Influence of moisture content on physical and mechanical properties of almond (Prunus dulcis cv. Fra Giulio Grande).

摘要

Various physical and mechanical properties of almonds (cv. Fra Giulio Grande) and kernels were determined at 4 moisture contents (9.74, 16.35, 23.28, 30.46% wet basis (w.b.)). The average length, width, thickness, equivalent diam., unit mass, vol. 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 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% w.b. In the moisture range 9.74-30.46% w.b., studies on rewetted nuts 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. Nut true density decreased from 826 to 730 kg m-3, while for kernel it decreased from 922 to 844 kg m-3. Nut porosity increased from 40.94 to 45.08%, while kernel porosity 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 coeff. of friction for nuts on 3 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. Corresponding values for kernels were 0.335-0.441, 0.381-0.496 and 0.484-0.589, respectively. The max. force for nut cracking occurred in the longitudinal direction and the min. force transversely in the thickness direction. For all compression directions the force required to crack the nut decreased with increasing moisture content. Results may be useful for developing and optimizing equipment for handling and cracking almond cultivars.