The Impacts of Different Oven-Drying Temperatures on the Elemental Profile and Microstructural Integrity of black bean(Akidi) Seeds

This study examined how oven-drying temperature affects the mineral content and physical structure of black beans (Akidi), a protein-rich legume vital to sub-Saharan African diets. Fresh cowpea seeds were dried at 45, 50, 55, 60, and 65°C in a forced-air oven. Freeze-dried seeds served as the control. Mineral analysis was conducted using energy-dispersive X-ray spectroscopy, and structural changes were observed with scanning electron microscopy. Results showed significant temperature effects. Carbon and oxygen levels decreased with rising temperatures, dropping from 63.5% to 49.8% and 26.4% to 20.4% respectively, due to moisture loss and organic compound volatilization. Conversely, mineral concentrations increased substantially — potassium rose from 3.2% in fresh seeds to 10.5% at 65°C. Sulphur followed a non-linear pattern, indicating thermal degradation at higher temperatures. Structural examination revealed progressive seed coat deterioration. Minor wrinkling appeared at 45°C, micro-cracks formed at 50°C, crack networks developed at 55–60°C, and complete structural collapse with mineral aggregation occurred at 65°C. The findings indicate that moderate drying temperatures between 50–55°C offer the optimal balance. This range achieves meaningful mineral concentration while maintaining seed coat integrity essential for storage and processing. These results provide scientific guidance for improving post-harvest handling of cowpeas, supporting better nutritional security through optimized preservation protocols.