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Article

Effects of Packaging Constraints on Vibration Damage of ‘Huangguan’ Pear During Simulated Transport

by
Lijun Wang
1,2,*,
Zechen Xie
1,
Yumeng Wu
1,
Jinguo Gao
1 and
Haiyan Song
1,2,*
1
College of Light Industry Science and Engineering, Tianjin University of Science and Technology, Tianjin 300457, China
2
State Key Laboratory of Bio-Based Fiber Materials, Tianjin 300457, China
*
Authors to whom correspondence should be addressed.
Horticulturae 2025, 11(7), 749; https://doi.org/10.3390/horticulturae11070749
Submission received: 19 May 2025 / Revised: 16 June 2025 / Accepted: 25 June 2025 / Published: 1 July 2025
(This article belongs to the Special Issue Postharvest Treatments and Storage Technologies Applied to Ensure the Quality and Shelf-Life of Fruits and Vegetables)
Browse Figures
Versions Notes

Abstract

Fruit is typically transported in stacked packaging units, where external packaging constraints play a critical role in influencing mechanical damage during transit. This study primarily investigated the effects of external packaging constraints on vibration-induced damage and response vibration in ‘Huangguan’ pears (Pyrus bretschneideri Rehd. ‘Huangguan’). Three external packaging constraint types—free constraint, elastic constraint, and fixed constraint—were applied to a two-layer stacked packaging system to limit vertical movement. The pears inside the containers were divided by a corrugated paperboard. Vibration excitation was simulated using the ASTM D4169 spectrum at three vibration levels. Damage indicators, including damage area, flesh firmness, respiratory rate, weight loss, titratable acidity, ascorbic acid, and tissue microstructure, were analyzed after vibration experiments. The results demonstrated that external packaging constraint type significantly affects the mechanical damage of ‘Huangguan’ pears, with damage severity being closely related to constraint strength. Comprehensive analysis revealed that the most severe damage occurred under free constraint, while the least damage was observed under fixed constraint. Stacking position also influenced damage, as pears on the top layer exhibited more severe damage compared to those on the bottom layer. The response vibration results aligned with the observed damage patterns. SEM analysis further revealed that vibration disrupted the tissue microstructure and damaged stone cells, which decreased in number and even disappeared at higher vibration levels. This study provides valuable insights for improving postharvest transport packaging designs and minimizing fruit loss during logistics.

1. Introduction

Modern logistics enable the transportation of fruit across long distances. However, during transportation, fruit is inevitably exposed to hazards such as compression, impacts, and vibrations, often caused by poor road conditions, leading to mechanical damage [1]. This damage results in various issues, including tissue softening, browning, changes in respiratory rate, enzyme activity, and even fruit rot [2], which alter the physiological and mechanical properties of fruit. Mechanical damage also has an influence on the shelf life of fruit. In China, postharvest fruit losses are estimated at 20–30%, representing a significant waste of resources.
Static compression, impact, and vibration are the primary factors contributing to the mechanical damage of fruit during logistics. Fruit packages are often placed in stacked forms to facilitate handling and transportation. Static compression can lead to fruit damage due to the improper design of packaging and stacking arrangements [3,4]. The extent of damage caused by static compression depends on factors such as compression direction and velocity. Impact damage during loading, handling, and sorting processes is a common issue in logistics. Dynamic pressure has been found to cause more severe mechanical damage to fruit compared to static pressure [5,6].
An et al. [7,8] highlighted that the initial collision velocity significantly affects the degree of damage to strawberries. Key factors such as drop height, impact speed, and impact load play crucial roles in determining the extent of mechanical damage to fruit [9,10,11]. Studies have also investigated the bruise susceptibility of apples, pears, and blueberries under impact [12,13,14]. Additionally, environmental conditions such as temperature and humidity influence the mechanical damage sustained by fruit during logistics [15,16,17].
Vibration is a critical factor contributing to the mechanical damage of fruits after harvest [18]. It accelerates the quality deterioration of fruits. Studies on kiwifruit [19] and wax apples [20] have demonstrated that vibration leads to a decline in firmness and an increase in weight loss and respiratory rate. Vibration also impacts ethylene release, enzymatic activity, fruit browning, titratable acidity (TA), total soluble solid content, and even gene expression [21,22]. The excitation vibration experienced by packaged fruit during transportation is random. The extent of mechanical damage to fruit during transportation is determined by the response vibration, which is influenced by the vibration mode and the excitation vibration. Variations in packaging height and stacking positions can result in different levels of fruit damage [23]. Key factors such as vibration frequency [24], vibration level [25], and vibration duration [26] significantly impact the mechanical damage to fruit. The severity of vibration damage increases with higher vibration levels and prolonged durations. Wang et al. [27] revealed that vibration damage to ‘Huangguan’ pears was significantly influenced by the excitation acceleration spectrum shape, with the mechanical damage primarily attributed to the acceleration PSD amplitude in the resonant region. The constraints imposed by packaging, such as binding and wrapping, also affect the vibration modes of stacked units. Variations in external packaging constraints lead to different response vibrations, which in turn influence the mechanical damage to fruit. However, only a few studies have explored the effects of these external packaging constraints on the mechanical damage of fruit.
Currently, various packaging methods are utilized for fruits, which represent a significant factor influencing damage during transportation [28,29]. Commonly used materials, such as expanded polystyrene (EPS), expanded polyethylene (EPE), corrugated paperboard boxes (CFBs), and polyurethane (PU), are widely used in fruit packaging due to their excellent mechanical properties. Studies on cushioning materials for ripe peaches have demonstrated that PU and CFB outperform EPE + CFB and CFB alone in mitigating vibration damage [30]. Similarly, the protective effects of different packaging types on wax apples have been extensively studied [20]. Research further indicates that EPS trays and EPE nets provide exceptional cushioning performance for ‘Huangguan’ pears [31]. However, materials such as EPS and EPE are non-degradable and pose significant environmental concerns. Consequently, the development of eco-friendly packaging materials has become a critical focus for the future of fruit packaging. Recent studies have investigated the cushioning performance of eco-friendly foam for guava under impact conditions, showcasing its potential as a sustainable alternative [32].
The ‘Huangguan’ pear (Pyrus bretschneideri Rehd. ‘Huangguan’) is very popular in China [33]. Its high juice content and thin peel make it particularly susceptible to mechanical damage during postharvest transportation. This study aims to address this issue with the following objectives: (1) to investigate the effects of external packaging constraints on the mechanical damage of ‘Huangguan’ pears; (2) to evaluate the mechanical damage sustained by the pears under varying vibration levels; and (3) to analyze the changes in the physiological properties, mechanical performance, and tissue microstructure of the pears following exposure to vibration.

2. Materials and Methods

2.1. Material Sample Preparation

In this experiment, ‘Huangguan’ pears at the same stage of maturity were harvested from Zhaoxian County, Shijiazhuang City, Hebei Province. Pear samples with uniform size and color, free from any mechanical damage, were selected for this study. After harvesting, the pears were immediately transported to a laboratory in Tianjin City. The quality of the initial pear samples was evaluated by measuring the parameters of 12 randomly selected pears. The firmness of three positions on the equator of each pear was measured, and the average firmness of the three positions was used as the firmness of each pear sample. The initial firmness of the pear samples was calculated by taking the average firmness of the 12 pear samples. The average diameter and weight of the pears were 0.084 m and 0.339 kg, respectively, while the average firmness was 57.59 N.
To simulate a stacked unit during logistics, a two-layer stacked packaging design for ‘Huangguan’ pears was developed, as shown in Figure 1. Each corrugated paperboard box, measuring 0.30 m × 0.30 m, contained nine pear samples separated by a corrugated paperboard divider with a UV flute. The divider had a thickness of 0.005 m. An electronic dynamic shaker (model DG-600-6, Sushi Testing Instrument Co., Ltd., Suzhou, China) with a frequency range of 3–5000 Hz and a maximum load capacity of 200 kg was used in this study. The stacked packaging system was secured on the shaker table under different constraints to investigate the effects of external packaging constraints on the mechanical damage of ‘Huangguan’ pears. The constraints can limit the vertical movement of the stacked packaging system. Three constraint conditions were tested to simulate the different external packaging constraint conditions: (1) free constraint where the stacked packaging system could move freely in the vertical direction; (2) elastic constraint where the stacked packaging system was constrained by an elastic strap with a constraint force of 25.30 N; and (3) fixed constraint where the motion of the stacked packaging system was nearly restricted by the constraints. The packaging system was restricted by a rigid frame.

2.2. Experiment Scheme

Simulated truck random vibration experiments were conducted to investigate the effects of packaging constraints on the mechanical damage of ‘Huangguan’ pears. The ASTM D4169 [34] truck spectrum, with three vibration levels of 0.70 g, 0.54 g, and 0.40 g (Figure 2), was used as the excitation acceleration power spectral density (PSD). ASTM D4149 truck spectrums were used to simulate truck vibration during transportation. The spectrums and vibration levels were designed based on the measurement and survey of the real truck vehicle vibration of a large number of distribution routes. The three vibration levels of 0.70 g, 0.54 g, and 0.40 g represented the high, medium, and low vibration intensity seen in real truck transportation. Each vibration test was conducted for 3 h, and the response acceleration signal of pears located at the corner positions was recorded. Each experiment under different conditions was repeated twice to ensure accuracy and repeatability. The experimental design is summarized in Table 1. All vibration tests were conducted under controlled environmental conditions of 23 °C and 50% relative humidity (RH).

2.3. Measurement of Mechanical Damage of Pear Sample

The quality changes in the pear samples were evaluated based on their mechanical properties and physiological performance following the vibration experiments. To better observe the damage zones, pear damage was assessed 24 h after the vibration experiments. In this study, the quality of the pears was assessed through appearance (damage area), mechanical properties (firmness), and physiological performance (respiratory rate, weight loss, titratable acidity (TA), and ascorbic acid content). All samples were evaluated for damage area and weight loss, while three pears from each box were selected to measure flesh firmness, respiratory rate, TA, and ascorbic acid content. Therefore, the sample size of the damage area and weight loss was 36, while the sample size for flesh firmness, respiratory rate, TA, and ascorbic acid content was 12.

2.3.1. Damage Area

Three-dimensional scanning technology was employed to accurately measure the damaged area of ‘Huangguan’ pear fruit following vibration tests. A handheld 3D scanner (FreeScan EP, Shining 3D Co., Ltd., Hangzhou, China) was used for this purpose. Initially, the pear samples were scanned after the vibration tests. Subsequently, Geomagic Wrap (2021) and SolidWorks software (2021) were utilized to extract and calculate the damaged areas of the pear samples through the normal vectoring detection method. The shooting distance was 5–15 cm, under which clear and high-precision pear outlines can be obtained. The wavelength was 405 nm for scanning. Figure 3 shows the measurement process of the damage area by taking a pear sample with obvious damage as an example.

2.3.2. Flesh Firmness

A texture analyzer (TA.XT Plus, Stable Micro Systems, Co., Golalming, UK) was utilized to measure the flesh firmness of ‘Huangguan’ pears. The pericarp of each pear was carefully peeled before measurement. The P 2 probe was selected for the assessment of flesh firmness, which was measured at the 3 equatorial positions of the fruit. The probe puncture depth was 1 cm. The average value of the firmness of the 3 positions was calculated to ensure accuracy.

2.3.3. Respiratory Rate

The PBI Dansensor (CheckMate 9900, Ringsted, Denmark) was employed to measure the respiration rate of the pear fruit. Pear samples were placed in polyethylene terephthalate (PET) containers sealed with plastic wrap. The containers were then stored in a chamber maintained at 23 °C and 50% RH for 24 h. Following incubation, the concentrations of C O 2 were measured using the PBI Dansensor. Each measurement was performed three times per pear sample, and the average value was recorded as the final result. The respiration rate was calculated using Equation (1).
R e s p i r a t o r y   r a t e = 19.64 × C C O 2 × ( V 1 − V 2 ) / ( t × m )
where C C O 2 represents the concentration of C O 2 ; V 1 and V 2 are the volume of the PET container and the pear sample, respectively; t is the measurement time; m is the original mass of the pear sample.

2.3.4. Weight Loss

Before the vibration experiment, an electronic balance (STP-2000, Mettler Toledo Co., Shanghai, China.) was used to measure the initial weight of the pear samples. After the vibration experiment, the pear samples were placed in a chamber maintained at 23 °C and 50% RH for 24 h. Following this period, the pear samples were weighed again.
The weight loss rate of the pear samples was calculated using Equation (2).
W e i g h t   l o s s   r a t e = W 1 − W 2 W 1 × 100 %
where W 1 is the weight before the vibration experiments, and W 2 is the weight 24 h after the vibration experiments.

2.3.5. TA and Ascorbic Acid

The pear samples were chopped into small pieces and squeezed to extract juice to measure TA and ascorbic acid content. The acid–base titration method was used to determine the TA content. A 20 mL portion of juice was extracted from each fruit and titrated with a 0.1 mol L−1 NaOH solution until the pH reached 8.1, which was considered the endpoint. Each pear sample was measured three times, and the average value was recorded. The measurement of ascorbic acid content followed the method described by Octavia [35].

2.3.6. Microstructure Observation

The microstructures of the pear flesh were analyzed using an optical microscope (Nikon ECLIPSE LV100ND, Tokyo, Japan) and a scanning electron microscope (SEM) (JSM-IT300LV, JEOL Ltd., Tokyou, Japan). For pear samples without visible bruises, flesh samples were collected from the equatorial regions of the pear, while for damaged pears, samples were taken from the bruised areas. The flesh was carefully cut into slices measuring 1   m m × 5   m m × 5   m m . The microstructure was observed under the optical microscope at 40× and 100× magnifications. At 40× magnification, cell clusters composed of multiple pear pulp stone cells were visible, while at 100× magnification, individual pear pulp stone cells could be observed. For SEM observation, the pear flesh samples were pretreated through freezing and drying. The microstructure was analyzed by SEM at 80× magnification.

2.3.7. Statistics Analysis

An analysis of variance was conducted to evaluate the effects of the main treatments (vibration level and constraint type) and their interactions on the quality changes in ‘Huangguan’ pears. All statistical analyses and correlations between pear quality measurements were performed using Origin software. (2022) Differences were considered statistically significant when p < 0.05.

3. Results and Discussion

3.1. Analyzing the Response Vibration of the Pear Samples

Acceleration power spectral density (PSD) is commonly used to describe random vibration events in the frequency domain, providing a representation of vibration energy distribution across different frequencies. The average vibration level of random vibration ( G r m s ) is expressed as the root mean square (RMS) of acceleration.
G r m s = ∫ S ( f ) d f
where f is vibration frequency, and S f is the one-side acceleration PSD.
The response vibration acceleration PSDs of the pear samples at the corner position under different constraint types are presented in Figure 4. This figure shows that the response acceleration PSD amplitude of the pear samples on the top layer was significantly higher than that of the bottom-layer pears, indicating that the vibration energy transmitted to the top-layer pears was greater.
By comparing Figure 4A–C, it is evident that the external packaging constraint type has a substantial impact on the response acceleration PSD. The PSD amplitude followed the following order: free constraint > elastic constraint > fixed constraint. Additionally, the pears on the top layer were primarily influenced by the first resonant frequency, while the pears on the bottom layer were dominated by the second resonant frequency.

3.2. Analyzing the Microstructure of the Pear Flesh Tissue After Vibration

SEM images of pear tissue microstructures are presented in Figure 5A. Significant differences were observed between the microstructures of intact and damaged pear tissues. In pears that were not subjected to vibration, the cell walls remained intact, and the cells exhibited a dense and regular arrangement. However, after the vibration experiments, the pulp tissue was visibly damaged. The cell walls were destroyed and collapsed, leading to the formation of large gaps. The cell arrangement became irregular, and the cell outlines were indistinct.
As the extent of damage increased, the cell structures further deteriorated, with the cell walls collapsing completely, resulting in the loss of cytoplasm and the appearance of fibrous tissue. These findings indicate that vibration disrupts the regular cellular structure of ‘Huangguan’ pear flesh tissue, making the fruit more susceptible to water loss and microbial contamination.
The microstructure of pear pulp observed through an optical microscope is presented in Figure 5B. Stone cells, a unique structural feature of pear fruit, are one of the key factors influencing its quality. Intact stone cells are visible in the undamaged pear pulp. However, the pear pulp is highly susceptible to vibration, and stone cells were damaged when vibration-induced injuries occurred in the pulp. As the vibration level increased, the damage to the pear pulp became more severe, with fewer intact stone cells visible.
Moreover, the collapse of cell walls led to the exposure of cytosol to the air, resulting in browning. This browning phenomenon is evident in the damaged pears, where the pulp displays significant discoloration. The extent of browning increased with higher vibration levels, further illustrating the impact of vibration on pear pulp quality.

3.3. Analysis of Changes in Pear Quality Indicators

3.3.1. Weight Loss

Figure 6A,B illustrate the weight loss of pear samples 24 h after the vibration experiments. Compared to the control experiments ( G r m s = 0 ), vibration significantly accelerated the weight loss of the pear samples. The weight loss in the control group (without vibration) was 0.39%, while the highest weight loss of 0.76% was observed in samples subjected to 0.70 g vibration under free constraint conditions.
Both external packaging constraint type and vibration level had a certain effect on pear weight loss. As the constraint strength decreased, weight loss increased. For instance, at a vibration level of 0.54 g, the weight loss under free constraint, elastic constraint, and fixed constraint conditions was 0.76%, 0.68%, and 0.57%, respectively. Additionally, pear weight loss was strongly influenced by vibration intensity. Under fixed constraint conditions, the weight loss at vibration intensities of 0.40 g, 0.54 g, and 0.70 g was 0.51%, 0.57%, and 0.64%, respectively.
Figure 6B illustrates that the stacked layer influenced pear weight loss. Overall, pear samples on the top layer exhibited greater weight loss compared to those on the bottom layer. This difference in weight loss was attributed to the vibration response of the pear samples. The response vibration of the pears on the top layer was markedly higher than that of the bottom-layer samples (Figure 4), leading to differences in the extent of damage.

3.3.2. Firmness

Figure 6C,D illustrate the changes in pear firmness following the vibration experiments. The firmness of the pear samples subjected to vibration decreased compared to the control group, indicating that vibration accelerated the decline in firmness. Furthermore, a decreasing trend in firmness was observed as the vibration level increased. Under fixed constraint conditions, the pear firmness at vibration levels of 0.40 g, 0.54 g, and 0.70 g was 54.51 N, 51.02 N, and 47.85 N, respectively.
Figure 6C shows that the external packaging constraint type also had a slight effect on firmness changes. Pear samples under fixed constraint conditions exhibited the highest firmness values, suggesting that the pear samples showed the minimum damage under this constraint type.

3.3.3. Damaged Area

Figure 6E illustrates the damaged area of pears under different vibration levels and external packaging constraint conditions. The results indicate that pear samples under fixed constraint conditions exhibited the smallest damaged area at each vibration level, while free constraint resulted in the largest damaged area. At a vibration level of 0.54 g, the damaged area increased by 103.34% and 141.18% under elastic and free constraints, respectively, compared to the fixed constraint condition.
A positive correlation was observed between the damaged area and vibration level. Both vibration level and constraint type significantly influenced the extent of the damaged area. For instance, under elastic constraint conditions, the damaged area at vibration levels of 0.54 g and 0.70 g was 5.45 and 8.03 times greater than that at 0.40 g, respectively. Additionally, a substantial difference in damaged area was observed between the top and bottom layers of the stacked pears. Pear samples on the top layer had a larger damaged area than those on the bottom layer. At a vibration level of 0.70 g under elastic constraint conditions, the damaged area of pears on the top layer was 50.43% greater than that on the bottom layer. This difference became increasingly pronounced as the vibration level increased.

3.3.4. Respiratory Rate

The respiratory rates of ‘Huangguan’ pears were measured 24 h after the vibration experiments, and the results are presented in Figure 7A,B. Compared to the control group, the respiratory rate of pears increased significantly following the vibration experiments. The highest respiratory rate was observed under 0.70 g vibration with free constraint, while the lowest was recorded under 0.40 g vibration with fixed constraint. At a vibration level of 0.70 g, the respiratory rates under free constraint and elastic constraint were 26.96% and 13.58% higher, respectively, than those under fixed constraint. Additionally, the respiratory rate increased with both vibration intensity and reduced constraint strength. Under elastic constraint, the respiratory rates at vibration levels of 0.40 g, 0.54 g, and 0.70 g were 13.34%, 38.73%, and 49.89% higher, respectively, than those in the control experiment. These results were consistent with the trends observed for weight loss, firmness, and damaged area, suggesting that damage accelerates the respiration process of pears, potentially shortening their shelf life. Moreover, the stacked layer also influenced the respiration rate of the pears. As shown in Figure 7B, pears on the top layer exhibited higher respiratory rates compared to those on the bottom layer.

3.3.5. TA

The changes in the TA content of ‘Huangguan’ pears under random vibration are presented in Figure 7C,D. TA serves as an indicator of the acid substance content in pears. The vibration level significantly influenced the TA content of the pear samples, showing a clear declining trend as the vibration level increased. This suggests that more severe damage results in lower TA content. The TA content followed the order free constraint < elastic constraint < fixed constraint and decreased in the sequence of 0.40 g > 0.54 g > 0.70 g. Additionally, the TA content of pears on the top layer was slightly lower than that of pears on the bottom layer.

3.3.6. Ascorbic Acid

When the cells of fruit are damaged, enzymes interact with substances such as ascorbic acid, initiating oxidation reactions. Additionally, ascorbic acid undergoes consumption due to the metabolic activity of damaged cells. As a result, more severe damage generally leads to lower ascorbic acid content. Figure 7E,F illustrate the changes in ascorbic acid content in pear samples following the vibration experiments. The highest ascorbic acid content (0.04 g kg−1) was recorded under a vibration level of 0.40 g with fixed constraint, while the lowest content (0.02 g kg−1) was observed under 0.70 g vibration with free constraint. Figure 7F reveals that pears in the top layer had lower ascorbic acid content compared to those in the bottom layer.

3.4. Discussion

Previous research has primarily focused on the effects of vibration level, duration, and frequency on the mechanical damage to fruit. Additionally, factors such as vehicle type, environmental conditions, and positional placement have been considered. However, the role of external packaging constraints—a critical factor influencing mechanical damage during transit vibration—has often been overlooked. This paper explores the impact of external packaging constraints on the vibrational response and mechanical damage of ‘Huangguan’ pears.
The mechanical damage of pears was characterized by analyzing the damage area, flesh firmness, respiratory rate, weight loss, TA, ascorbic acid content, and microstructure of flesh tissue. SEM analysis revealed that the microstructure of pear tissue subjected to vibration damage was significantly disrupted. The unique stone cells of pears were destroyed after the vibration experiments. The results from the damage area analysis indicated that the largest damaged area occurred under free constraint conditions, while the smallest was observed under fixed constraint conditions (Figure 6E). Vibration caused a decline in the flesh firmness of ‘Huangguan’ pears (Figure 6C), consistent with the findings from previous studies on ‘Huangguan’ pears [27,31]. The degree of decline in flesh firmness varied across different constraint conditions. Cellular destruction also contributed to weight loss, a conclusion supported by prior research on other fruits [36,37]. The extent of weight loss was closely linked to the type of constraint. Pear damage also led to a loss of nutritional mass, including sugars, organic acids, and minerals. TA and ascorbic acid, key indicators for assessing flavor and nutrition, were significantly influenced by constraint type. Additionally, the results demonstrated that vibration accelerated the respiration rate of the pear samples, with distinct respiratory rates observed under the three constraint conditions.
A combined analysis of the quality indicators of ‘Huangguan’ pears, including damage area, flesh firmness, respiratory rate, weight loss, TA, and ascorbic acid content, demonstrated that vibration accelerates textural deterioration. Proper packaging design is essential for minimizing mechanical damage during transit. Studies have shown that cushioning materials, packaging type, and external packaging play significant roles in enhancing anti-vibration performance. Packaged goods are typically transported in stacked forms, with the stacked units secured using constraints such as elastic ropes, wrap film, or straps. This study revealed that constraints play a critical role in mitigating vibration damage to ‘Huangguan’ pears. The effects of three different external packaging constraints on vibration damage were examined in this paper. The findings underscore the importance of constraint design in minimizing postharvest fruit losses during logistics. Additionally, stack position significantly influenced the extent of mechanical damage, with pears on the top layer experiencing more severe damage compared to those on the bottom layer. These results suggest that cushioning can be enhanced for delicate fruit positioned on the upper layers of stacked units. Higher vibration levels were associated with more severe mechanical damage to pears. Previous studies have demonstrated that spectrum shape has a significant impact on the mechanical damage of ‘Huangguan’ pears. Therefore, selecting the appropriate excitation spectrum is crucial for scientifically evaluating fruit packaging performance in laboratory-simulated tests. The mechanical damage observed in pears was strongly correlated with their response to vibration. The consistency between the response vibration results and mechanical damage data reinforces the validity of using response vibration as an indicator for assessing mechanical damage. Three external packaging constraint cases were discussed in this paper. However, more constraint types deserve to be considered to reveal the correlation between the external packaging constraint and mechanical damage of fruit in future studies.

4. Conclusions

This study primarily investigated the mechanical damage of ‘Huangguan’ pears under different external packaging constraint types. The effects of external packaging constraints on vibration-induced damage were systematically assessed. The results demonstrated that vibration control obviously accelerated the textural deterioration of the pears. Vibration led to a decline in flesh firmness, TA, and ascorbic acid content. Conversely, weight loss and respiratory rate increased following vibration exposure. The microstructure of pear flesh tissue was severely disrupted under vibration, with notable damage to the cell walls. Stone cells were destroyed and, at higher vibration levels, even disappeared entirely, accompanied by the appearance of browning. A positive correlation was observed between mechanical damage and vibration level. Additionally, the stacked position influenced the extent of vibration damage, with pears positioned on the top layer exhibiting more severe damage compared to those on the bottom layer.
The findings revealed that external packaging constraint type has a significant impact on the mechanical damage of pears under random vibration. Pear samples subjected to the three different constraints exhibited varying levels of damage. The severity of mechanical damage followed the following order: free constraint > elastic constraint > fixed constraint. The response vibration of pears was closely related to the strength of the constraints, with mechanical damage largely determined by the response vibration.
This study provided insights into the mechanical damage mechanisms of pears from the perspectives of external packaging constraint, vibration level, and stack position. These findings are valuable for evaluating vibration-induced damage and developing strategies to reduce mechanical damage in transportation.

Author Contributions

Conceptualization, H.S.; methodology, L.W. and H.S.; investigation, Z.X., Y.W. and J.G. data curation, Z.X.; writing—original draft preparation, Z.X.; writing—reviewing and editing, L.W.; visualization, Z.X., Y.W. and J.G.; projection administration, L.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (Grant number 32202116) and Scientific Research Program of Tianjin education commission (Grant number 2019KJ210).

Data Availability Statement

The data underlying this article cannot be shared publicly due to the requirements of the supporting project. The data will be shared upon reasonable request to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The two-layer stacked ‘Huangguan’ pear packaging system with three types of external constraints. (A) Inner pear samples; (B) free constraint; (C) elastic constraint; (D) fixed constraint.
Figure 1. The two-layer stacked ‘Huangguan’ pear packaging system with three types of external constraints. (A) Inner pear samples; (B) free constraint; (C) elastic constraint; (D) fixed constraint.
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Figure 2. ASTM D4169 truck spectrum.
Figure 2. ASTM D4169 truck spectrum.
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Figure 3. Measurement process of damage area using 3D scanning.
Figure 3. Measurement process of damage area using 3D scanning.
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Figure 4. Response power spectral density (PSD) of corner pear samples with different constraints in linear coordinates. (A) Free constraint; (B) elastic constraint; (C) fixed constraint.
Figure 4. Response power spectral density (PSD) of corner pear samples with different constraints in linear coordinates. (A) Free constraint; (B) elastic constraint; (C) fixed constraint.
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Figure 5. The microstructure of the pear flesh. (A) Scanning electron microscope (SEM) images. (B) Microstructure images from the optical microscope.
Figure 5. The microstructure of the pear flesh. (A) Scanning electron microscope (SEM) images. (B) Microstructure images from the optical microscope.
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Figure 6. (A) Average weight loss. (B) Weight loss under different stacked layers. (C) Average firmness. (D) Firmness under different stacked layers. (E) Damaged area. G r m s is root mean square of acceleration. Error bars represent standard deviation. Difference between mean values indicated by different lowercase letters is statistically significant (p ≤ 0.05).
Figure 6. (A) Average weight loss. (B) Weight loss under different stacked layers. (C) Average firmness. (D) Firmness under different stacked layers. (E) Damaged area. G r m s is root mean square of acceleration. Error bars represent standard deviation. Difference between mean values indicated by different lowercase letters is statistically significant (p ≤ 0.05).
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Figure 7. (A) Average respiratory rate. (B) Respiratory rate under different stacked layers. (C) Average TA content. (D) TA content under different stacked layers. (E) Average ascorbic acid content. (F) Ascorbic acid content under different stacked layers. G r m s is root mean square of acceleration. Error bars represent standard deviation. Difference between mean values indicated by different lowercase letters is statistically significant (p ≤ 0.05).
Figure 7. (A) Average respiratory rate. (B) Respiratory rate under different stacked layers. (C) Average TA content. (D) TA content under different stacked layers. (E) Average ascorbic acid content. (F) Ascorbic acid content under different stacked layers. G r m s is root mean square of acceleration. Error bars represent standard deviation. Difference between mean values indicated by different lowercase letters is statistically significant (p ≤ 0.05).
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Table 1. Experiment design.
Table 1. Experiment design.
Free ConstraintElastic ConstraintFixed ConstraintControl Experiment
Vibration level (g)0.70, 0.54, 0.400.70, 0.54, 0.400.70, 0.54, 0.400
Duration (h)3330
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MDPI and ACS Style

Wang, L.; Xie, Z.; Wu, Y.; Gao, J.; Song, H. Effects of Packaging Constraints on Vibration Damage of ‘Huangguan’ Pear During Simulated Transport. Horticulturae 2025, 11, 749. https://doi.org/10.3390/horticulturae11070749

AMA Style

Wang L, Xie Z, Wu Y, Gao J, Song H. Effects of Packaging Constraints on Vibration Damage of ‘Huangguan’ Pear During Simulated Transport. Horticulturae. 2025; 11(7):749. https://doi.org/10.3390/horticulturae11070749

Chicago/Turabian Style

Wang, Lijun, Zechen Xie, Yumeng Wu, Jinguo Gao, and Haiyan Song. 2025. "Effects of Packaging Constraints on Vibration Damage of ‘Huangguan’ Pear During Simulated Transport" Horticulturae 11, no. 7: 749. https://doi.org/10.3390/horticulturae11070749

APA Style

Wang, L., Xie, Z., Wu, Y., Gao, J., & Song, H. (2025). Effects of Packaging Constraints on Vibration Damage of ‘Huangguan’ Pear During Simulated Transport. Horticulturae, 11(7), 749. https://doi.org/10.3390/horticulturae11070749

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