UVC LED System for Prolonging the Postharvest Shelf Life of Murcotts

Optics Environmental Engineering Engineering Botany Life Sciences Physics Bioengineering
UVC technology fruit preservation murcott optical system green mold

Academic Background

Citrus fruits have long been favored by consumers for their rich nutritional value and unique flavor. However, citrus fruits are highly susceptible to diseases during postharvest storage, particularly green mold caused by Penicillium digitatum. This disease leads to fruit decay and significantly shortens storage life. Traditionally, chemical fungicides have been widely used to control green mold, but due to potential health and environmental threats from chemical residues, non-chemical alternative methods have gradually become a research hotspot.

In recent years, physical treatment technologies have gained attention for their residue-free and eco-friendly characteristics. Among them, ultraviolet C (UVC, wavelength 200–280 nm) radiation is considered a promising solution. UVC can inhibit disease development by destroying the DNA of pathogens, while also enhancing fruit resistance and delaying ripening. However, although studies have shown that UVC can effectively reduce the occurrence of citrus green mold, its commercial application still faces many challenges, such as issues with light uniformity and dose control. To address these problems, this study aims to design an optical system based on UVC LEDs, optimize light distribution uniformity, and evaluate its practical effectiveness in Murcott citrus preservation.

Source of the Paper

This paper was authored by Le Thi-Thi-Ngoc and her team, with authors from the Department of Optics and Photonics at National Central University, the Crop Environment Section of Taichung District Agricultural Research and Extension Station, and the Department of Electrophysics at National Yang-Ming Chiao Tung University in Taiwan. The paper was published in 2025 in the journal Optical and Quantum Electronics, article number 57:161, DOI: 10.1007/s11082-025-08071-w.

Research Process

a) Experimental Design and Workflow

This study mainly includes the following steps:

1. Optical Modeling and System Design

The study first selected UVC LEDs with a wavelength of 275 nm as the light source, which achieved an output power of 50 mW when the current was 0.350 A. To improve light distribution uniformity, the research team equipped each LED with a dome lens to narrow the divergence angle. By combining fluorescent film experiments with the Monte-Carlo ray-tracing method, the researchers established an accurate LED optical model and applied it to system design.

The final design included a 4×4 array of UVC LEDs, with each LED corresponding to one Murcott citrus fruit. The entire optical module was positioned 23 cm above the target area, which measured 34×34 cm². The system also featured an aluminum cavity to reduce heat issues and ensure concentrated light irradiation on the target area.

2. Irradiance Monitoring and Analysis

To verify the system’s performance, researchers measured the irradiance distribution in the target area through both simulation and experimentation. Specifically, they used a power meter detector to record irradiance values at different positions in the target area and calculated uniformity and optical utilization factor (OUF). Results showed that in the simulation, uniformity reached 85.4%, and OUF was 80.2%; in the experiment, uniformity was 77.2%, indicating high optical performance of the system.

Additionally, the study tested the system’s flexibility by turning off LEDs at specific positions. Results showed that even when some LEDs were turned off, the remaining LEDs could still ensure uniform irradiation within the target area.

3. Effect of UVC Treatment on Penicillium digitatum (In Vitro Experiment)

To evaluate the inhibitory effect of UVC on P. digitatum, researchers exposed spore suspensions of P. digitatum to varying doses of UVC (0.00 to 1.50 kJ/m²). After 24 hours of incubation, spore germination was observed; after 72 hours, colony formation was counted. Results indicated that when the UVC dose exceeded 0.3 kJ/m², spore growth was significantly inhibited, with an inhibition rate exceeding 90%.

4. Effect of UVC Treatment on Murcott Citrus (In Vivo Experiment)

Researchers selected different groups of Murcott citrus fruits and subjected them to UVC treatments ranging from 0 to 20 minutes, corresponding to UVC doses of 0.00 to 6.00 kJ/m². After treatment, the citrus fruits were stored under room temperature conditions, and their disease severity index (DSI) was assessed regularly. Results showed that UVC doses in the range of 0.9 to 4.5 kJ/m² effectively maintained citrus quality for up to four weeks, with the optimal dose being 1.5 kJ/m².

b) Main Results

1. Optical Performance

Within the target area, the system’s irradiance distribution ranged between 3 to 5 W/m², with uniformity reaching 85.4% in simulations and 77.2% in experiments. This indicates that the system can efficiently concentrate light in the target area while maintaining high uniformity.

2. Inhibitory Effect on Penicillium digitatum

In vitro experiments showed that when the UVC dose exceeded 0.3 kJ/m², the growth of P. digitatum spores was significantly inhibited, with an inhibition rate exceeding 90%. This result verifies the effective sterilization capability of UVC on pathogens.

3. Preservation Effect on Murcott Citrus

In vivo experiments demonstrated that UVC treatment significantly reduced the incidence of green mold on Murcott citrus. Within the dose range of 0.9 to 4.5 kJ/m², the disease severity index (DSI) of citrus remained below 10% over four weeks. However, excessively high UVC doses (e.g., 6.0 kJ/m²) did not further improve preservation effects but instead may lead to energy waste.

c) Conclusions and Significance

This study shows that an optical system based on UVC LEDs can effectively extend the postharvest shelf life of Murcott citrus. The system not only has high optical performance but can also be flexibly adjusted to adapt to different application scenarios. Additionally, the study reveals the relationship between UVC dose and preservation effects, providing important references for future optimization of UVC treatments.

From a scientific perspective, this research fills the gap in the application of UVC technology in citrus preservation, laying the groundwork for subsequent studies. From an application standpoint, the system has advantages such as low cost, simple operation, and easy maintenance, making it suitable for large-scale commercial promotion.

d) Highlights of the Study

  1. Innovative Optical Design: Optimized light distribution through dome lenses significantly improved irradiance uniformity.
  2. Flexible Application Scenarios: The system can be intelligently integrated into automated controls, selectively turning LEDs on or off based on actual needs.
  3. Clear Dosage Guidance: The study clarified the relationship between UVC dose and preservation effects, providing a scientific basis for practical applications.
  4. Multi-dimensional Verification: Comprehensive verification of UVC effects through in vitro and in vivo experiments enhanced the reliability of conclusions.

e) Other Valuable Information

The research team also proposed that future studies should further explore the preservation effects of UVC on other fruits, as well as changes in microbial resistance and repair mechanisms during long-term storage. Additionally, combining UVC with other preservation technologies (such as cold storage) may further enhance preservation effects.