The effect of moisture contents on the physical properties of both bambara groundnut seeds and pods in South Africa

Abstract

Bambara groundnut (Vigna subterranean (L) Verdc) is an indigenous African crop. In South Africa, the crop is grown by rural subsistence farmers. This crop is classified as a drought-tolerant crop and it can produce good yields in poor soil conditions. However, statistics show that Bambara groundnut production is currently neglected by industries due to the lack of research on the crop focused on postharvest technologies, and agro-processing. Current research on the crop is mostly focused on agronomic and growing characteristics. Data on the physical properties and processing equipment for the Bambara groundnuts are limited. The objectives of this study were to investigate the effect of moisture contents on both Bambara groundnut seeds (shelled) and pods (unshelled). The physical properties of the pods and seeds were measured at three moisture content levels. The finding showed that axial dimensions, geometric mean diameter, sphericity, volume, and weight increase as moisture content increases. The static coefficient of friction of seeds and pods increased from 0.15 to 0.19 and 0.29 to 0.31, respectively. Simirlarly, the bulk density of shelled and unshelled groundnuts increased from 500 to 955, and 355 to 422 kg.m-3, respectively. The results also showed that the true density of seeds rose from 994 to 1832 kg.m-3 and for the unshelled groundnuts it increased linearly from 532 to 655 kg.m-3. The required forces for cracking both bambara groundnut seeds and kernels showed a declining trend as moisture increased from 6 to 20%. The cracking forces required for Bambara groundnuts kernels at 6, 15, and 20 % are 32.5 ±12 N, 29.9 ±15.3 N, and 28.9 ±9 N, respectively. As the moisture increased, the data deviation from the mean decreased from 16.30 to 10.1 N. In terms of designing agro processing eqiupment or machinary such as a shelling machine, the physical properties from the lower moisture content are recommended. Key words: cracking force, physical properties, moisture content, Bambara groundnuts