Comparison of Mechanical Properties of Some Selected Almond Cultivars With Hard and Soft Shell Under Compression Loading

Abstract

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). PRACTICAL APPLICATIONS 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.

The Effects of Moisture Content, Compression Speeds, and Axes on Mechanical Properties of Walnut Cultivars

“…The decrease in rupture force may be a result from softening the walnut at higher moisture content. Similar conclusions were also made by Braga et al (1999) for macadamia nut; Güner et al (2003) for hazelnut; Khazaei et al (2002) and Aktas et al (2007) for almond; and Sharifian and Derafshi (2008) for walnut.…”

“…where P r is the rupture power required of walnut (W), E is the rupture energy (mJ), V is compression speed (mm/min), and D is the corresponding deformation at the rupture point (Olaniyan and Oje 2002;Khazaei et al 2002;Aktas et al 2007). …”

“…In recent years, several researchers have investigated the mechanical properties of various nut crops affected by moisture content for macadamia nuts (Braga et al 1999), shea nuts (Olaniyan and Oje 2002), groundnuts (Olajide and Igbeka 2003), hazelnuts (Güner et al 2003), pine nuts (Özgüven and Vursavuş 2005), almond nuts (Aktas et al 2007), olives (Kılıçkan and Güner 2008), and peanuts (Akcali et al 2006) by testing them against various compression axes. Dursun (1997), Koyuncu et al (2004a, b), Sharifian and Derafshi (2008), and Altuntas and Ozkan (2008) investigated the mechanical behavior of walnuts under compression loading.…”

Characterization of texture attributes of raw almond using a trained sensory panel

“…400 N to achieve the shell's rupture. On the other hand, the European cultivars showed a resistance of the shell greater than 600 N, and in the case of 'Supernova' almost 1,000 N. The comparison of 'Nonpareil' with a hard-shelled Turkish cultivar showed rheological differences between them, and it was concluded that the industrial processing should be different per each cultivar [23].…”

Mechanical behaviour and split resistance of chestnut under compressive loading

“…So far many studies have been conducted on physical and mechanical properties of hard shelled nuts and kernels as hazelnut, pistachio nut, apricot, pine nut, almond, walnut, macadamia nut and cashew nut by Oloso & Clarke (1993), Liu et al (1999), Borghei et al (2000), Aydın (2002), Gezer & Dikilitaş (2002), Aydın (2003), Güner et al (2003), Vursavuş & Özgüven (2004), Vursavuş & Özgüven (2005), Aktaş et al (2007), Arslan & Vursavuş (2008) and Galedar (2009). There are also a few studies on physico-mechanical properties of chestnut.…”