Document Type : Research Paper
Apple (Malus myrus) is one of the oldest fruits known to humankind, with its origin, according to some theories, tracing back to the Caucasus region, the Caspian Sea, and the Mediterranean. This fruit, belonging to the Rosaceae family, has been cultivated in regions such as Iran, Egypt, Rome, and Greece. Key apple cultivars in Iran include Golden Delicious, Red Delicious, Golab, Fuji, Gala, Granny Smith, and Abbas Shahi Mashhad. Statistics from 2003 indicate that the cultivation area for apples in Iran was approximately 152,000 hectares.
One of the major challenges in Iran’s agricultural sector is the high rate of post-harvest losses, which reaches up to 30% in Iran, compared to the global average of 2%. Despite traditional systems still being used for planting, maintenance, and harvesting, the highest losses occur during post-harvest stages.
Various factors contribute to increased spoilage, including mechanical damage from impact during harvesting or transportation, environmental damage such as hail and wind, and harvesting at an inappropriate time. Main strategies for reducing losses include using high-quality cultivars, proper orchard management, training on correct harvesting techniques, reforming the post-harvest process structure, and increasing the number of cold storage facilities. Determining the optimal harvest time, measured by criteria such as the sugar-to-acid ratio and tissue firmness, plays a vital role in shelf life. Early harvesting reduces quality, while late harvesting shortens the storage duration. Unfortunately, in Iran, less attention is paid to harvest time standards.
To combat rapid spoilage, modern processing methods such as irradiation (the use of ionizing radiation) have been considered. This process (also known as “cold pasteurization”) sterilizes the fruit by eliminating microorganisms without causing noticeable changes in the fruit’s texture or sensory characteristics. Numerous studies on Ultraviolet (UV) radiation have shown that treating fruits (such as peaches and tomatoes) with these rays, especially at low doses, delays the ripening rate and reduces storage rots. However, long-term treatment with UV-C can lead to the oxidation of the fruit’s natural wax and, if the epidermal cells are damaged, the loss of the wax’s regenerative capacity. Furthermore, at high doses, it may cause skin burn and a reduction in beneficial compounds like anthocyanins.
The primary objective of the research mentioned previously is to investigate the effects of Ultraviolet radiation exposure on the mechanical properties and shelf life of the Golden Delicious apple cultivar, which are subject to post-harvest bruising. This investigation also includes the use of an ultrasonic measurement method to evaluate changes in the mechanical properties of the fruit tissue
The present research was conducted to investigate the effects of Ultraviolet (UV-C) irradiation on the mechanical properties and storage life of export-quality Golden Delicious apples. The apples were harvested manually from orchards in Najafabad, Isfahan (year 1401 [2022/2023]), 170 days after flowering, in early Mehr (late September/early October), to ensure freshness and freedom from mechanical damage. To prevent damage during transfer to the laboratory, export cardboard boxes with shock-absorbing straw padding were used, as apples are most vulnerable to mechanical damage in the first few days post-harvest. Upon arrival, apples with visible defects were removed, and samples were weighed and measured.
Before impact application, an ultrasonic wave speed measuring device (Ultrasonic Model ELE) was used to measure the speed of transmitted acoustic waves through the tissue. This measurement was performed using the relationship V=L/T(Equation 1), where Lis the probe distance and Tis the wave transit time. A sonography gel was used to improve wave transmission, and the probe direction was perpendicular to the impact plane.
Dynamic impact was applied using a pendulum test at three energy levels (0.015, 0.075, and 0.18 Joules). The low energy levels correspond to transportation bumps, and the higher levels simulate mechanical harvesting impacts. A C304 stainless steel impact surface was installed beneath the pendulum stage to simulate a factory environment.
After impact application, the fruits were treated with a UV-C lamp (wavelength 254 nm) at a distance of 30 cm for control (untreated), 20, 40, and 60 minutes to delay spoilage. The apples were stored in the laboratory environment for 3 and 10 days. Subsequently, the wave transit speed was measured again using ultrasound. Additionally, a texture analyzer (Instron) was used to measure the maximum compression force (up to a depth of 6 mm). Finally, the bruise volume was calculated by peeling the skin at the damaged site and measuring the diameter and depth of the indentation, using the relationship BV=π/6 dD^2.
Analysis of variance (ANOVA) results indicated that all three investigated factors (Impact Energy, UV Irradiation Duration, and Storage Period) had a significant effect at the 99% confidence level on all measured parameters (Puncture Force, Bruise Volume, and Wave Transit Velocity). Furthermore, the pairwise interaction effects of these factors (Impact Energy ×Storage Period, UV ×Storage Period, and Impact Energy ×UV) were also significant on the studied properties. The impact energy level significantly affected all measured characteristics. The highest compressive resistance (puncture force) was observed in the control treatment (no impact) at 43.31 N, while the most severe impact (0.18 J) resulted in the lowest force (15.36 N). Bruise volume also showed an inverse relationship with puncture force; the smallest bruise volume was related to the control, and the largest bruise volume (693.69 〖"mm" 〗^3) was observed at the 0.18 J level. This high-energy level was also associated with the lowest wave transit velocity (138.90 m/s).
Exposure to UV radiation had a significant effect on the puncture test force. The 60-minute treatment showed the most positive effect in preserving fruit firmness, which was accompanied by a decrease in the bruised area and an increase in ultrasonic wave transit velocity (indicating the preservation of internal tissue structure). These findings align with the results of researchers such as Jalili Marandi (1391 [2012/2013]), who state that UV preserves mechanical properties by reducing cell respiration, subsequently maintaining water content. The storage period (up to 10 days) significantly affected all three parameters at the 5% level. With an increase in the storage duration, the lowest puncture force (17.06 N) and wave velocity (141.08 m/s), and consequently, the highest bruise volume (909.65 〖"mm" 〗^3), were observed in the 10-day samples.
Impact Energy ×UV Interaction Effect: The highest force (33.38 N) and wave velocity (192.53 m/s) were recorded under the no-impact treatment combined with 60 minutes of UV irradiation. This suggests that UV radiation can partially mitigate the adverse effects of impact, which is consistent with the results of Mirjalili et al. (1391 [2012/2013]) regarding increased storage life. Conversely, the lowest force (15.45 N) and wave velocity (157.91 m/s) resulted from the combination of 0.18 J impact and zero UV time.
Impact Energy ×Storage Period Interaction Effect: A reduction in force and wave velocity was observed with the simultaneous increase in impact energy and storage duration (lowest force: 11.63 N at 0.18 J and 0 days of storage), aligning with the findings of Sarmayeh et al. (1397). Furthermore, the most severe bruising (1397.83 〖"mm" 〗^3) occurred in the combination of maximum impact (0.18 J) and the longest storage period (10 days).
Overall, the results emphasize that physical stresses (impact) and environmental stresses (UV and time) independently and interactively affect the mechanical quality of apples, and the optimal treatments—including no impact application or prolonged UV exposure—were most effective in preserving firmness and reducing tissue degradation.
The analysis of the interaction effects showed that increasing the impact energy and the storage period continuously caused a decrease in puncture force and sound velocity, and an increase in bruise volume. The highest firmness, at 34.57 N, was achieved under the control conditions combined with 60 minutes of UV-C. UV-C irradiation aids in improving mechanical properties, reducing the rate of bruise increase, and enhancing the shelf life of damaged apples by decreasing respiration.
This research was financially and spiritually supported by the Research Vice-Chancellery of Shahrekord University, Shahrekord, Iran. The study was conducted as part of the M.Sc. thesis of the first author at the Faculty of Agriculture, Shahrekord University.
Conceptualization: Mahdi Ghasemi Varnamkhasti;
Methodology: Mahdi Ghasemi Varnamkhasti, Mojtaba Naderi Boldaji;
Formal analysis: Hossine Ghayour;
Investigation: Hossine Ghayour; Mahdi Ghasemi Varnamkhasti, Mojtaba Naderi Boldaji.
Data curation: Hossine Ghayour; Mahdi Ghasemi Varnamkhasti, Mojtaba Naderi Boldaji.
Writing—original draft preparation: Hossine Ghayour;
Writing—review and editing: Mahdi Ghasemi Varnamkhasti, Mojtaba Naderi Boldaji;
Supervision: Mahdi Ghasemi Varnamkhasti, Mojtaba Naderi Boldaji.
All authors have read and agreed to the published version of the manuscript.
No artificial intelligence tools were used in the article writing process.
The data that support the findings of this study are available from the authors upon reasonable request.
The authors would like to express their sincere appreciation to the Research Vice-Chancellery of Shahrekord University and the Faculty of Agriculture, Shahrekord University for supporting this research.
The authors also thank the anonymous reviewers for their constructive comments and valuable suggestions that improved the quality of this manuscript.
The authors avoided data fabrication, falsification, plagiarism, and any form of scientific misconduct.
The authors declare no conflict of interest.
