Mechanical properties of the parenchyma of potato (Solanum tuberosum cv. Russet Burbank)

Abstract

The mechanical properties of plant materials and plant structures influence the form, function, distribution, and utilization of plants. The shear and compressive stiffnesses of different regions of potato parenchyma were measured to more fully characterize the mechanical properties of this important storage organ. Measurements were performed on tubers that had been stored for 1 and 10 months. Slices and cylinders of parenchyma were excised from the centre of the tubers in three directions (and slices from the outer portion in two directions). Slices were subjected to small-strain oscillatory shear at frequencies of 0.02, 0.2, and 2 Hz. Cylinders were subjected to three cycles of uniaxial compression at 2 and 20 cm∙min−1. The coefficient of variation of measured parameters ranged on average from 16 to 44% for both crops and both tests. At small strains, potato parenchyma behaved essentially as an elastic material. The results from both small-strain oscillatory shear and uniaxial compression suggested that potato parenchyma is anisotropic in nature. Slices from the outer and inner regions of the tuber had different shear stiffness values. The shear stiffness of tubers stored for 1 month was approximately 70% greater than those stored for 10 months. Repeated compressive loading of potato parenchyma cylinders ameliorated the differences in stiffness and energy absorption between short- and long-term stored tubers, attributable to movement of fluids from the cells during compression. The observations emphasize the complexity of potato tissue and how its mechanical properties change during storage. Keywords: shear, compression, energy absorption, stiffness, turgor, storage, anisotropicity.