Fracture resistance of sunflower seed and kernel to compressive loading

Abstract

The fracture resistance of both a sunflower seed ( Helianthus annuus L.) and its kernel was measured in terms of average compressive force, deformation and energy absorbed per unit volume at rupture. Samples at various moisture contents were loaded in vertical and horizontal orientations. The force required for seed hull or kernel rupture decreased as moisture content increased from 4% to 20% d.b. Seeds loaded in the horizontal orientation developed hull cracks at a lower level of force than those loaded in the vertical orientation. For the kernel, the trend was the opposite. The average compressive forces required to cause kernel rupture were substantially lower (13.4–8.5 N) than those required to rupture the seed (65.2–35.3 N) in both orientations. The maximum deformations of the seed at rupture were 1.34 and 1.46 mm under horizontal and vertical loading orientations, respectively, while for the kernel these values were 1.73 and 2.32 mm. Energy absorbed per unit volume at rupture increased with an increase in moisture content. The seeds loaded in a vertical orientation absorbed more energy (144.7–222.9 J/m 3) prior to rupture than those loaded in the horizontal (95.2–184.2 J/m 3) orientation. Kernels loaded in a vertical orientation required less energy (18.1–54.3 J/m 3) to rupture than those loaded in the horizontal (38.9–65.8 J/m 3) orientation.