The use of CT scan imaging technique to determine pear bruise level due to external loads

Abstract X‐ray computed tomography (CT) is an effective noninvasive tool to visualize fresh agricultural commodities’ internal components and quality attributes, also imaging via X‐ray CT is a non‐destructive and well‐developed method applied in measuring the internal effects of agricultural products. In the present research, 120 healthy pears with their health verification through the CT were selected. Next, 81 healthy pears were selected and subjected to quasi‐static and dynamic loading. The impact of the incoming pressures was investigated within 5, 10, and 15 days of storage. After loading and storing with the use of CT method, the total volume and the bruise volume of the pears were measured and the ratio of the bruise volume to the volume of each pear was calculated. Quasi‐static loads were pressurized over a period of two ways; the pressure of wide edge was exerted at three force levels of 70, 100, and 130 N while the pressure of the thin edge was applied at 15, 20, and 25 N. Dynamic loading was performed by utilizing a pendulum and 300, 350, and 400 g mass. The results of the experiments indicated that in the quasi‐static loading, the maximum and minimum amounts of pear bruise were 45.138% and 0.094% of the fruit, respectively. Besides, in the case of thin edge pressures, the minimum and maximum bruise levels were 0.007% and 19.88%, respectively. These values were obtained through 5 and 15 days of storage, respectively. In the dynamic loading, the maximum and minimum amounts of pear bruise were 47.36% and 0.21% of the total fruit, respectively, occurring at 400 and 300 g mass impact.

and analysis of fruits and reduce the losses as the product is not mechanically injured. Furthermore, by repeating the same measurements over time, more suitable results can be obtained from an agricultural product. An increase in consumer demand to ensure the quality of internal and external products and the interest in new industries resulted in the development of fast and cost-effective non-destructive tools for detecting and monitoring the fruit quality (Arendse, Fawole, Magwaza, & Opara, 2018). The use of CT and Xrays as non-destructive methods may allow checking the bruises on fruit (Diels et al., 2017). Pear (Pyrus communis L.), a valuable fruit, is consumed in various forms such as jam and is dried because of its special aroma and sweetness (Kolniak-Ostek, 2016;Pérez-Jiménez & Saura-Calixto, 2015). It contains considerable amounts of sugar, vitamins, organic acids, polyphenols, minerals, and other nutrients.
Free sugars, organic acids, free amino acids and fatty acids, minerals, and perfumes are natural components of many fruits and vegetables and they play important roles in preserving the quality of the fruit and determining its value (Chen, Wang, Wu, Wang, & Hu, 2007;Yi et al., 2016). Moreover, consuming healthy fruits reduces the risk of chronic illness as they contain numerous antioxidants (Qu, Zhao, Zhao, Liu, & Yang, 2016). Mechanical damage to fruits is mainly caused during the harvest operations; however, in packaging and sorting stages, during transportation, and in the consumer market, retailers and consumers pose mechanical damage to the fruits that can reduce their quality (Li & Thomas, 2014;Opara & Fadiji, 2018).
Mechanical damages result in economic losses. In order to minimize these losses, certain studies are conducted to investigate the impact loading and quasi-static loading conditions during and after harvesting fruits, vegetables, and other biological materials (Stropek & Gołacki, 2015). Some researchers asserted that a slight impact force may not entail any changes in the fruit. On the other hand, when you see a portion of the fruit damage during a physical injury, there is obviously a significant bruise during the warehousing process. Physical evidence also includes cell fractures and color changes in the desired fruit that occur when each cell is squeezed. Such damages eventually ruin the fruit and change its color (Opara & Pathare, 2014).
Several attempts are made to find the suitable methods for assessing the qualitative characteristics of agricultural and food products without any destructive consequences. Advanced technology has broadened the horizon to determine the quality of non-destructive nutrients through some techniques such as X-ray imaging, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound techniques (Kotwaliwale et al., 2014). Razavi, Asghari, Azadbakh, and Shamsabadi (2018) applied MRI technique by following a static loading in order to assess the pear bruise and found that time and force, both individually and simultaneously, have a significant effect on the bruise volume. They also reported that the best time to consume pear after loading, discharge, and internal bruises during harvesting and storage is 12 days. Kim, Kim, Park, Kim, and Cho (2014) indicated that infrared lock-in thermography and the information it provides are of great assistance to detect the mechanical damage to the fruit, particularly in the early stages of bruising. Zhang, Cui, and Ying (2014) employed a vibratory acoustic non-destructive measurement in order to investigate pear tissue. They selected three tissue indexes (MF, FF, and Stiff) and seven vibration parameters (F2, A2, P400, P800, P1200, P1600, and EI) from the samples. They indicated that, compared with MF and FF, Stif is a more proper indicator of the evaluation of the qualities of the fruit and is well correlated with the vibrational parameters. They also expressed that the multiple vibration parameters provided more information for predicting the tissue by the unit vibration parameter. Following correction via SI, the performance of the prediction model was improved. The results of the experiments revealed the significance of both the original and modified prediction models. Furthermore, the evaluation of pear tissue was combined with the LDV method which rendered the proposed modeling feasibly. Muziri et al. (2016) studied microscopic analysis and tissue detection in pears by employing X-ray computed tomography and confirmed that the tissue of crispy fruits is more porous than non-crispy ones. They further provided evidence regarding the formation of lysigenous masses in crispy pears and indicated that these fruits are larger and more oval while non-crispy fruit cells are more spherical.
In their study on bruises in apples, Diels et al. (2017) applied a computerized X-ray tomography and reported the bruises created by a spherical impactor (pendulum) using the buccal visualization in all 2D and 3D images. This bruise can be highly irregular, suggesting that the estimates of bruises based on simple geometric hypotheses cannot provide accurate results.
During transportation, the pear is placed under the two pressures of wide edge (from pears, vehicles, Pear box etc.) and thin edge pressure (pedicle a pear on another pear, the sharp side of the pear box, etc.), as well as the possibility of being under the impact load (when picking from the tree, sorting machines, etc.). In the current paper, these loading forces are simulated to determine the rate of pear bruises after loading and storage. The present research was conducted to evaluate pear bruises by quasi-static and dynamic loading over different periods using CT in a way to calculate the storage time of pear fruit. It was indicated that through appropriate measures, post-harvest problems such as bruises and economic losses can be reduced prior to, during, and following the harvest.

| Sample preparation
The Pears (Spadana variety( were purchased from gardens around Gorgan, Golestan province, Iran. Samples were placed in separate boxes, and inside the boxes, pears were at a distance from each other.
The life of the pear tree used in this research was 5 years old. The days after full bloom was about 120 day, and the pears were freshly harvested and the experiments were carried out as quickly as possible.
Then Samples were taken to the laboratory of Gorgan University of Agricultural Sciences and Natural Resources. They were placed in an oven and their moisture contents were measured (Azadbakht, Torshizi, Ghajarjazi, & Ziaratban, 2016). The calculated moisture content of the pears was 77.92%. Environmental conditions for testing were conducted at a temperature of 18°C and relative humidity of 72%.

| Quasi-Static test
In order to perform the wide and thin edge compression mechanical test,

| Pear preparation for imaging
In the present experiment, 120 pears were selected based on a nondestructive CT scan. Next, 81 pears without any bruises were selected.
Following the dynamic and quasi-static loading, the pears were stored for 5, 10, and 15 days. The storage conditions were similar to those of sale centers so that the fruits could be studied during storage and consumption.
The ambient temperature was 14°C and the relative humidity was 66%.

| Imaging via CT scan method
To perform the imaging, pears were taken to the test site and inserted into the CT scan crate after starting CT scan through the control room round the pears in a series of turns to create the image. Also, the pitch was locked for the test; that is, pitch 1. Images were recorded F I G U R E 3 CT scan imaging process. 1-Control Room; 2-Send information and Setting Device; 3-Pear sample; 4-X-rays tube; 5-X-ray input; 6-X-ray outlet from sample; 7-Crystals CT Scan; 8-Converted to image codes F I G U R E 4 The CT Scan device used in the research F I G U R E 5 CT scan imaging process. There are 1-9 steps in creating the image, 1 first image and 9 final images at 80 kV and 120 mAh current, and 1 mm slices were used to create full images. The images created by the Syngo CT 2012 software were recorded and extracted in the form of two-dimensional and grayscale images. Convolution kernel, which demonstrates image resolution level, was B31Smooth and the images were created by 512 × 512 matrixes. Figure 4 illustrates the CT scan used in this experiment.
An interval was applied between bruises and imaging in order to allow the bruises to reduce their moisture content and be better fixed on the fruit. Such a difference in moisture can increase the absorption of X-rays between healthy and unhealthy texture (Diels et al., 2017).
Subsequently, using the data obtained by the device, the total volume, bruise volume of each fruit, and the two-dimensional color images of each bruise were measured; the ratio of bruises to the total volume of each pear was obtained by CT scan and was recorded with loading time in the Excel software. Furthermore, during the imaging of each pear, 70-100 images on average were captured to achieve the full-size pears for 3D reconstruction. The steps involved in this process for each image are indicated in Figure 5. A redesigned two-dimensional image of the pear is also depicted in Figure 6, which can be divided into healthy texture and rotten texture. In Figure 5, No. 1 and No. 2 present the bruise location and the image created by the CT scan, respectively.

| Statistical analysis
Samples were stored for 5, 10, and 15 days after quasi-static and dynamic loading, followed by the imaging process. All the experiments were performed in three replications and the results were analyzed by employing a factorial experiment in a completely randomized design with SAS statistical software.

| The effect of wide edge pressure on bruise percentage
As illustrated in Table 1

| The effect of thin edge pressure on bruise percentage
According to Table 1, the thin edge pressure in the storage periods and the loading force is significant at 1% level. Moreover, Figure 8 indicates the significance of its interaction. Considering the results of the constant loading force, an increase in the storage period leads to a corresponding rise in the bruise percentage in pears. Similarly, under a constant storage period, the increase in the loading force augmented the percentage of the bruise. The highest and lowest bruise percentages were 19.880% and 0.007%, respectively, belonging to the 15-and 5-days storage periods, and 25 and 5 N loading pressures.

| The effect of impact on bruise levels
Based on Table 1, the impact mode is significant in terms of storage and loading force at 1% level. Figure 9 illustrates the significance of its interaction effect. At a constant loading force, as the storage period increased, the bruise percentage is increased. Similarly, in a constant storage period, bruise percentage increased with the rise in the loading force. The highest and lowest percentages of bruises were 47.36 and 0.21, respectively, occurring in 15 and 5 days into the storage and under 400 and 300 g mass.
The current results revealed that the mass of 400 g created the highest pressure in the present study. Needless to say, the bruises were higher under these pears compared with the other two masses. the presence of bruises on the newly-harvested products affects certain physiological processes remarkably, which is acknowledged as the moisture breathing through the injured skin. In particular, the changes in metabolic processes such as ethylene production, relative electrical conductivity, respiration, and transpiration, more than often, result in a mass loss, aging, corruption, and loss of nutritional value (Hussein, Fawole, & Opara, 2018). These results are in accordance with that of Komarnicki, Stopa, Szyjewicz, and Młotek (2016) on the bruise resistance of pear against impact.
They reported that bruises were not visible in small loads; however, they became more and more visible with an increase in the load (Komarnicki et al., 2016). Also, Ahmadi, Ghassemzadeh, Sadeghi, Moghaddam, and Neshat (2010)

| CON CLUS IONS
• When a pear is affected by wide edge (pear-to-pear) pressure in the shipping box, or in the store or fruit shop, it is best to be utilized within 6-9 days. Wide edge pressures of 70, 100, and 130 N, which are increased in the storage period from 5 to 10 days, lead to bruis- • If a pear is affected by an impact from falling down a tree or human treatment, it is best to be used in <15 days. With the increase in the storage period from 5 to 10 days, the bruise percentages at 300, 350, and 400 g loading pressures were 8.79, 1.08, and 2.95, respectively. From 10 to 15 days, increasing the storage days augmented the bruise rates by 2.32, 2.37, and 1.19 times at 300, 350, and 400 g mass, respectively. In the storage periods of 5, 10, and 15 days, for 300-350 g, the bruises were 22.66%, 2.78%, and 2.84%, and for 350-400 g, the bruise rates were 2.81, 7.68, and 387 times, respectively.
• According to the results, the quasi-static loading has a greater effect on the bruise levels in pears and the highest effect of loading belongs to the wide edge pressure. Also, the best storage period is 5 days during which the pears are least affected regarding their quality. From 10 days onward, no significant change is observed in the bruises with the passage of time.