Comparison of mechanical properties of some selected almond cultivars with hard and soft shell under compression loading

The mechanical properties of Nonpareil versus Gulcan 101-23 almond cultivars that have different shell properties were loaded between two parallel plates to determine the rupture force, rupture energy, rupture power requirement, toughness and firmness. The tests were carried out with three moisture contents, namely, 7.2, 22.9 and 33.6% wet basis and three loading axes (x, y, z). Physical characteristics of the almond cultivars such as length, width, thickness, geometric mean diameter, sphericity, volume, surface area and weight were determined. Physical properties of both cultivars increased as a numerical by increasing moisture content. The highest rupture force in all moisture content levels was obtained for almond pit loaded along the y-axis. In addition to rupture force, values of absorbed energy, toughness, power requirement and firmness were calculated as mechanical properties. The maximum force required to initiate pit rupture was found as maximum 554.3 N at y-axis for 7.2% moisture content and minimum 126.9 N at x-axis for 33.6% moisture content for Gulcan 101-23 cultivar. These values were determined as 53.3 and 11.2 N, respectively, for Nonpareil cultivar. Rupture force, absorbed energy, toughness, power requirement and firmness decreased with an increase of moisture content. The difference between mechanical properties of Nonpareil versus Gulcan 101-23 almond cultivars was found to be highly significant (P < 0.001). As almond production increases in the world, almond processes are performed by hand or by using old techniques. Therefore, major quality loss during harvesting and postharvesting processes of almonds occurs. The most critical and delicate operation in postharvesting processes is pit cracking to extract the fragile whole edible kernel from the almond pit. This process is still carried out by hand or by using an apricot cracking equipment. But this is not the right process because shell hardness of almond pit changes in relation to almond cultivars. While some almond pits can be cracked using high power and some apparatus, some of them can be cracked even by hand easily. The cracking operation causes damage and broken kernels because of the excessive mechanical forces. The extent and type of damage depend on the physical characteristics, cultivar and applied force. For this reason, systems must be designed while taking these criteria into consideration to prevent inadequate applications. © 2007, The Author(s); Journal compilation © 2007, Blackwell Publishing.