Fracture resistance of pine nut to compressive loading

A pine nut was loaded between two parallel plates to determine the rupture force, deformation, power and firmness required to initiate nut rupture. The tests were carried out at five moisture contents of 5.33, 11.87, 18.30, 23.53 and 30.09% d.b., and two orientations (vertical and horizontal). The pine nut was positioned vertically, with the major axis of the nut parallel to the direction of loading. For horizontal loading, the major axis of the nut was normal to the direction of loading, or lengthwise. Physical characteristics of the nut and kernel such as mass, dimensions, geometric mean diameter, sphericity, volume surface area and shell thickness were determined. The force required to initiate nut rupture decreased from 713.61 to 219.26 N and from 520.14 to 248.86 N for the vertical and horizontal orientations of loading with an increase in moisture content. Deformation at rupture point and the power required for cracking the nut decreased in magnitude with an increase in moisture content for loading in the vertical and horizontal orientations. Firmness values decreased with an increase in moisture content in the horizontal orientation but this decrease continued until moisture content of 23.53% d.b. in the vertical orientation of loading. Especially, at all of the moistures, there was always the tendency of kernel breakage for loading along the horizontal orientation. The results provide useful data for use by engineers in the design of a suitable pine nut cracking machine. (c) 2004 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.