Post-harvest technologies
A. Khalaj; E. Ahmadi; S. Mirzaei; F. Ghaemizadeh; R. Abbaszadeh
Abstract
IntroductionGrape is a major horticultural crop with a high nutritional value in the world. The optimal geographic and climatic conditions in Iran have positioned it as one of the most important regions for grape cultivation in the world. Black rot, caused by Aspergillus niger, is a highly destructive ...
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IntroductionGrape is a major horticultural crop with a high nutritional value in the world. The optimal geographic and climatic conditions in Iran have positioned it as one of the most important regions for grape cultivation in the world. Black rot, caused by Aspergillus niger, is a highly destructive fungal disease that affects the grapes by targeting wounded areas. It causes crushing of the grapes, the falling of berries, and reduces transportation and storage properties (Ponsone et al., 2011). Various methods, such as fumigating bunches with sulfur dioxide and storing them in a modified atmosphere, have been used to control fungal rot and prolong the shelf life of grapes. However, each method has its limitations. Grape fumigation with sulfur gas is harmful to human health (Duarte-Sierra et al., 2016) and the efficiency of modified atmospheric storage on rot control and maintaining the quality of grapes depends on the type of variety, storage temperature, and especially gas concentration (Himelrick, 2003).Given the lack of efficiency in traditional methods, it is imperative to introduce modern techniques that can effectively disinfect microorganisms. These advanced methods offer several advantages, including the preservation of crop quality, an increase in crop shelf life, the promotion of good health, and substantial economic benefits. A technique of this type includes using non-thermal (cold) plasma (NTP) technology to eliminate food microorganisms (Bourke et al., 2018). The effect of cold plasma at atmospheric pressure on the reduction of bacterial populations in food products such as lettuce, tomato, strawberry, and cherry tomato has been reported (Bermúdez-Aguirre et al., 2013; Pasquali et al., 2016; Ziuzina et al., 2014). Research has shown that cold plasma can effectively inactivate Aspergillus in various orchard and agricultural products (Butscher et al., 2016; Ghorashi et al., 2020; Selcuk et al., 2008). The effect of cold plasma on the quality characteristics of the product during the post-harvest period has also been investigated. Blueberries treated with cold plasma for less than 15 minutes showed remarkable results: after 10 days, the fruit exhibited reduced lipid peroxidation and darkening, with no impact on the total anthocyanin content, pH, or firmness of the product (Hu et al., 2021). In a study by Rana et al. (2020), it was found that subjecting strawberries to 15 minutes of cold plasma with packaging after 5 days of storage at 25°C had no significant impact on pH, TSS, and moisture content of the fruit.The review of the literature reveals the absence of research on fungal disease control and grape quality evaluation following the use of NTP. This study aims to investigate the efficiency of plasma treatment in reducing the infection with Aspergillus fungi, along with examining the physical, chemical, and mechanical properties of Fakhri grape.Materials and MethodsThis research was conducted as a completely randomized design in a factorial experiment at four plasma levels (0, 10, 20, and 40 s) and five storage periods (1, 2, 3, 4, and 5 weeks) with three replications at 4°C. A plasma generator was first designed and manufactured in this study. A specifically designed and fabricated plasma application probe was also developed for grape berries. The individual grape berries were then sterilized with 1% sodium hypochlorite under a laminar hood for 2 minutes. Afterward, they were rinsed three times with sterile distilled water to remove any remaining disinfectant residue from their surfaces. Sterilized berries were immersed in Aspergillus spore suspension with 105 spores.ml-1 concentration. Finally, all samples were dried on paper filters and prepared for different plasma treatment durations (0, 10, 20, and 40 s). The treated samples were stored at 4°C, and the infection percentage and microbial load were measured on a weekly basis. To assess the preservation quality, chemical parameters such as pH, TSS, and TA, physical parameters (color change and weight loss), and mechanical properties were measured every week. Additionally, thermal imaging was performed weekly.Results and DiscussionPlasma application during storage significantly reduced the infection percentage and microbial load in Aspergillus-inoculated samples. At the end of the storage period, the infection percentage and microbial load in the 40-second plasma treatment were 5% and 2.5 CFU g-1 respectively, while in the control group, the infection percentage was 100% and the microbial load was 4 CFU g-1. At the end of the storage period, the lowest pH level in the plasma was observed for 40 s plasma. This could be attributed to effective contamination control, as fungal contamination leads to alkalization of the environment. The highest amount of TSS was also observed in control and 40 s plasma. But in the 10 and 20 s plasma treatment, the process of changes was gradual and not significant. The higher TSS level of control and 40 s plasma can be due to the weight loss caused by the spread of contamination and moisture leakage caused by damage to the tissue. This decrease in moisture leads to an apparent increase in the TSS index. Research has shown that plasma primarily affects the surface characteristics of products, and when applied with the appropriate voltage and duration, it does not alter the internal chemical properties (Hu et al., 2021). Over time, weight loss increased in all treatments. This increasing trend during the storage period is higher in control and 40 s plasma compared to 10 and 20 s plasma. Therefore, the weight loss in the control can be due to the spread of contamination and aging of the product over time. However, the weight loss in the 40-second plasma treatment can be due to the destruction of the fruit tissue caused by longer duration of the plasma application.In the current research, by increasing the duration of plasma application to 40 s, a significant decrease in L*, a*, and b* indices and an overall change in the color of the product was observed. Research shows that in blueberries, inappropriate duration of plasma treatment causes the loss of wax on the fruit surface and leads to darkening of the product (Hu et al., 2021). The highest and lowest changes in temperature drop were observed in the control treatment (5°C) and 10 and 20 s plasma (3 and 3.5°C, respectively). According to research, an increase in fungal contamination leads to a decrease in humidity, increases weight loss, and subsequently a decrease in product temperature. A decline in mechanical characteristics was noted for the control and plasma treated samples during the storage period. The lowest value for indicators was observed in the 40 s plasma treatment. However, no significant difference was observed in samples treated with plasma for less than 20 seconds compared to the control group up to the middle of the storage period. According to a report by Misra et al. (2014), plasma application can reduce tissue softness. Therefore, optimizing its plasma duration and intensity is very important (Pan et al., 2021). ConclusionOur experiments aimed to investigate the effect of NTP treatment on controlling Aspergillus infections while preserving the quality properties of Fakhri grapes. The obtained results are important for two main reasons. Firstly, an innovative probe was designed for plasma applications, specifically tailored to the shape and size of individual grapes in order to thoroughly cover them with plasma. Secondly, application of plasma was carried out for the first time and yielded valuable results, indicating that this technique can control fungal infections and preserve the chemical, physical, and mechanical properties of grapes.
Post-harvest technologies
V. Kahrizi; E. Ahmadi; A. R. Shoshtari
Abstract
IntroductionThe growing consumer demand for high-quality products has led to the development of new technologies for assessing the quality of agricultural products. Iran is the 9th largest orange producer in the world. Every year, large quantities of agricultural products lose their optimal quality due ...
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IntroductionThe growing consumer demand for high-quality products has led to the development of new technologies for assessing the quality of agricultural products. Iran is the 9th largest orange producer in the world. Every year, large quantities of agricultural products lose their optimal quality due to mechanical and physical damage during various operations such as harvesting, packaging, transportation, sorting, processing, and storage. This study is performed to identify the natural frequencies and vibration modes of the Thomson orange fruit using finite element modal analysis by ANSYS software. In addition, physical properties including mass, volume, density, and principal dimensions were measured, and mechanical properties were determined using Instron Texture Profile Analysis. The dynamic behavior of the orange fruit was simulated using the pendulum impact test. Afterward, the obtained impact was applied to the orange fruit by force gauge and three-axis accelerometer sensors in both polar and equatorial directions. The three-dimensional geometric model of the orange fruit was drawn in the ANSYS software. After meshing and applying the boundary conditions, the first 20 modes and corresponding natural frequencies were obtained. Since the objective of this study was to identify the natural frequencies of the orange fruit, it was considered to have free movement and rotation in space. The results showed that the natural frequencies of orange fruit are in the range of 0 to 248.41 Hz. Knowledge of the texture characteristics and dynamic behavior of horticultural products is essential for the design and development of agricultural machinery. Furthermore, the design and development of agricultural machinery are directly related to the biological properties of agricultural products.Materials and MethodsThe Thomson orange variety was used in the present study. The oranges used for the experiments were harvested from the Citrus and Subtropical Fruits Research Institute in Ramsar, Iran, located at coordinates 50° 40′ E and 36° 52′ N. The oranges were subsequently divided into two groups: large (average diameter 82 mm) and small (average diameter 66 mm). Conducting the finite element analysis requires knowledge of the physical and mechanical properties of the flesh and skin of the orange fruit. The physical and mechanical properties of the tested samples include geometric dimensions, modulus of elasticity, Poisson’s ratio, and density. In the present study, the dynamic behavior of the orange fruit under dynamic loads was investigated by performing an impact test using a pendulum. The orange fruit was hung from the ceiling using a thin thread to perform experimental tests and extract the modal parameters. The orange samples were subjected to impact at three angles: 7° (below the yield point), 10° (at the dynamic yield point), and 20° (above the dynamic yield point).Results and DiscussionThe comparison of the experimental (laboratory) natural frequencies and simulation validates the simulation results. The experimental natural frequencies of the first, second, and third modes in the large-group oranges are 125.4, 146.9, and 180.4 Hz, respectively. Additionally, the simulation (modal) frequencies are 133.80, 146.16, and 196.66 Hz for the first three modes, respectively. The lowest and the highest differences were observed in the second (0.5%) and third (9.01%) modes, respectively. In the small-group oranges, the first, second, and third modes have experimental natural frequencies of 152.2, 188.8, and 242.2 Hz, respectively, and simulation frequencies are 167.79, 187.50, and 248.30 Hz. The second and first modes exhibited the smallest and largest disparities between experimental and simulated natural frequencies, respectively, at 0.68% and 10.24%.ConclusionWhile there are certain limitations, it is undeniable that Computer Aided Engineering (CAE) applications are advantageous for predicting the natural frequencies and vibration modes of spherical fruits such as oranges. Utilizing the obtained frequencies, especially the resonance frequency and the vibrational mode shape, enables us to avoid the resonance frequency in the actual transportation of oranges. This is possible through the implementation of suitable packaging and transportation methods, thereby mitigating the deterioration of fruit quality and ensuring an accurate prediction of its shelf life.
Post-harvest technologies
A. Heydarian; E. Ahmadi; F. Dashti; A. Normohammadi
Abstract
IntroductionThe quick deterioration of fruit and vegetables has led researchers to find a solution to increase the shelf life. Foodstuff packaging is a vital technology to maintain freshness, prevent deterioration, and physiological and mechanical damages, and increase the shelf life of fresh products. ...
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IntroductionThe quick deterioration of fruit and vegetables has led researchers to find a solution to increase the shelf life. Foodstuff packaging is a vital technology to maintain freshness, prevent deterioration, and physiological and mechanical damages, and increase the shelf life of fresh products. Employing various post-harvest technologies prevent light, heat, and humidity transmission and control the microorganism activity, thereby reducing the cost and maintaining the quality of fresh and processed products during storage. Fresh okra has a shelf life of 10 days and is stored at 1-10°C due to high respiration rate and moisture loss. Today, the use of nanotechnology in the packaging industry is developed and expanded. The aim of the packaging is to increase the shelf life and prevent bacterial and shipping damages, as well as control the humidity and gases transmission, thereby reducing food spoilage. Modified atmospheric packaging (MAP) is one of the famous methods for increasing the shelf life of fresh products in which the aging process is reduced by increasing CO2 and decreasing. Decreasing the respiration rate, producing ethylene, and metabolic reactions in the modified atmosphere lead to a reduction in product deterioration. The use of coatings and edible films is being increased in order to maintain sensitive features like flavors, fragrances, and the appearance of different products and increase the shelf time of fruits and vegetables. Chitosan edible coating is a non-fragrance and non-flavor polysaccharide with a high molecular weight that is widely used because of its antifungal, biological, and biochemical properties. Chitosan is a natural polymer obtained from chitin, which is abundantly found in crustacean shells. The aim of the present study is to evaluate the effect of packaging films and chitosan coating under the modified atmosphere storage condition on qualitative and quantitative parameters of okra during storage.Materials and MethodsThe process of present research was performed in the Laboratory of Mechanical Properties and Rheology of the Biosystem Engineering Department, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, in 2016. Okra cv. Kano Dwarf was selected due to its short post-harvest life and provided by farms in Kermanshah Province. Okras were handpicked and they were free of any spots, contamination, or decay, with the almost same size and shape, without any mechanical and microbial damage. The treatments of the present study were chitosan covering, modified atmosphere by a gas mixture of 5% O2 + 10 CO2 + 85% N2, three types of packaging films including silicone nano-emulsion (Nano Bespar Aytak Co.), nano-polyethylene, and light polyethylene (LFO200), as well as two temperature levels of 1 ± 4°C (refrigerator) and 1 ± 25°C (room temperature). The influence of modified atmospheric treatments, chitosan coatings, and packaging films at two storage temperatures on chemical factors (pH and TSS) and mechanical properties including shear stress (TB), shear force (FB), shear modulus (GK) were evaluated at the end of 12 days of storage in a completely randomized design with a factorial experiment in three replications on Okra.Results and DiscussionAmong the films used, silicon nano emulsion film and chitosan coating were more able to maintain TSS. The pH value decreased due to the control of respiratory rate and corruption under modified atmospheric conditions. The mechanical properties of the samples showed that the shear stress changes of the coated sample were significantly less than the untreated ones compared to the beginning of the maintenance period. The sample stored at 4°C had less shear force during the storage period than similar specimens at 25°C. The modified atmosphere caused the shear modulus to decrease with increasing storage time compared to the beginning of the storage period.ConclusionThe results of the present research revealed that silicon nano-emulsion film has a higher capability in preserving the qualitative and quantitative properties of okra compared to other studied films. Between the two studied temperatures, 4°C storage temperature had better performance in preserving qualitative and quantitative properties of the okra compared to 25°C. The controlled atmosphere increases okra's shelf life due to reduced respiration rate. In general, maintenance of the products in a modified atmosphere package preserves the quality of the products and extends their shelf life.
S. Khodamoradi; E. Ahmadi
Abstract
Introduction Grape fruit set its fruits and shortly after planting and due to high nutritious value and excellent food quality has been welcomed by many people in the world, but considering its soft tissue and high softening velocity and sensitivity to fungi attack it is known as an extensively vulnerable ...
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Introduction Grape fruit set its fruits and shortly after planting and due to high nutritious value and excellent food quality has been welcomed by many people in the world, but considering its soft tissue and high softening velocity and sensitivity to fungi attack it is known as an extensively vulnerable fruit. One of the most important ways to maintain fruit quality, decrease vulnerably and assist more appropriate storage, is the use of coating method and proper packing of agricultural products and combining these procedures to decrease damages in storage. Edible coatings provide a replacement and fortification of the natural layers at the product surface to prevent moisture losses, gas aromas, and solute movements out of the food, while selectively allowing for controlled exchange of important gases, such as oxygen, carbon dioxide, and ethylene, which are involved in fruit respiration. Chitosan is the most common polysaccharide-based coatings. Chitosan films have been successfully applied as edible material in films and coatings for the quality preservation of different fruit. In this study, the effects of the application of chitosan edible coatings and storage time on some physical, chemical, mechanical and rheological properties of grape were investigated during storage. Materials and Methods Grape fruits were screened for physical damages, fungal infections, and size homogeneity after harvesting from the farm. Then fruits were divided into without coating and fruits with coating. Fruits being coated, prepared in chitosan emulsion and submerged for two minutes and kept at 20°C for one hour for drying the surface coating via airflow. In order to calculate the weight loss, three containers of each grape fruits (treatment and control) collected and after weighing and averaging weight loss were compared to initial weight during storage expressed as a percent. Color intensities were determined using colorimeter samples. In order to determine soluble solids from each sample, refract meter was used and pH amount of each sample was determined. Mechanical traits and fruit stiffness were measured through penetration test using materials test machine Zowick/ Roell having 500 N loadcell in line with the small diameter with concave probe (5 mm diameter), the penetration depth of 2 mm and loading rate of 10 mm s-1. Mechanical traits including stiffness and elasticity module calculated from the force-deformation curve. Viscoelastic materials have the properties of both viscous and elastic materials and can be modeled by combining elements that represent these characteristics. A viscoelastic model, called the Maxwell model which can predict behavior was evaluated. Results and Discussion In this current study, the application of chitosan coating significantly reduced the fresh grape decay. Fruit decay of grape increased with storage time, but the coating reduced the rate of decay with the length of storage. According to the results, the application of these coatings has a positive impact on yield stress and energy of rupture product texture during the storage. Results of variance analysis showed that temperature, coating and storage time has a significant effect (1% level) on some of the engineering properties of the grape. Storage time has a significant effect on elasticity, while the coating does not have a significant effect on this parameter. Finally, results showed that the application of chitosan coating has an effect on relaxation time and stress. So during storage of coated samples these parameters decreased compared to uncoated. Conclusion Edible films and coatings may reduce the moisture transfer, the rate of oxidation and respiration which are considered important to prolong the shelf-life of these products. This investigation showed that the chitosan coatings are effective for grape shelf life extension and retarded the senescence process compared with control. The coat has been as a physical barrier for the gas exchange between the fruit and the environment. It was demonstrated that the coating reduced the loss of firmness and delayed the softening of fruit and texture change.
S. Youneji; E. Ahmadi; A. Alavi Nia
Abstract
Introduction The mechanical impacts occur mainly during harvesting and post-harvesting operations, lead to the breaking of cell membranes in cellular structure that dependS on impact intensity. Furthermore, turgor pressure of potato tissue is influenced by the micromechanical and the physiological changes ...
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Introduction The mechanical impacts occur mainly during harvesting and post-harvesting operations, lead to the breaking of cell membranes in cellular structure that dependS on impact intensity. Furthermore, turgor pressure of potato tissue is influenced by the micromechanical and the physiological changes in the storage duration. Micromechanical changes of potato tissue due to the mechanical impact need to be monitored by microscopic images during storage. Scanning electron microscopy (SEM) is a high-resolution technique used to investigate the micromechanical behavior of potato tissue. Materials and Methods Potato samples (‘Sante’ cultivar), were stored at 5 ± 0.5°C and 85% relative humidity for 16 weeks. By 2-week intervals, potatoes were removed from the storage and then the impact test was done. Experimental factors were impacted energy at three levels of control (no impact was done), impact energy 1 (0.031 ± 0.002 J) and impact energy 2 (0.320± 0.020 J) and the radius of curvature at two levels of (35 and 45 mm). Water content was measured by drying thin slab samples in an oven at 70°C to a constant weight. The cell turgor pressure of potato tissue at 2-week intervals was estimated from the linear regression between turgor values of each mannitol solution (0–0.6 M) and relative volume change. The microstructural changes of impact location on the potato tubers were analyzed by SEM images at 2-week intervals during storage period. The surface and depth sections cutting from the impact location were immediately immersed in 2.5% glutaraldehyde in 0.1 M sodium phosphate buffer (2 h) at 4± 0.5°C. The specimens were then rinsed 3 × 10 min in 0.1 M sodium phosphate buffer (pH 7.2), and dehydrated through an ethanol series, 25, 50, 70, 90 and 100% dry, 15 min each step, 2 × 100%. In this study the HMDS as a high-quality chemical drying was investigated. The sample preparation for SEM observation then followed by chemical drying via HMDS, under a laboratory hood overnight. Analysis of variance test based on completely randomized design (CRD) was considered for all of the data using SPSS 23. Results and Discussion Superior preservation of potato microstructure was obtained by hexamethyldisilazane (HMDS) drying during sample preparation for SEM observation. The MIP software was used for quantitative analysis of SEM images and the microstructural features of potato tissue at the impact location were determined. So that each cell outline was manually separated by drawing the lines along the visible contours of cell walls. Measurement of the impact damage dimensions was done by MIP software for the surface section (major and minor width, w1 and w2) and the depth section (depth, d and major width, w1). The results indicated the significant differences between water content, cell turgor pressure, cell area and cell perimeter over 16 weeks storage. Generally, by increasing impact intensity the water content, cell turgor pressure, cell area and cell perimeter significantly decreased. Also interaction effect of storage time, impact level and radius of curvature for impact damage of potato tissue was significant. Conclusion The cell turgor pressure at the impact location on the potato tubers had the similar trend with the water content. SEM investigation showed that potato parenchyma, which was high preserved by HMDS drying, had consisted of the pentagon and hexagonal thin-wall cells with the average cell area of 23.14 × 103 ± 0.178 μm2, the average cell perimeter of 564.98 ± 2.008 μm at week 0. The higher impact damage was at week 16 of storage, impact level 2 and the radius of curvature of 35 mm compared to the other treatment.
A. Mansouri Alam; E. Ahmadi
Abstract
Introduction The most important post-harvest mechanical damage is bruising. Bruising occurs during the stages of handling, transporting and packaging due to quasi-static and dynamic loads. Vibrations of tomato fruits during transportation by truck will decrease their quality. More than 2.5 million tons ...
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Introduction The most important post-harvest mechanical damage is bruising. Bruising occurs during the stages of handling, transporting and packaging due to quasi-static and dynamic loads. Vibrations of tomato fruits during transportation by truck will decrease their quality. More than 2.5 million tons damages have been reported during tomato transportation in Iran. Therefore, it is necessary to recognize different parameters of damages during road transportation in order to detect and prevent bruising injury. Materials and Methods In this study, healthy Super Queen verity of tomatoes devoid of any corrosion and mechanical damage multipliers were used. Aaverage of 7 and 5 pieces of fruit in each length and width, respectively in 13*25*37 cm boxes with a capacity of 8 kg were arranged. The boxes were divided into 2 types of truck suspension (model M2631 AIMCO, manufactured in 2010 with air suspension and Nissan trucks 2400, manufactured in 2010 with suspension spring). Boxes were established in three different heights truck, floor truck, height of middle and top of truck, in addition to two different situation boxes on the front axle (S1) and rear axle (S2). In each situation, three levels of height (H1), floor truck, the truck (H2) and the truck (H3) there. The location of each sample inside the fruit boxes bottom row (Loc1) and top (Loc2) boxes marked with marker. In this study, two types of road, highway asphalt and asphalt secondary road was used for transportation. Trucks and vans had the same distance route about 400 km. Fruits were transferred to Hamadan agricultural college. Rheology lab test was a hit with the pendulum. In this study, the amount of energy absorbed from the index (as a parameter to determine the sensitivity) and the fruits bruises were used. Hit test was done after transportation of fruits and transferring those to the laboratory in less than 2 hours. Impact energy products were considered higher than the dynamic submission, dynamic submission to the multiple ways in constant height (CHMI) were determined on the control fruits, impact energy yield limit dynamic range (0.0012) was Jules. Results and Discussion Analysis of variance showed that the main factors including truck, boxes of floor height, box situation on the front and rear axles of the vehicle as well as the location of the fruit (the top and bottom of the box) has a significant effect on energy absorption. There are also some double and triple interactions energy absorbed as a factor of bruising damage in the pendulum test was significant at the 5% possibility level. Means comparison showed that the effect of the truck in height. By increasing the height from the floor of the vehicle, bruising injury increased significantly. The results showed that the fruits which transported with air suspension are healthier than those with truck suspension spring. The maximum amount of absorption energy at third height (H3) spring suspension system (T2) and rear axle (S2) with the amount respectively 491.11 and 488.59 percent increase (compared with control fruit) belong the top row fruits and bottom row fruits inside the box (in secondary asphalt), and maximum resistance bruising in the first height (H1) air suspension system (T1) and front situation (S1) with 180.42 percent increase was observed to control fruits (in highway asphalt). The overall results show that fruit damages are low during transportation with the front axle vehicle. The results also showed that asphalt road highway and truck with air suspension system, Groups of maximum and minimum absorbed energy was more logical than truck suspension spring.
E. Ahmadi; H. Barikloo
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 ...
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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.
Z. Nadim; E. Ahmadi
Abstract
Introduction: The maintenance of the quality of fresh products is still a major challenge for the consumers. The most important quality attributes contributing to the marketability of fresh fruit include appearance, color, texture, flavor, nutritional value and microbial safety. Strawberry fruits should ...
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Introduction: The maintenance of the quality of fresh products is still a major challenge for the consumers. The most important quality attributes contributing to the marketability of fresh fruit include appearance, color, texture, flavor, nutritional value and microbial safety. Strawberry fruits should be firm but not crunchy. Decreased quality during postharvest handling is most often associated with water loss and decay. The postharvest life of strawberries can be extended by coating technique combined with refrigeration. Application of edible coatings is a conventional method to increase shelf life and maintain fruit quality. Edible coatings can provide an alternative to enlarge fresh fruits’ postharvest life. In this study, the effects of application of methyl cellulose edible coatings and storage time on some mechanical properties, including: the yield stress, yield strain, energy of rupture and modulus of elasticity and also, the viscoelastic behavior of the strawberry fruit was investigated.
Materials and Methods: MC (Methocel, Dow Chemical Company, Midland, MI) coating was prepared by solubilizing MC powder (3.0 g per 100 mL) in a water–ethyl alcohol mixture (2:1) at 75ºC under the high speedmixer (900 rpm) for 15 min. Coatings were used directly on the fruit surface. The physical and mechanical characteristics of fruits were analyzed on 2, 5, 8 and 11 days of storage. The puncture test and relaxation test were done using a texture analyzer (Zwick/Roell Model BT1_FR0.5TH.D14, Zwick GmbH Co., Ulm, Germany; using Xforce HP model of loadcell with capacity of 500 N, by 2 mv/v characteristic). General Maxwell model is widely used to analyze experimental results of the stress tests applied for relaxation. The obtained model coefficients were determined and evaluated from relaxation stress curves. Residues were determined using the sequential model. Usually, multicomponent models can properly describe the actual behavior of agricultural products. Results of factorial experiment in a completely randomized design were analyzed. In this study, the stress versus time graph was plotted and three-component Maxwell model coefficients were obtained.
Results and Discussion: In this current study, application of MC significantly reduced the fresh strawberries decay. Fruit decay in strawberries increased with storage time, but the coating reduced rate of decay with the length of storage. According to the results, the application of these coatings has a positive impact on yield stress and energy of rupture product texture during the storage. Average yield stress and rupture energy for the coated samples and control were 0.11, 5.71 and 0.09, 4.12 MPa respectively. The effect of treatment and storage time on the yield strain and elastic modulus were not statistically significant. The results show that provided Maxwell model satisfactorily (RMSE0.96) fits the experimental data. Also, with a retention time, the elastic component of the model is relatively reduced and the application of the coating prevents the decrease in relaxation time and improves the rheological properties of fruit. Relaxation time is different based on the characteristics of the viscoelastic or viscous substances, but this time is wider in elastic material. The relaxation time depends on the moisture content of the product, so the increase of humidity and soft, reduced relaxation time. Coatings are effective physical barrier to moisture loss and slower rates of weight loss in coated fruits because of the cover features for gas diffusion of stomata, the organelles that regulate the transpiration process and gas exchange between the fruit and the surroundings.
Conclusions: Edible films and coatings may reduce the moisture transfer, the rate of oxidation and respiration which are considered important to prolong the shelf-life of these products. This investigation showed that the MC coatings are effective for strawberries shelf life extension and retarded the senescence process in compared with control. The coat has been as a physical barrier for the gas exchange between the fruit and the environment. It was demonstrated that the coating reduced loss of firmness and delayed the softening of fruit and texture change. Fruit decay in strawberries increased with storage time, but the coating reduced rate of decay with the length of storage. Finally the results showed that coating, may increase overall acceptability, and increase the quality and shelf life of fruits.
