Engineering characterization of Persian walnut and its kernel (Juglans regia L.) for obtaining high quality produce

Abstract

Knowledge of walnut fruits properties as a function of moisture content is crucial for the efficient processing of the product and optimizing oil extraction. Several engineering properties such as average geometric diameter, unit mass, surface area, volume and sphericity were evaluated in Persian walnut and its kernel. All the parameters increased as the moisture content increased from 3.41 to 17.65% dry basis. For the bulk density, true density, porosity and repose angle of nuts, the moisture dependent changing ranges were 315.51-300.12 kg/m3, 688.05- 664.83 kg/m3, 54.11-54.85%, 38.05-39.1°, respectively, while the corresponding values for kernels were 377-364 kg/m3, 1,043.6-1,028.7 kg/m3, 63.87%-64.61%, and 40.6-41.5°, respectively. The static coefficients of friction range on glass, steel, galvanized iron sheet and plywood were 0.284-0.293, 0.276-0.301, 0.307-0.321 and 0.404-0.426 for nuts and 0.322-0.332, 0.312-0.323, 0.348-0.360 and 0.443-0.451 for kernels, respectively. The force required for initiating nut rupture at a loading rate of 50 mm/min decreased from 534.2 to 406.7 N, 69.6 to 26.92 N and 195.2 to 133.3 N, by increasing moisture content for x-, y-, and z-axis orientations, respectively. With an increase in the moisture content, the absorbed energy for fracture of walnut and its kernel increased. Kernel fracture was more resistant in the z-axis orientation of loading for all moisture content levels.