Physical and Engineering Properties of Nine Cowpea Varieties and Local Maize from Malawi–Mozambique for Dehulling Design

It is widely recognized that grain variability affects the physical and engineering properties of cowpea and maize varieties. Understanding the effects is vital for designing a dehulling machine that can yield better performance. The physical and engineering properties of nine cowpea varieties and a local maize variety were determined to provide essential data for the design of dehulling and processing equipment. Standard laboratory methods reported in the literature were used to analyze the grains. The study reveals that the physical and engineering properties of nine cowpea and maize varieties varied considerably (p < 0.05). The mean values of moisture content % ranged from 10.06 to 13.81%, length ranged from 7.11 to 11.44 mm, width ranged from 5.65 to 10.28 mm, thickness ranged from 4.60 to 6.73 mm, and thousand-grain weight ranged from 100 to 364 g. Da ranged from 5.79 to 8.89 mm, Dg ranged from 5.66 to 8.59 mm, sphericity ranged from 0.73 to 0.86, surface area ranged from 101.38 to 233.75 mm2, and volume ranged from 97.05 to 339.82 mm3. Furthermore, the COF on stainless steel ranged from 0.30 to 0.37, the angle of repose ranged from 20.03 to 30.33°, the bulk density ranged from 688.00 to 814.67 kg/m3, the true density ranged from 1079.91 to 1282.61 kg/m3, and the porosity % ranged from 60.53 to 67.46%. Lastly, grain hardness ranged from 56.27 to 267.91 N, grain compressive energy ranged from 80.91 to 664 mJ, grain stiffness ranged from 6.48 to 26.13 N/mm, seed coat–cotyledon/pericarp–endosperm stickiness force ranged from 0.04 to 0.10 N, Adhesiveness (force to overcome stickiness) ranged from 0.08 to 93.42 N · mm, and fracturability ranged from 56.27 to 267.91 N. These results offer a comprehensive engineering database for the design and optimization of dehulling and post-harvest processing equipment.