Respiratory gas diffusivity mapping of horticultural product using X-ray CT
Tissue gas diffusion in a horticultural product is a microstructure-dependent process affecting the respiratory metabolism. As the porosity of the tissue varies across the product, it is likely that the effective gas diffusivity will be different at different positions. This study aims to develop a technique to construct a 3-D gas diffusivity map of the product based on X-ray CT images. Eggplant has been shown to have a wide range of porosity and was chosen to develop the technique. Relationships between effective oxygen (O2) diffusivity and porosity were determined for tissue samples at multiple radial positions. O2 diffusivity and porosity of the tissue were computed by solving a gas diffusion model on the 3-D tissue microstructure obtained by high resolution CT scans. Five different sizes of region of interest (ROI): 2.20, 1.33, 0.51, 0.13 and 0.01 mm3, were implemented to find out the best relationship between gas diffusivity and porosity. For the best correlation model, X-ray CT images of the product that had been previously translated into a 3-D porosity map were transformed to a gas diffusivity map. The predicted values were validated on separate samples with the actual gas diffusivity on the radial tissue. As a result, polynomial correlation models between effective O2 diffusivity and porosity were obtained (the highest R2=0.95). ROI sizes played an important role in determining the correlation. Complexity of the tissue microstructures influencing gas diffusivity such as tortuosity and connectivity of pores were likely minimized at the smaller ROI size, improving the correlation. The maps showed variations in O2 diffusivity (5.0×10‑11 NDASH 12×10‑6 m2 s‑1) in different cortex tissue regions of eggplant. Now, the O2 diffusivity map can be utilized as an input to study respiratory gas transports.
Nugraha, B., Verboven, P., Janssen, S. and Nicolaï, B.M. (2021). Respiratory gas diffusivity mapping of horticultural product using X-ray CT. Acta Hortic. 1311, 281-288
X-ray computed tomography, oxygen diffusivity, tissue microstructure, eggplant