The physical properties of pistachio nut and its kernel as a function of moisture content and variety. Part III: Frictional properties Original Research Article

In this study, the frictional properties (emptying and filling angles of repose and static coefficient of friction on five structural surfaces) of five Iranian commercial varieties of pistachio nut and its kernel (namely; Akbari, Badami, Kalle-Ghuchi, Momtaz and O’hadi) were evaluated as a function of moisture content (at five levels ranged from fresh pistachio nut at harvesting to commercially dried conditions). The results showed that the emptying angle of repose of nuts was the greatest for Kalle-Ghuchi (27.36 ± 0.59) and the least for Badami (25.09 ± 1.74) at all moisture contents studied. However, in kernels, the greatest value was offered by O’hadi (28.48 ± 1.61) and the lowest by Akbari (26.924 ± 0.97). The filling angle of repose of pistachio nuts and kernels was the highest for Badami and the lowest for O’hadi at different moisture levels. Both angles of repose of pistachio nuts and kernels decreased linearly as the moisture content decreased. The static coefficient of friction value for Badami nut variety on all five structural surfaces (fiberglass, glass, galvanized iron sheet, plywood, and rubber) was the greatest, but in case of kernel, the greatest value was observed for Kalle-Ghuchi (0.503–0.615) on rubber surface and the lowest for O’hadi (0.333–0.512) on fiberglass surface. The highest friction coefficient for all pistachio varieties (both nut and kernel) obtained on rubber surface and the lowest on fiberglass surface at all moisture content levels. The static coefficient of friction of both nuts and kernels on all five test surfaces decreased linearly with decreasing the moisture content.