Moisture-Dependent Engineering Characterization of Psyllium Seeds: Physical, Frictional, Aerodynamic, Mechanical, and Thermal Properties

Purpose: The analysis of the engineering properties of food and agricultural products is necessary to design processing, sorting, handling, sizing, and other postharvesting equipment. Methods: The engineering properties of psyllium seeds (PSs) as a function of moisture content (MC, 4.32–20.38% d.b.) were assessed. The regression linear and polynomial models with high coefficients of determination were also fitted to the data to explain the significant effect of moisture content on different engineering properties. Results: An increase in axial dimensions with increasing MC led to a significant increase in volume (1.27–1.45 mm3), surface area (4.51–4.98 mm2), and sphericity (51.7–52.5%) of PSs. However, the bulk (654.16–601.35 kg/m3) and true (1265.1–1074.7 kg/m3) densities and porosity (48.29–44.04%) were reduced by increasing MC. Increasing the MC led to a significant increase in repose angle (32.30–39.61°) and terminal velocity (1.51–2.41 m/s). The galvanized iron sheet (0.423–0.519) had the highest static friction coefficients compared to glass (0.261–0.332), stainless steel (0.369–0.426), and plywood (0.393–0.458) surfaces. The rupture force was significantly decreased by increasing MC. Under the vertical loading orientation, PSs required less compressive force to rupture compared to the horizontal loading orientation. The specific heat (1.56–3.12 kJ/kg K°) and thermal conductivity (0.235–0.322 W/m K°) were increased by increasing MC, while the thermal diffusivity (2.3–1.7 × 10−4 m2/s) decreased. Conclusions: Since MC had a key role in changing engineering properties of PSs, the resulted regression equations can be applied for extracting mucilaginous polysaccharides from PSs grown in other geographical areas with different weather conditions. © 2021, The Korean Society for Agricultural Machinery.