3-D Microscale Geometry of Apple Tissue using X-Ray Computed Microtomography

The microstructure and the connectivity of the pore space are important variables for better understanding of the complex transport phenomena that occur in apple tissue. In this study, we present geometrical properties (i.e., porosity and specific surface area) and spatial distributions for nodal pore volume, nodal pore size, tortuosity, coordination number, and pore path length obtained from a representative elementary volume (REV) of 1.3 mm3 of apple tissue. For comparison, two different regions of the sample were analyzed: in the fleshy part of the apple (‘cortex tissue’, ~6mm from the peel) and near to the core line (‘core tissue’, ~10mm from the core center). The apple tissue was imaged using X-Ray computed microtomography with a pixel size of 8.5 μm. The spatial distributions were computed based upon three dimensional medial axis analysis of the void space in the image and using the average of six apples (variety ‘Jonagold’). Results showed that microtomography provides micrometer resolution to quantitatively analyze and characterize apple tissue. The minimum REV of apple tissue was estimated to be 1.3 mm3. Comparisons among the parameters extracted from the two analyzed regions showed significant differences (p<0.05). The porosity and specific surface area for cortex tissue and core tissue were 31±3% and 1.8x10±1.2x10μm and 17±4% and 1.4x10 ±2.7x10μm, respectively. The complexity and variability of the pore space network tissue taken from two different regions of the apple, highlighted the difficult of creating a unique network for 3-D representation of apple tissue, and therefore, the physically-realistic pore network characterization of apple tissue cannot be adequately represented using simple average parameters of the total tissue.