Conformable Surface Dielectric Barrier Discharge Plasma Treatment of Fresh Produce: Evaluation of Microbial Inactivation Efficacy and Quality Attributes

Conformable plasma electrodes offer the advantages of being bendable, lightweight and has the potential for high local concentrations of plasma to interact with exterior surfaces being treated, which are expected to benefit future applications in the food industry. In this study, plasma generated using conformable surface dielectric barrier discharge (SDBD) electrodes made by metallized paper was evaluated for its antimicrobial activity and effects on quality attributes of fresh tomato and baby spinach. Two conformable SDBD systems were prepared: a two-cone configuration of electrodes was used for plasma treatment of tomatoes while the flat circular design was used for spinach leaves. Following plasma treatment for 2 min, 5 min, and 10 min, reductions of 2.7±0.6 log CFU/tomato, 3.9±0.3 log CFU/tomato, and 5.2±0.2 log CFU/tomato of E. coli population were achieved on tomato surface, while 2.5±0.1 log CFU/leaf, 2.7±0.9 log CFU/leaf, and 2.9±0.9 log CFU/leaf reduction was achieved on the surface of baby spinach. The firmness of the treated tomato and spinach, evaluated using puncture analysis, revealed no significant difference (p > 0.05) in either spinach or tomato treated for 2 min, 5 min, or 10 min compared with untreated control. While no changes in color and visual appearance were observed in treated tomatoes, regional darkening of the spinach leaves was observed. The results demonstrate that the flexible plasma SDBD electrodes are effective as a potential decontamination technique on the food surface. The variation in inactivation between tomato and spinach indicates that the conformability of the SDBD electrodes and the surface properties of food play an important role in affecting the decontamination efficacy. In addition, optimization of the flexible plasma SDBD is needed to maximize the reactive species concentration to achieve microbial inactivation while preserving the quality attributes of treated food.