum values of 80.3 N, 110 N and 257.2 J, for bio-yield force, rupture and rupture energy respectively at (10.25% d.b., in the horizontal orientation; whereas minimum values of 31.5 N, 54.9 N and 51.3 J for bio-yield force, rupture force and rupture energy occurred at (32.34% d.b.) respectively in the vertical orientation. Also, the maximum compressive strength of 5.8 N mm-2 in the horizontal orientation of the seed samples at 10.25% d.b. whereas the minimum compressive strength (2.5 N mm-2) occurred in the vertical orientation at 10.25% d.b. moisture content. The sample exhibited less resistive strength to crushing in the horizontal position as the moisture increased; whereas in the vertical position, the cell’s vertical edges provide some form of shield against external pressure which resulted in increased crushing resistance per contact area of the sample.