ORIGINAL ARTICLE Three-dimensional pore space quantification of apple tissue using X-ray computed microtomography Fernando Mendoza Æ Pieter Verboven Æ Hibru K. Mebatsion Æ Greet Kerckhofs Æ Martine Wevers Æ Bart Nicolaı ¨ Received: 19 October 2006 / Accepted: 16 February 2007 / Published online: 15 March 2007 Ó Springer-Verlag 2007 Abstract The microstructure and the connectivity of the pore space are important variables for better understanding of the complex gas transport phenomena that occur in plant tissues. In this study, we present an experimental procedure for image acquisition and image processing to quantita- tively characterize in 3D the pore space of apple tissues (Malus domestica Borkh.) for two cultivars (Jonagold and Braeburn) taken from the fleshy part of the cortex using X- ray computer microtomography. Preliminary sensitivity analyses were performed to determine the effect of the resolution and the volume size (REV, representative ele- mentary volume analysis) on the computed porosity of apple samples. For comparison among cultivars, geomet- rical properties such as porosity, specific surface area, number of disconnected pore volumes and their distribu- tion parameters were extracted and analyzed in triplicate based on the 3D skeletonization of the pore space (medial axis analysis). The results showed that microtomography provides a resolution at the micrometer level to quantita- tively analyze and characterize the 3D topology of the pore space in apple tissue. The computed porosity was con- firmed to be highly dependent of the resolution used, and the minimum REV of the cortical flesh of apple fruit was estimated to be 1.3 mm 3 . Comparisons among the two cultivars using a resolution of 8.5 lm with a minimum REV cube showed that in spite of the complexity and variability of the pore space network observed in Jonagold and Braeburn apples, the extracted parameters from the medial axis were significantly different (P-value < 0.05). Medial axis parameters showed potential to differentiate the microstructure between the two evaluated apple culti- vars. Keywords Apple  3D image processing  Medial axis analysis  Microstructure  Representative elementary volume  X-ray microtomography Abbreviations CCD Charge-coupled device CT Computed tomography REV Representative elementary volume ROI Region of interest SSA Specific surface area STD Standard deviation 2D Two-dimensional 3D Three-dimensional Introduction The structural geometry of the pore space plays a funda- mental role in governing fluid and gas transport through any cellular tissue (Celia et al. 1995; Draz ˇeta et al. 2004). Particularly, in plant organs the gas-filled intercellular F. Mendoza (&)  P. Verboven  H. K. Mebatsion  B. Nicolaı ¨ BIOSYST, MeBioS, Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, W. de Croylaan 42, 3001 Leuven, Belgium e-mail: Bart.Nicolai@biw.kuleuven.be G. Kerckhofs  M. Wevers Materials Performance and Non-Destructive Evaluation, Department of Metallurgy and Materials Engineering (MTM), Katholieke Universiteit Leuven, Kastelpark Arenberg 44, 3001 Leuven, Belgium 123 Planta (2007) 226:559–570 DOI 10.1007/s00425-007-0504-4