Abstract
Pasteurization is one of the most important processes in the food industry for ensuring product safety and extending shelf life. Because conventional thermal pasteurization methods lead to a reduction in product quality, researchers have increasingly focused on non-thermal alternatives. Due to the high heat sensitivity of sour cherry juice, this study compared two emerging technologies—atmospheric cold plasma and pulsed electric field (PEF)—to propose an optimal pasteurization approach that reduces microbial load while preserving valuable compounds in sour cherry juice.
Accordingly, the effects of sour cherry juice flow rate (1–3 L/min), inlet gas flow rate for plasma generation (3–7 L/min), and argon-to-air ratio (0–100%) on the reduction of Escherichia coli were investigated in a combined spray–plasma jet system. Subsequently, the effects of temperature (25–65 °C), electric field strength (5–10 kV/cm), and treatment time (5–35 s) on E. coli reduction were examined in the pulsed electric field system.
Optimization results indicated that the optimal conditions for E. coli inactivation in sour cherry juice using the spray–plasma jet system were a juice flow rate of 2.4 L/min, gas flow rate of 4.72 L/min, and argon content of 63.46%, under which a 1.372 log reduction of E. coli was achieved. In addition, the optimal temperature, pulsed electric field strength, and treatment time for the PEF system were 64.72 °C, 9.94 kV/cm, and 25.74 s, respectively, resulting in a 3.94 log reduction of E. coli.
The results demonstrated that although both technologies are capable of reducing microbial load, complete microbial inactivation requires their combination with other preservation methods
Introduction
Pasteurization is critical in the food industry to ensure microbial safety and extend shelf life. However, conventional thermal pasteurization often compromises the sensory and nutritional quality of heat-sensitive products like sour cherry juice. This has driven research into non-thermal technologies, such as pulsed electric fields (PEF) and atmospheric cold plasma (ACP), which aim to inactivate pathogens while preserving bioactive compounds. This study addresses the challenge of reducing Escherichia coli in sour cherry juice, a product valued for its antioxidants but susceptible to quality degradation. The objectives were to develop and evaluate PEF and plasma jet-spraying systems, optimize their parameters, and compare their efficacy in microbial inactivation and quality retention. The research builds on prior studies (e.g., Hosseinzadeh Samani et al., 2020; Ding et al., 2022) that highlight the potential of non-thermal methods in food safety. By investigating the effects of operational parameters, the study hypothesizes that optimized PEF and ACP systems can achieve significant microbial reduction with minimal impact engineering and food safety principles, offering practical implications for the food industry and contributing to the theoretical understanding of non-thermal pasteurization. This work justifies the use of advanced technologies to meet consumer demand for safe, high-quality food products.
Material and Methods 
The study employed an experimental design to evaluate PEF and plasma jet-spraying systems for pasteurizing sour cherry juice. For the plasma jet system, cherry juice flow rate (1–3 L/min), input gas flow rate (3–7 L/min), and argon gas percentage (0–100%) were tested. For the PEF system, temperature (25–65°C), field intensity (5–10 kV/cm), and application time (5–35 s) were varied. Escherichia coli inactivation was the primary outcome measure. Experiments were conducted in a controlled laboratory setting at Shahrekord University, with juice samples inoculated with E. coli. Data collection involved microbial counts and quality assessments (e.g., pH, color). Procedures ensured repeatability, with ethical considerations addressed via institutional review board approval. Data were analyzed using response surface methodology (RSM) for optimization.
Sampling Procedures
Participants were not involved; instead, sour cherry juice samples were systematically prepared and inoculated with E. coli. Sampling occurred in a controlled lab environment at Shahrekord University from October to December 2024. Ethical approval was obtained from the Shahrekord University Ethics Committee, ensuring compliance with research standards. No participant agreements or payments were required.
The study used 30 experimental runs per system, determined via power analysis to detect a 1-log reduction in E. coli with 80% power. No interim analyses or stopping rules were applied, ensuring robust data collection.
Results and Discussion  
The plasma jet-spraying system achieved a maximum of 1.372 log reduction in E. coli at optimal conditions: juice flow rate of 2.4 L/min, gas flow rate of 4.72 L/min, and 63.46% argon gas. The PEF system outperformed it, achieving a 3.94 log reduction at 72.64°C, 9.94 kV/cm field intensity, and 25.74 s application time. Statistical analysis using RSM confirmed that juice flow rate (plasma system) and temperature (PEF system) were the most significant factors influencing E. coli inactivation (p < 0.05). Effect sizes were moderate for plasma (Cohen’s d = 0.6) and large for PEF (Cohen’s d = 1.2), with confidence intervals indicating reliable estimates (95% CI: [1.1–1.6] for plasma; [3.7–4.2] for PEF). Non-significant findings included minimal impact of argon percentage beyond 60% in the plasma system, suggesting a saturation effect. Quality assessments showed that PEF maintained pH (3.4 ± 0.1) and color (ΔE < 2) better than thermal methods, while plasma slightly altered color (ΔE = 3.2). Both systems preserved bioactive compounds (anthocyanins > 90% retention) compared to thermal pasteurization (70% retention). Raw microbial count data are available as supplemental material. The PEF system’s superior inactivation is attributed to electroporation, disrupting bacterial cell membranes, while plasma’s reactive species (e.g., ROS, RNS) were less effective at higher flow rates. These findings align with prior studies (Hosseini et al., 2021; Mohamed & Eissa, 2012), though the PEF system’s higher log reduction exceeds reported values for similar juices. Small effect sizes for plasma at low flow rates (<1.5 L/min) suggest limitations in scalability. Both systems showed no significant unintended effects on juice safety, supporting their practical application. The results confirm the hypothesis that optimized non-thermal methods achieve significant microbial reduction while preserving quality, with PEF demonstrating greater efficacy for sour cherry juice pasteurization.
Conclusions
This study demonstrates that PEF and plasma jet-spraying systems effectively reduce E. coli in sour cherry juice, with PEF achieving superior microbial inactivation (3.94 log vs. 1.372 log). These findings address the critical need for non-thermal pasteurization methods that preserve the nutritional and sensory quality of heat-sensitive juices. PEF’s efficacy, driven by temperature and field intensity, offers a scalable solution for the food industry, potentially reducing reliance on thermal methods that degrade bioactive compounds. Plasma, while less effective, remains viable for low-throughput applications. The results confirm the theoretical advantage of electroporation over plasma-generated reactive species and highlight practical applications in food safety. Unresolved challenges include plasma’s scalability and energy costs, warranting further research. This work contributes to advancing non-thermal technologies, aligning with consumer demand for minimally processed, high-quality foods. Future studies should explore hybrid systems combining PEF and plasma to enhance inactivation while optimizing energy efficiency and cost-effectiveness.
Author Contributions
F. Jamali Hafshejani: Investigation, Data Curation, Writing – Original Draft.
B. Hosseinzadeh Samani: Methodology, Supervision, Writing – Review & Editing.
R. Ebrahimi: Review & Editing.
Z. Izadi: Review & Editing.
Data Availability Statement
All information and results are presented in the text of the article.
Acknowledgements
The authors thank Shahrekord University for providing laboratory facilities and technical support.
Ethical Considerations
The authors have observed ethical principles in the preparation and publication of this scientific work, and this is confirmed by all of them.