The impact of cold atmospheric plasmas on microbialy contaminated raw plant foods

A considerable body of data has been accumulated in recent years attesting to the efficacy of cold atmospheric plasmas in inactivating microorganisms on the surfaces of abiotic materials such as glass and synthetic membranes. However, one novel application for such plasmas is in microbially decontaminating foods such as fruits and vegetables which are served raw, and for which there are currently no effective methods of rendering them microbiologically safe. The flesh of most plant foods is generally free of microorganisms immediately in the period after harvesting. It is only when fresh produce is cut and subsequently processed that the potential for contamination, and the concomitant threat to human health, starts to increase considerably. Plant cells are complex structures, and their physical arrangement or stacking provides channels through which microorganisms originally present on the surface can become internalized. It is crucial to have knowledge of the rate at which this process of internalization occurs so that a decontamination technology can be selected that can inactivate microbial cells before they migrate too far away from the surface. Fluorescence microscopy was used to measure the rate of migration of a variety of spoilage organisms and pathogens into the flesh of cantaloupe melons. Microbially contaminated melon pieces were then treated with a dielectric barrier discharge (DBD) plasma operating at tens of kHz. Three dimensional images were obtained which shows both the effect of the plasma on the plant cells and, through the use of viability stains, the impact on microorganisms at various depths into the flesh of the melon. It is concluded that plasma treatment may serve as a viable food decontamination technology provided that the timing of treatment is carefully integrated into the processing of plant foods.