Moisture dependent physical and mechanical properties of Syrjan region wild pistachio nut

Abstract

The wild pistachio (Pistacia Atlantica Mutika) exists in 2.4 million hectares of Iranian forest. In this way the pistachio of Syrjan was chosen as the case of study. The objective of this study was to determine physical and mechanical properties of wild pistachio nut of Syrjan rejoin as a function of moisture content. The physical properties including thousand unit  mass, length, width, height, arithmetic mean diameter, geometric mean diameter, surface area, true density, bulk density, porosity, repose angle (emptying and filling) and coefficient of friction were determined at  four different levels of moisture content. The nut was compressed along the length and thickness at 0.045, 0.069, 0.089 and 0.188 (d.b.) moisture contents to determine required force, deformation and energy per volume (toughness) at rupture point. The nut average length, width, thickness were 7.31, 6.17 and 4.90 mm, respectively at moisture content of 5.5 (%, w.b.). The greatest true density was 1081 kg/cm³. With increase moisture from 4.84 to 13.65 (%, w.b.) the bulk density of nut decreased from 658.21 to 636.68 kg/m³, porosity decreased from 37.52 to 32.86%, the emptying angle of repose increased from 32.04 to 34.6 degree, and the filling angle of repose increased from 29.95 to 31.59 degree. The greatest friction coefficient of the nut was obtained on galvanized iron surface and the minimum value on aluminum surface at all moisture content levels. At all levels of moisture content the rupture force, deformation at rupture point and toughness of the nut were the minimum values along the nut thickness (Z-axis). The minimum values of the rupture force, deformation and toughness were 175.16 N; 1.03 mm; and 0.49 mJ/mm³, respectively.

Keywords: Wild pistachio, nut, moisture content, Syrjan, physical properties, mechanical properties