Comparative analysis of new Persian walnut cultivars: nut/kernel geometrical, gravimetrical, frictional and mechanical attributes and kernel chemical composition

Abstract

This study compared some chemical and engineering attributes of three Persian walnut cultivars (Toyserkan, Chaboksar and Karaj) at a moisture content of 3.41% (d.b.). The study experimentally investigated engineering properties of the nut and kernel of walnuts, such as dimensions, the geometric mean diameter, surface area, sphericity, bulk and true densities, porosity, dynamic angle of repose, and static coefficient of friction on four structural surfaces namely, glass, galvanized iron sheet, plywood and steel, as well as nut and kernel rupture force and rupture energy. Chemical analysis showed that carbohydrate content was significantly higher in the Karaj cultivar than in the other two studied, and that the Chaboksar cultivar had the highest fat content. The Toyserkan cultivar had the highest values for protein and minerals (Ca, P, K, Mg, Fe, and Cu). Moreover, most physical properties of nut and kernel were significantly different for each cultivar. The values for sphericity, true density and repose angle for nuts were 83.8–94.0%, 315.5–402.3kgm−3 and 35.3°–38.0°, respectively, while the corresponding values for kernels were 63.7–72.4%, 1018.9–1043.3kgm−3 and 39.8–41.0°, respectively. The ranges of static coefficients of friction on plywood, galvanized iron sheet, glass and steel were 0.385–0.473, 0.307–0.433, 0.284–0.432, and 0.268–0.293 for nuts and 0.348–0.453, 0.332–0.436, 0.306–0.336 and 0.322–0.369 for kernels, respectively. Also, kernel rupture force and energy and the required energy for nut rupturing were significantly different for each cultivar. The Toyserkan cultivar under the Y-axis loading direction had the lowest the force and energy for initial kernel and nut rupture.