Cold plasma and pulsed light inactivates Escherichia coli O157:H7 in Romaine lettuce and preserves produce quality

Authors: Mukhopadhyay, Sudarsan; Niemira, Brendan; Ukuku, Dike; Olanya, Modesto; Boyd, Glenn; Jin, Zhonglin; Fan, Xuetong

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2024
Publication Date: 11/13/2024
Citation: Mukhopadhyay, S., Niemira, B.A., Ukuku, D.O., Olanya, O.M., Boyd, G., Jin, Z.T., Fan, X. 2024. Cold plasma and pulsed light inactivates Escherichia coli O157:H7 in Romaine lettuce and preserves produce quality. Journal of Food Safety. 44(6):e70000. http://dx.doi.org/10.1111/jfs.70000.
DOI: https://doi.org/10.1111/jfs.70000

Interpretive Summary: Microbial safety of produce continues to pose a major challenge. Leafy greens like Romaine lettuce have been frequently implicated in outbreaks in recent years. To tackle the issue, the produce industry uses chlorine-based sanitizer washes whose efficacy is limited and safety is questionable. Novel, safe, and effective methods are needed. We developed a method combining pulsed light and cold plasma treatments to combat the challenge. This combination drastically reduces treatment time and hence minimizes product temperature rise while providing mandated levels of decontamination without harming product quality. This purely nonaqueous, chemical free, sustainable clean technology demonstrated capability of killing pathogens like E. coli O157:H7 by greater than 99.999% to enhance safety, quality, and shelf life of fresh produce like Romine lettuce. This clean technology holds a great promise for market implementation.

Technical Abstract: Contamination of fresh produce with bacterial pathogens continues to be a major concern. Novel antimicrobial intervention technologies are needed to lessen the threat of contamination. This study investigated the antimicrobial efficacy of cold plasma (CP), pulsed light (PL) and their optimized combinations for inactivating Escherichia coli O157:H7 in Romaine lettuce. Treatment influence on native microbiota and sensory quality of lettuce was also investigated during cold storage for 7 days at 4 degree C. An inoculum consisting of bacterial composite of three outbreak strains of E. coli O157:H7 was used for this study. Lettuce leaves were spot inoculated before treating with PL (1-60 s), CP (15-60 s) or their optimized treatment combinations. PL treatment for 30 s, equivalent to fluence dose of 31.5 J per square cm, was optimal and provided 2.7 log CFU/g reduction of E. coli O157:H7, while 45 s treatment of CP was optimum, which delivered slightly lower inactivation of 2.1 log CFU/g. Combination of PL and CP treatments sequences were explored to investigate enhanced inactivation. In PL-CP combination, inoculated lettuce was treated with PL for 30 s followed by 45 s of CP exposure. Whereas for CP-PL combination, inoculated lettuce was subjected to 45 s of CP treatment prior to 30 s of PL treatment. Both combination treatments (PL-CP and CP-PL) provided synergistic inactivation of the pathogen, as no E. coli cells were detectable after treatment, indicating >5 log reductions of the pathogen. The combination treatments not only significantly (P <0.05) reduced native microbiota of Romaine lettuce but also slowed their growth during storage. Furthermore, the quality of lettuce was not significantly affected by these combination treatments. PL and CP are both nonaqueous, sustainable technologies. Overall, our results demonstrated that integrated PL and CP technology can enhance microbial safety and preserve the quality of Romaine lettuce.