Determination of physical and mechanical properties of carrot in order to reduce waste during harvesting and post‐harvesting

Abstract Lack of sufficient knowledge about the physical and mechanical properties of agricultural products can result in higher waste of them. Due to the importance of carrot as an agricultural product and lack of much knowledge about how to reduce its waste as well as design and optimize the required harvest and postharvest machinery, this research study was carried out to fill this gap. In this study, physical properties included the length, width, thickness, mean diameter (geometric and arithmetic), mass, volume, density, sphericity, surface area, aspect ratio. The mechanical properties of the samples and their lengths were measured under the conditions of pressure (bruise), bending (break), and shearing of the carrot halves using a Zwick/Roell Instron testing machine based on the recommended standards. The mean geometric mean diameter, surface area, sphericity, volume and true density of the carrot were 49.54 mm, 7758.32 mm2, 0.32%, 70 cm3, and 1.04 g/cm3. In the study of mechanical properties of carrots, the maximum forces required for bruising, bending, and shearing of the carrot fruit were 71.90, 48.60, and 41.14 N, respectively. The results obtained about the physical and mechanical properties can be very useful in reducing carrot waste and mechanizing harvest and postharvest operations by providing us with information that helps us design machinery needed to transfer, sort, separate, wash, package, store, and process carrots.

get bruised due to the pressure on them that is caused by heavy loads. Such damages reduce the quality of the product and increase the waste rate (Akbarnejad et al., 2017;Jaliliantabar, Lorestani, Gholami, Behzadi, & Fereidoni, 2011;Rong, Qunying, & Deqiang, 2004). Processing and proper transportation techniques for agricultural products require precise data regarding the physical properties of them such as the shape, size, porosity, surface area, and density (Jahanbakhshi, Yeganeh, & Akhoundzadeh Yamchi, 2016;Topuz, Topakci, Canakci, Akinci, & Ozdemir, 2005). Density and porosity affect the structural loads and are considered as important parameters in designing storage and drying systems (Mpotokwane, Gaditlhatlhelwe, Sebaka, & Jideani, 2008). Stiffness parameters can be used as indexes for the vulnerability of the agricultural products. Weight, volume, density, and average geometric diameter are the factors used to describe agricultural products (Goyal, Kingsly, Kumar, & Walia, 2007;Jahanbakhshi et al., 2016). Rasekh and Majdi (2012) studied the mechanical properties of garlic. They reported that the forces necessary to loosen the garlic bulbs when loading them along the height and in the lateral yield were 127.023 to 228.001 N and 45.52 to 106.97 N respectively. Kılıçkan and Güner (2008) studied physical and mechanical properties of olive fruit under compressive loading. They showed that the special deformation and rupture energy changes significantly increased as with increase in size and deformation rate and the highest values of change took place along the longitudinal dimension. Rasekh (2014) investigated some mechanical properties of black-eyed peas and reported that moisture had a significant effect on all mechanical properties at 1% probability level. In addition, he stated that increase in moisture would increase the amount of the energy required for rupture, toughness and deformation at the point of rupture increased while the required force for rupture decreased.
The aim of this study is to determine some mechanical properties of carrot fruit. The results of the research will be very useful in designing different devices in the processes of production to supply the product with reduced waste and damage.

| Determination of physical properties
In this study, the carrots which were at the full ripeness level were collected. Then, any external material and premature or damaged carrots were taken away. To prevent the product from losing its initial moisture, the samples were kept in a refrigerator at the temperature of 4 ± 1°C and about two hours before the experiments.
To reach the room temperature, the samples transferred from the storage space (the refrigerator) to the laboratory. To do so, 20 g carrot samples were placed inside the oven for four hours at the temperature of 105°C in three replications (Doymaz, 2007;Jahanbakhshi et al., 2016). To measure the weight of the samples before and after being placed in the oven, a digital scale (GF600, USA model) with the accuracy of 0.01 g was used. Then, the moisture content and dry matter of carrot fruit were calculated by Equations (1) and (2), respectively (Moghadam & Kheiralipour, 2015): where, MC is the moisture content of fruit (%), M w is the initial mass of fruit (g), M d is the mass of dried fruit (g), and DM is the dry matter fruit (%).
The means for the moisture content and the dry matter of carrot fruit were 87.18% and 12.82%. The properties of carrots were measured at their initial natural moisture. To measure physical properties, 100 samples of carrot were selected randomly.
Dimensions of the carrot (their length (L), width (W), and thickness (T)) were measured using a DC-515, Taiwan digital caliper with the precision of 0.01 mm. Then, the geometric mean diameter, arithmetic mean diameter, and sphericity were calculated through Equations 3, 4, and 5. D g is the geometric mean diameter, D a is the arithmetic mean diameter and Ø is the sphericity of the carrot. The surface area (S) and the aspect ratio (R a ) of the carrot were obtained through Equations 6 and 7.
The carrots mass was measured using a GF600, USA digital scale with the precision of 0.01 g. To determine the volume of the carrots, the platform method was used (Mohsenin, 1986). Thus, the samples were dipped in a beaker that was placed on a scale using a legged clamp. The second reading of the scale showed the weight of the fruit dipped into the water minus the weight of the container and the water which equaled the weight of the displaced water. This weight is inserted into the following and the volume of the carrots is calculated through Equation 8.
The density of the carrots is obtained by Equation 9. where W w is the density of the displaced water (g/cm 3 ), ρ W is the density of the water (g/cm 3 ), ρ t is the true density (g/cm 3 ), M is the mass (g), and V is the volume of the carrots (m 3 ).

| Determination of mechanical properties
In order to determine the mechanical properties of the carrot fruit  (Jahanbakhshi, 2018;Jahanbakhshi et al., 2016;Jaliliantabar et al., 2011). The Instron machine was simultaneously connected to a computer and data mining was carried out. An example of the graphs, related to the bruise, bending and shearing tests, is shown in Figure 1.

| Physical properties
The amounts physical properties of carrots are shown in Table 1. Packaging must take into account the requirements of transportation and marketing in terms of the weight, size and shape of the agricultural products. The information obtained in this research can be used in this regard. Since the length of the carrot has a great difference with its width and thickness, it can be concluded that carrot has a low sphericity (0.32%) and this property must be taken into consideration in designing transfer, handling, and grading systems. The true density of the carrot was 1.

| CON CLUS ION
1. In addition to the importance of studying physical and mechanical properties in minimizing mechanical damage, these properties are considered as the basic data in designing the machinery and equipment used during the harvesting and in the postharvesting operations.

2.
In examining mechanical properties, the maximum force required in bruising, bending and shearing tests of the carrot fruit were 71.90, 48.60, and 41.14 N respectively.

3.
In comparison to the shear module obtained in previous studies, the high shear module for carrot fruit in this study (0.00324 N/ mm 2 ) shows its high resistance against shear strain.

ACK N OWLED G EM ENTS
The authors thank Department of Biosystems Engineering, University of Mohaghegh Ardabili for partial support of this study.

CO N FLI C T O F I NTE R E S T
The authors have declared no conflict of interest.

E TH I C A L R E V I E W
This study does not involve any human or animal testing.