Technical Note: Influence of Moisture Content on Physical and Mechanical Properties of Almond (Prunus dulcis cv. Fra Giulio Grande)

Abstract

Various physical and mechanical properties of almond (Prunus dulcis cv. 'Fra Giulio Grande') nuts and kernels were determined at four moisture content levels (9.74%, 16.35%, 23.28%, and 30.46% wet basis). The average length, width, thickness, equivalent diameter, unit mass, volume, and sphericity of nuts were 36.77 mm, 26.70 mm, 19.01 mm, 26.51 mm, 6.06 g, 9.83 cm3, and 72.13%, respectively, while the corresponding values for kernels were 25.98 mm, 16.19 mm, 8.63 mm, 15.33 mm, 1.57 g, 1.93 cm3, and 59.01%, respectively, at a moisture content of 9.74% wet basis (w.b.). In the moisture range from 9.74% to 30.46% w.b., studies on the rewetted nut showed that the bulk density of nut and kernel decreased from 488 to 401 kg m-3 and from 559 to 475 kg m-3, respectively. The true density of nut decreased from 826 to 730 kg m-3, while for kernel it decreased from 922 to 844 kg m-3. The porosity of nut increased from 40.94% to 45.08%, while porosity of kernel increased from 39.43% to 43.69%. The projected area for nut and kernel increased from 745 to 823 mm2 and from 318 to 357 mm2, respectively. In the same moisture range, the static coefficient of friction for nuts on three different material surfaces varied from 0.291 to 0.415 on aluminum, from 0.338 to 0.462 on plywood, and from 0.392 to 0.529 on rubber. The corresponding values for kernels were 0.335 to 0.441, 0.381 to 0.496, and 0.484 to 0.589, respectively. The maximum force for nut cracking occurred in the longitudinal direction and the minimum force transversely in thickness direction. For all compression directions, the force required to crack the nut decreased with increasing moisture content. The results of this study could be applied to optimize and develop of machines for handling and cracking of this almond cultivar.