Non-destructive characterization and volume estimation of pomegranate fruit external and internal morphological fractions using X-ray computed tomography

• X-ray computed tomography (CT) was used to characterise and quantify the internal structure of pomegranate fruit.
• X-ray CT accurately predicted fruit properties.
• X-ray CT is capable of estimating fruit volume and its fractions for in-line fruit quality systems.

In this study, X-ray computed tomography (CT) was used as a non-destructive technique to characterise and quantify the internal structure of pomegranate fruit (cv. Wonderful). A commercial X-ray system with a radiation source of 245 kW and electron current of 300 μA was used to generate two-dimensional (2D) radioscopic images which were reconstructed into three dimensional (3D) images for the quantification and volume estimation of internal structural components of fruit. Segmentation of the internal fruit components (arils, peel, kernel, juice content, air space) and single arils was achieved using StudioMax volume graphics software. The calculated volume of each fruit fraction were 162.5 ± 16.2, 163.9 ± 21.4, 16.4 ± 1.8, 10.9 ± 2.6 mL for arils, peel, kernel and air space, respectively which accounted for 48.1, 48.3, 4.9 and 4.1% of total fruit volume. Furthermore, the calculated volume of juice content was 146.1 ± 16.3 mL per fruit which was equivalent to an average of 89.8% of total aril weight, while a single aril (0.3 ± 0.04 mL) accounted for only 0.09% of whole fruit volume. Destructive validation measurements of each fruit fraction showed similar results to non-destructive data, with volumes of 163.3 ± 15.2, 161.8 ± 20.6, 15.1 ± 1.6, and 12.3 ± 4.4 mL for arils, peel, kernel, air space, respectively, while volumes of juice and single aril were 142.7 ± 16.4 and 0.3 ± 0.09 mL per fruit, respectively. Furthermore, the results showed that fruit physical attributes such as length, diameter and peel thickness were underestimated by an average of 0.14%, 1.13% and 5.27%, respectively, while fruit radius was overestimated by 1.75%. Nevertheless, no significant differences were observed for length, diameter, radius and peel thickness between X-ray CT predicted values and actual measurements. This work has demonstrated the capability of X-ray CT as a non-destructive technique to suitably estimate the fruit volume and its fractions which could be employed for fruit quality systems.