Mechanical property evaluation of apricot fruits under quasi-static and dynamic loading

Abstract

Introduction: Some forces and impacts that occur during transporting and handling can reduce the apricot quality. Bruise damage is a major cause of fruit quality loss. Bruises occur under dynamic and static loading when stress induced in the fruit exceeds the failure stress of the fruit tissue. Needless to say that physical and mechanical properties of fruits in the design and optimization of systems related to production, processing and packaging of the products are important. Harvesting, transport, packaging and transportation of fruits and vegetables, result in their bruising which can cause loss of marketability of the fruit by consumers. The term of ‘absorbed energy’ could be used to express the quantity of damage done on the fruit and the high the absorbed energy, the higher the damage on the fruit. The object of this research was due to the importance of apricot fruit and lack of information about the mechanical behavior. Materials and Methods: In this study, apricot fruit variety “Ziaolmolki” was examined to determine some physical and mechanical properties. In order avoid any damage, the fruits were carefully harvested from trees and gathered in plastic boxes in a row, to prevent damage to the apricots. For determination of mechanical properties and levels of impact energy used test axial machine and pendulum device, respectively. Dependent variables (acoustics stiffness, radius of curvature, color characteristic a* and b*, Brix percentage, penetration force, penetration work and penetration deformation) and independent variables (impact energy in three levels, temperature and color in 2 levels each) were selected and analyzed by block designs with factorial structure. In the experimental design, the fruits were stored in two temperature levels, 3oC and 25oC. Two areas of any fruit (red and yellow areas) were subjected to 3 impact energy levels. For each of the 8 levels, 8 fruit samples were selected. Overall, 96 fruits {8 (number of fruit per level) × 3 (impact energy level) × 2 (both red and yellow) × 2 (at 25oC and 3oC)} was selected. In this study, using a factorial experiment in a completely randomized design, the effect of different factors (impact energy in 3 levels, temperature in 2 levels 3oC and 25°C and color in 2 levels red and yellow) on acoustic stiffness, radius of curvature, color characteristic a* and b*, precent Brix, penetration force, penetration work and penetration deformation in apricot under the quasi-static forces were studied. In order to conduct this experiment, the universal testing machine of biological materials was used. After the determination of mechanical properties of the products, the SAS statistical program (1.9) was applied to analyze and normalize the resulted data. Factorial test also was used to determine the effects of independent variables on the dependent variables. Data analyses were performed using Statistical Package for the Social Sciences (SAS version 19.0).The variance analysis of the data was conducted in the form of multivariate factorial (2×2×3) design. The data were collected by three controlling factors: two temperature levels (3 and 20°C), two types of colour (Yellow and Red fruits) and three levels of impact energy. The Duncan’s multiple range tests was used to compare the means. The values of reducible sugars were measured by the fruit juice standard - test methods No. 2685 (Institute of Standards and Industrial Research of Iran). The apricots TSS (total soluble solids) for each temperature level by Refractomete (Model: 3820 (PAL-2), Resolution: ± 0.1% Brix) were obtained. Results and Discussion: Respectively, the main and interaction effects of these variables were examined. The results of analysis of variance showed that,, the radius of curvature, color characteristic, acoustics stiffness, elastic modulus, percent Brix, penetration force and penetration deformation on main and interaction effects were significant at 5% and 1% probability level. According to the analysis of variance table between dependent and independent parameters, a significant effect was observed. Increasing impact energy, the penetration force and penetration deformation at 3°C was higher than at 25°C (Fig.3, 4, 7 and 8). Increasing impact energy, the red zone showed more penetration deformation and penetration force than the yellow zone (Fig.5 and 6). In a constant level of energy the higher the temperature of fruit tissue, the more energy is absorbed, due to this fact that lower temperatures can increase stiffness of the fruit, and leads to transport of absorbed energy to inside the tissue and increase the fruit bruising and final results in less needed penetration force for fruit transformation. Apricot acoustic stiffness in the temperature of 3oC was higher than in the temperature 25oC (Table 3). Fruit stiffness and tissue viscosity increases with increasing temperature. With increasing tissue stiffness, the less impact energy is absorbed and less bruising in fruit tissue is created. Because of more tissue stiffness, in order to create penetration in fruit tissue the more transformation is needed. Conclusions: The red zone showed a higher bruise susceptibility of ripe apricots. According to the analysis of variance table between dependent and independent parameters, a significant effect was observed. Increasing impact energy, the penetration force and penetration deformation at 3°C was higher than at 25°C. Increasing impact energy, the red zone showed more penetration deformation and penetration force than the yellow zone. Apricot acoustic stiffness in the temperature of 3 oC was higher than in the temperature 25oC.

Keywords

• apricots
• color
• impact energy
• pendulum
• temperature