Three-dimensional pore space quantification of apple tissue using X-ray computed microtomography

Department of Metallurgy and Materials Engineering, University of Leuven, Louvain, Flanders, Belgium
Planta (Impact Factor: 3.26). 08/2007; 226(3):559-70. DOI: 10.1007/s00425-007-0504-4
Source: PubMed


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 quantitatively 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 elementary volume analysis) on the computed porosity of apple samples. For comparison among cultivars, geometrical properties such as porosity, specific surface area, number of disconnected pore volumes and their distribution 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 quantitatively analyze and characterize the 3D topology of the pore space in apple tissue. The computed porosity was confirmed 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 mum 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 cultivars.

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Available from: Fernando A Mendoza, Sep 09, 2014
    • "This technique can help to characterise and understand foods by measuring cell size and shape, void space and spatial distribution (Lim and Barigou, 2004). The use of CT has allowed visualisation of the fruit void network architecture , showing a volume fraction of 5.1% and 23% for 'Conference' pear and 'Jonagold' apple cortex tissue, respectively (Verboven et al., 2008; Mendoza et al., 2007). This technique was also successfully used in 3-D analysis of raphides in rose peduncles and Lotus miyakojimae seeds (Matsushima et al., 2012; Yamauchi et al., 2013). "
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    ABSTRACT: Pre-harvest growing conditions during the development of fruit have impacts on fruit quality at the time of harvest and during storage. These impacts may result in differences in the skin properties of the fruit and some sub-surface cellular structural changes, which have potential effects on postharvest fruit quality and storability. Optical coherence tomography (OCT) is a non-destructive imaging method that enables acquisition of three-dimensional (3D) images of sub-surface structures of semi-transparent and turbid objects. This technology is a potential tool to provide new information about the structural nature of horticulture products. This work used five commercial kiwifruit cultivars, 'G3', 'G9', 'G14', 'Hort16A' and 'Hayward', where 'Hayward' was also manipulated with different orchard management practices (crop load and girdling), to investigate the properties of the layers of structures immediately underneath the periderm. Fruit samples were harvested at commercial maturity and then 3D OCT images of the skins were captured prior to fruit quality assessment. An automated image processing protocol was established to enable visualisation and characterisation of larger near skin cellular structures in the outer parenchyma tissue. There was no obvious differentiation between the observed large cells and the stone cells that are present in Actinidia chinensis cultivars. Significant differences in the microstructures of the sub-surface cells were found amongst five commercial kiwifruit cultivars. In general 'G3', 'G14' and 'Hayward' had larger and greater numbers of large sub-surface cells than 'G9' and 'Hort16A'. The volume fraction of large cells in the near skin tissue was lower for the yellow-fleshed cultivars ('G3', 'G9' and 'Hort16A') in comparison to the green-fleshed cultivars ('G14' and 'Hayward'). Low crop load increased maximum large cell length. However, no other effects of crop load and girdling were observed on the microstructures of the large cells in 'Hayward'. Overall, OCT was an efficient non-destructive technique that can be utilised to reveal the structures of skin and sub-surface cellular layers with high resolution. The developed image processing protocol was suitable for the processing of large data sets with acceptable accuracy. However, more work should be carried out to overcome image artefacts caused by surface lenticels and trichomes. Limitations caused by low penetration depth should also be improved to allow better representation of the whole fruit structure.
    No preview · Article · Dec 2015 · Postharvest Biology and Technology
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    • "Hereby also 6 to 7 cell layers were excluded to remove damaged cells at the edge as a result of cutting the samples. The remaining prismatic volume measured 2.1 x 2.1 x 3.1 mm 3 , a volume which was found representative of cortex tissue [19]. The cells in the fruit cortex tissue could be readily segmented from the intercellular airspace by means of Otsu thresholding [48] because of the excellent contrast between the two distinct regions in the images. "
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    ABSTRACT: 3D high-resolution X-ray imaging methods have emerged over the last years for visualising the anatomy of tissue samples without substantial sample preparation. Quantitative analysis of cells and intercellular spaces in these images has, however, been difficult and was largely based on manual image processing. We present here an automated procedure for processing high-resolution X-ray images of parenchyma tissues of apple (Malus × domestica Borkh.) and pear (Pyrus communis L.) as a rapid objective method for characterizing 3D plant tissue anatomy at the level of single cells and intercellular spaces. We isolated neighboring cells in 3D images of apple and pear cortex tissues, and constructed a virtual sieve to discard incorrectly segmented cell particles or unseparated clumps of cells. Void networks were stripped down until their essential connectivity features remained. Statistical analysis of structural parameters showed significant differences between genotypes in the void and cell networks that relate to differences in aeration properties of the tissues. A new model for effective oxygen diffusivity of parenchyma tissue is proposed that not only accounts for the tortuosity of interconnected voids, but also for significant diffusion across cells where the void network is not connected. This will significantly aid interpretation and analysis of future tissue aeration studies. The automated image analysis methodology will also support pheno- and genotyping studies where the 3D tissue anatomy plays a role.
    Full-text · Article · Dec 2015 · BMC Plant Biology
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    • "New tomographic imaging methods enable a thorough update of the blueprints of these long known transport pathways and how they develop during fruit growth. X-ray micro-Computed Tomography (µCT) has been employed to visualize and characterize voids in a variety of fleshy fruit tissue samples such as cucumber (Kuroki et al., 2004), pome fruit (Mendoza et al., 2007; Verboven et al., 2008), mango (Cantre et al., 2014b), and kiwi (Cantre et al., 2014a). X-ray µCT is likely the most appropriate technique to study voids in 3D as it provides a relatively large contrast between air and cells even for high resolutions (as low as 1 µm and beyond). "
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    ABSTRACT: The void network and vascular system are important pathways for the transport of gases, water and solutes in apple fruit (Malus × domestica Borkh). Here we used X-ray micro-tomography at various spatial resolutions to investigate the growth of these transport structures in 3D during fruit development of "Jonagold" apple. The size of the void space and porosity in the cortex tissue increased considerably. In the core tissue, the porosity was consistently lower, and seemed to decrease toward the end of the maturation period. The voids in the core were more narrow and fragmented than the voids in the cortex. Both the void network in the core and in the cortex changed significantly in terms of void morphology. An automated segmentation protocol underestimated the total vasculature length by 9-12% in comparison to manually processed images. Vascular networks increased in length from a total of 5 m at 9 weeks after full bloom, to more than 20 m corresponding to 5 cm of vascular tissue per cubic centimeter of apple tissue. A high degree of branching in both the void network and vascular system and a complex three-dimensional pattern was observed across the whole fruit. The 3D visualizations of the transport structures may be useful for numerical modeling of organ growth and transport processes in fruit.
    Full-text · Article · Sep 2015 · Frontiers in Plant Science
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