Abstract
Knowledge of the physical properties of date fruit is necessary for the design of postharvesting equipment such as cleaning, sorting, grading, kernel removing, and packing. Also, the physical and mechanical properties are incorporated in the development of the grading machine as a case study. In this study, some physical and mechanical properties of three mandarin cultivars, as promising fruits, were analyzed to help the design of handling machines. According to results, the greatest dimensional characteristics were found for Page cultivar, whereas Onsho cultivar showed the lowest sphericity value (93%), and the highest sphericity was observed in Clementine cultivar (97%). The specific gravity of Page cultivar was 0/97, and this cultivar had the biggest fruit. Thus, it may be used for export. The volume measured was 1% higher than the calculated assumed shape of the spheroid . The relationship between diameters and mass was linear, and the correlation was high for all studied cultivars and mixed cultivar (combined all data). There was a linear relation between mass and volume of the mixed cultivar of mandarin with a high coefficient of determination.
1. Introduction
Citrus are the major horticultural crops in Iran so that this country has a high annual production level of citrus fruit and was ranked the 15th producer in the world [1, 2]. The mandarin (Citrus reticulata) is a species of citrus fruit that is an evergreen tree (like other trees of this family) and slow growing. Mandarin begins to bear fruit when it is around three years old. Iranian mandarins are not exported because of variability in size and shape and lack of proper packaging [3]. Consumers prefer fruits with equal weight and uniform shape. Mass grading of fruit can reduce packaging and transportation costs and also may provide an optimum packaging configuration [4].
Fruit crops and food products have several unique characteristics which set them different from engineering materials. These properties determine the quality of the fruit, and identification of correlation among these properties makes quality control easier [5]. To design a machine for handling, cleaning, conveying, and storing, the physical, mechanical, and hydraulic properties of agricultural products must be known. Physical characteristics of fruit crops are the most important parameters to determine the proper standards of design of grading, conveying, processing, and packaging systems [6]. Among these physical characteristics, mass, volume, and projected area are the most important ones in determining sizing systems [7]. Information regarding dimensional attributes is used in describing fruit shape which is often necessary in horticultural research for a range of differing purposes including cultivar descriptions in applications for plant cultivar rights or cultivar registers [8, 9]. Quality differences in mandarin fruit can often be detected by differences in density. When mandarin fruits are transported hydraulically, the design of fluid velocity is related to both density and shape. Volumes and projected area of fruits must be known for accurate modeling of heat and mass transfer during cooling and drying [10]. Hydrodynamic properties are very important characters in hydraulic transport and handling as well as hydraulic sorting of fruit crops. To provide basic data essential for development of equipment for sorting and sizing mandarin, it should be determine several properties of this fruit such as fruit density and terminal velocity of that [11, 12]. Many studies have reported on the chemical, physical and mechanical properties of fruits, such as wild plum [13], rose fruit [14] and sweet orange [7]. Also, chemical, and physical and mechanical properties of fruits in mandarin were reported in several studies [15, 16], but limited studies concerning hydrodynamic, physiomechanical, and technological properties of Iranian mandarins have been performed. There are two main objectives for this study. The first is to determine the hydrodynamic and physiomechanical properties of three mandarin cultivars in Iran (Clementine, Onsho, and Page). The second is to produce a convenient reference table with hydrodynamical, physical, and mechanical information suitable for fresh mandarin mechanization and progressing.
2. Materials and Methods
Three mandarin cultivars in Iran consisted of Clementine, Onsho, and Page were used in this study. A total of 165 fruits (55 from each cultivar) were tested in the biophysical and biological laboratories. The mandarins were picked up at random from their storage piles. Fruit mass () was determined with an electronic balance with 0.01 g sensitivity. To determine the average size of the fruits, three linear dimensions, namely, as length, width, and thickness, were measured by using a digital caliber with 0.1 mm sensitivity. Volume () was determined by the water displacement method [17]. For this purpose, a mandarin was submerged into a known volume of water, and the volume of water displaced was measured. Water temperature was kept at 25°C. Specific gravity of each mandarin was calculated by the mass of mandarins in air divided by the mass of displaced water. Three mutually perpendicular axes, major, (the longest intercept), intermediate (the longest intercept normal to ), and minor, (the longest intercept normal to , ) of mandarin were measured by Win Area-Ut-06 meter (Figure 1) developed by Mirasheh [18]. Geometric mean diameter, GM, was determined from the cubic roots of three diameters, , and percentage sphericity was equal to the geometric mean diameter divided by the longest diameter multiplied by 100 as suggested by Mohsenin [17]. The volume of mandarins was calculated assuming the shape of a prolate spheroid, an oblate spheroid, and an ellipsoid applying the following equations, respectively, , , and (geometric mean diameter/2)3. An average projected area as a criterion for the sizing machine was proposed. Three mutually perpendicular areas, , , and were measured by a computer vision (diameter) Area-meter with high accuracy.
An average area projected (known as the criterion area, , cm2) was determined from
Spreadsheet software, Microsoft Excel, 2010, was used to analyse data and determine regression models between the parameters. A typical linear multiple regression model is shown in where is a dependent variable, for example, mass, , or a criterion area, , is volume, , , -independent variable, for example, physical dimensions (mm), or volume, , (cm3), -regression coefficients, -constant of regression. For example, mass is related to volume and can be estimated as a function of the volume measured as shown in where is the volume measured of mixed cultivars (combined all data) (cm3).
3. Result and Discussion
A summary of the physical, mechanical, and hydrodynamic properties of Clementine, Onsho, and Page cultivars is shown in Table 1. According to these results, the greatest dimensional characteristics were found for Page cultivar with means of 65.33, 64.15, and 56.33 mm major, intermediate, and minor, respectively, whereas these values were 61.45, 60.32, and 57.50 mm and 60.90, 59.83, and 49.11 mm for Clementine, and Onsho cultivars, respectively. Erodǧan et al. [19] reported that determining dimensional characteristics are essential to design a mechanism for mechanical harvesting.
An average of specific gravity of the Page cultivar was 0.97 and higher than others. The shape of studied cultivars is spheroid with a minimum probable error from the volume measured. Onsho cultivar showed the lowest sphericity value (93%) and the highest sphericity was observed in Clementine cultivar (97%). The specific gravity of Page cultivar was 0/97 and this cultivar had the biggest fruit. Thus, it may be used for export. Sphericity of mixed cultivar (combined all data) was 95%, and average of diameter of two diameters and was 1% less than the geometric mean diameter and with a similar coefficient of variation (8%). The knowledge related to geometric mean diameter would be valuable in designing the grading process [5]. The volume measured was 1% higher than the calculated assumed shape of the spheroid (). Volume and mass of each cultivar and also the mixed cultivar (combined all data) with three diameters were analyzed to determine the relationships between physical properties (Table 2). Result showed high relationship between volume and high coefficient of determination, , as shown in
Natural logarithm of volume with three diameters of all cultivars and mixed cultivar (combined all data) was high. The relationship between diameters and mass was linear, and the correlation was high for all studied cultivars and mixed cultivar (combined all data). Mass versus volume was plotted, and there was a linear relation between mass and volume of the mixed cultivar of mandarin with a high coefficient of determination, as shown in
Agamia et al. [20] reported that the average mass of fruit ranges from about 95 to 140 g, the fruit volume from 100 to 154 cm3, and the diameter from 4 to 6.5 cm for Nareng, Clementine, Satsuma, Cleopatra, Mallawi, and Baladi Mandarins. Mousa (1998) [2] found that the mean values of diameter ranged from about 69 to 84 mm; height ranged from about 57 to 87 mm; mass ranged from about 160 to 208 g; volume ranged from 188 to 241 mm for Navel, Baladi, Acidless, and Valencia orange varieties.
Relation between the mean projected area and the volume of mandarin was determined from the plot and the coefficient of determination, between both was very high and close to unity. A nonlinear regression equation for the mixed cultivar of mandarin was determined as showed in
Awady et al. [16] concluded that the physical properties of Minneola fruits which had oblong shape were as follows: diameter = 62–89 mm, height = 68–104 mm, mass = 201–345 g, volume = 120–342 cm3, and projected area = 54–108 cm2.
4. Conclusion
Some physical properties of Clementine, Onsho, and Page cultivars are presented in this study. From this study, it can be concluded that the highest and the lowest of length, geometric mean diameter, volume, mass, and specific gravity were obtained for Page cultivar, and it is the best for export. The lowest values for these traits were observed in Onsho cultivar. The mean percent sphericity of each mandarin cultivar resulted in different means, varying from 58.45 to 97.00%. Also, volume and diameter had a natural logarithmic relationship with three diameters. The physical and mechanical properties are incorporated in the design of the fruit hopper, revolving drums with holes (length and diameters of drums, diameter of holes, and number of holes), and exit chute of the designed grading machine.