Some physical properties of Roselle (Hibiscus sabdariffa L.) seeds as a function of moisture content

Three cultivars of Roselle seeds (“Mexico”, “China”, and “Sudan”) were collected from Guerrero State, Mexico and reconditioned to moisture contents ranging from ca. 13% to 25% w.b. The reconditioned seeds were then evaluated for dimensions, sphericity, bulk density, true density, porosity, thousand seed mass, and static coefficient of friction on several material surfaces. In the range of analyzed moistures, physical properties of Roselle seed are related to the moisture content by quadratic equations. Cultivars Mexico, China and Sudan increased their width in 10.9%, 7.8%, and 8.1%, in that order; similarly, their length was increased in 13.1%, 9.8%, and 7.2%, and their thickness was increased in 8.3%, 4.0%, and 13.7%. Seeds from the cultivar Mexico were the smallest. The sphericity changes with the increase in moisture content. Each cultivar had a single behaviour, thus cultivar Sudan comes closer to a spherical form, contrary to the cultivars Mexico or China. The bulk density and the true density for different moisture levels decrease with the increase in moisture content. The estimated porosity was found to increase with the increase in moisture content. The porosity started at 52.9%, 53.3%, and 54.7% and increased to 57.7%, 55.1%, and 56.9% for cultivars Mexico, China, and Sudan, respectively. The thousand seed mass increased with increase in seed moisture content from 21.85 to 81.00 g, 35.22 to 40.62 g and 36.37 to 41.78 g for the three cultivars mentioned above, respectively. The cultivars evaluated showed a comparable behaviour in relation with the static coefficient of friction, this variable increased with moisture content on four structural surfaces, namely concrete (0.32–0.34), galvanised iron (0.27–0.30), glass (0.25–0.30) and wood (0.23–0.30).