Continuous plasma microbubble (PMB) treatment for Escherichia coli inactivation and quality preservation in strawberry, blueberry, and romaine lettuce

Plasma microbubbles (PMB), which combine the antimicrobial activities of gas plasma with the enhanced surface interaction of microbubbles, offer an alternative to conventional sanitizers for mitigating microbial contamination and cross-contamination during postharvest washing of fresh produce. This study evaluated a prototype benchtop-scale PMB system for the inactivation of E. coli TVS355 on strawberries, blueberries, romaine lettuce, and in wash water. A rod-to-mesh dielectric barrier discharge (DBD) reactor ionized compressed air into plasma, which was diffused through water via a microbubble diffuser to generate PMB. Strawberries, blueberries, and romaine lettuce inoculated with E. coli were treated with PMB, microbubble (MB), or distilled water (DW) for 10, 15, and 20 min. PMB achieved significantly greater E. coli reductions on all produce types compared to MB and DW, with up to 1.5 ± 0.4 log CFU/produce on strawberries, 1.9 ± 0.2 log CFU/produce on blueberries, and 2.8 ± 0.2 log CFU/produce on lettuce. In wash water, E. coli was reduced to undetectable levels (<1.0 log CFU/mL), highlighting PMB's potential to prevent cross-contamination. Scanning electron microscopy revealed membrane shrinkage and surface distortion of E. coli cells after PMB exposure. PMB maintained the color, texture, and sensory quality of the produce, and suppressed microbial regrowth during 24-h storage. These findings demonstrate that PMB is a non-thermal technology with strong potential for postharvest decontamination, and performance under organic loading conditions requires further evaluation.