Modelling and optimisation of VUV photolysis for ethylene control: for potential application in postharvest management

Abstract

Fresh horticultural produce faces considerable postharvest losses, ranging from 30 to 44%, primarily due to the highly perishable nature of these goods. Among the various contributors to these losses, ethylene emerges as a key factor, triggering and accelerating fruit ripening, leading to softening, senescence, and an overall decline in quality. Effective control of ethylene during postharvest handling and storage is crucial for extending fruit shelf life, maintaining fruit quality, and promoting sustainable agricultural practices. Various methods, including ozone treatment, low-temperature storage, bio-filtration, and potassium permanganate (KMnO4), have been explored to mitigate ethylene's impact. However, these methods often have limitations that affect their long-term applicability, and their efficacy in maintaining fruit and vegetable quality varies. Additionally, there is a gap in understanding these technologies' effects on microbial activity. This study aimed to evaluate the efficacy of a vacuum ultraviolet (VUV) photolysis reactor for ethylene removal in fruit storage and its subsequent impact on microbial activity responsible for rapid ripening. Specific objectives included investigating ethylene degradation kinetics using a VUV photolysis reactor, assessing the potential of VUV photolysis for ethylene removal in mixed-fruit storage at room temperature, examining the impact of direct VUV radiation on apples' physiological parameters at 15 °C, and exploring proteomic changes related to ethylene removal by VUV photolysis and its effects on apple ripening during postharvest storage. To achieve these objectives, a VUV photolysis reactor was developed and used in experiments to remove ethylene from fruit storage. The first experiment compared the VUV photolysis reactor with the standard fruit industry adsorbent, potassium permanganate (KMnO4), for ethylene removal from mixed-fruit storage (apples, bananas, and pears) at ambient temperature (16 °C) for 6 days. The second study evaluated the impact of direct VUV radiation on the quality attributes of apples stored at 10 °C for 21 days. Results showed that ethylene levels in mixed-fruit storage were significantly reduced by 86.9 % with the VUV reactor, compared to 25.4 % with potassium permanganate. Direct VUV exposure effectively reduced ethylene and respiration rates but caused some skin damage to the apples. Apples in control storage lost firmness at a rate 2.3 times higher, while VUV photolysis extended apple shelf life by 46 days. The potential of a VUV photolysis reactor for ethylene removal during postharvest storage and its effect on proteomic changes in apple fruit stored at 15 °C for 28 days was investigated. A total of 441 differentially expressed proteins (DEPs) were identified, with 336 proteins in fresh apple samples (on day 0), and 287 and 396 proteins in the treatment and control groups, respectively, after 28 days of storage. Proteins responsible for cell wall modification and ethylene synthesis were upregulated in the control group, while VUV photolysis significantly downregulated proteins associated with cell wall degradation and ethylene synthesis. The degradation kinetics of ethylene were investigated at different light intensities (0.0005 mW/m², 0.0014 mW/m², and 0.0021 mW/m²) and relative humidity (RH) levels (20 % and 80 %), and the economic feasibility of the VUV photolysis system was evaluated. The results showed that ethylene degradation increased with higher light intensity. Additionally, high relative humidity favoured ethylene degradation. Both light intensity and RH significantly influenced the kinetic parameters and degradation of ethylene (p < 0.05). At low light intensity, ethylene degradation followed a zero-order kinetic model, while at high intensity, it followed a fractional-order kinetic model, indicating a possible change in the reaction mechanism. The economic feasibility of the VUV photolysis system was evaluated using electrical energy per order (EEO), which remained below 10 kW m⁻³ order⁻¹, indicating both energy efficiency and practical applicability. A mathematical model was developed to optimize the VUV photolysis reactor and simulate the temperature variation inside it. The developed mass balance model successfully predicted the experimental ethylene concentrations with R² values above 0.9. Although the energy balance model underestimated the temperature variation inside the reactor, it accurately captured the overall trend in temperature increase, demonstrating the model's feasibility. A sensitivity analysis was performed to investigate critical factors affecting the design and optimization of the VUV photolysis reactor. Light intensity and reactor length were found to have the most significant impact on ethylene degradation. Increasing light intensity and decreasing reactor length improved removal efficiency. In conclusion, this study highlights the significant potential of VUV photolysis as an innovative technique for ethylene removal during the transportation and storage of fruits and vegetables. The findings suggest that VUV photolysis is a promising tool for postharvest management, offering an effective solution to preserve fruit quality and reduce horticultural supply chain losses. Future research should focus on optimizing exposure conditions, designing ozone scrubbers, and refining kinetic models to enhance the practical implementation of this technology.