Strength properties of the Bambara kernel (Vigna subterranean) as influenced by the moisture content and kernel size

The fracture resistance of food grains is an essential piece of information required for the optimum design and development of agricultural post-harvest machinery. In this study, the strength properties of two varieties of Bambara kernels (TVSU-1395 and TVSU-1353) were examined in terms of the mean rupture force, absorbed energy, and deformation as affected by the moisture content and kernel size. To achieve this, a quasi-compressive force was applied on the two varieties of Bambara kernels of varying moisture contents (5.43%, 7.24%, 9.01%, 11.54%, and 13.62% wb) and kernel sizes (small, medium, and large) in between the loading compartments of a universal Testometric device at a 20 mm/min loading rate. The experiments take ten treatments with 20 replications subjected factorially to a completely randomised design (CRD) into consideration. The results revealed that the force needed to initiate the kernel fracture increased with an increase in the kernel size and moisture content from 101.44 to 235.06 N and 74.69 to 190.49 N for TVSU-1395 and TVSU-1353, respectively; whereas the energy at the kernel fracture point increased in a range of 0.074 to 0.401 J and 0.062 to 0.141 J for TVSU-1395 and TVSU-1353, respectively. The kernel deformation increased with the moisture content and size from 0.654 to 3.746 mm. These infer that the large kernel size of the TVSU-1395 variety at a 5.4% moisture content had greater compressive strength than the TVSU-1353 variety. The kernel moisture and size exhibited a strong correlation (0.958 ≤ R2 ≤ 0.997) with the strength parameters. The results of this study will help the food industry in designing energy-efficient post-harvest equipment for Bambara kernel processing. Further studies may consider the strength attributes of Bambara kernels at varying rates of loading, kernel orientations, and varieties to optimise the best process conditions for the post-harvest handling of different Bambara cultivars and develop labour-saving decorticating machines.