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Front. Microbiol. | doi: 10.3389/fmicb.2018.03164

Characterization of Efficiency and Mechanisms of Cold Atmospheric Pressure Plasma Decontamination of Seeds for Sprout Production

 Alexandra Waskow1, Julian Betschart2,  Denis Butscher2, Gina Oberbossel2, Denise Klöti3,  Annette Büttner-Mainik3, Jozef Adamcik2, Philipp Rudolf von Rohr2 and  Markus Schuppler2*
  • 1École Polytechnique Fédérale de Lausanne, Switzerland
  • 2ETH Zürich, Switzerland
  • 3Agroscope, Switzerland

The consumption of fresh fruit and vegetable products has strongly increased during the past few decades. However, inherent to all minimally processed products is the short shelf life, and the risk of foodborne diseases, which have been increasingly related to such products in many parts of the world. Because of the favorable conditions for the growth of bacteria during the germination of seeds, sprouts are a frequent source for pathogenic bacteria, thus highlighting the need for seed decontamination to reduce the risk of foodborne illness. Consequently, this study focused on cold atmospheric pressure plasma treatment of artificially inoculated seeds in a diffuse coplanar surface barrier discharge to determine the inactivation efficiency for relevant foodborne pathogens and fungal spores. Plasma treatment of seeds resulted in a highly efficient reduction of microorganisms on the seed surface, while preserving the germination properties of seeds, at least for moderate treatment times. To better characterize the mechanisms that contribute to microbial inactivation during plasma treatment, an experimental setup was used that facilitated the separate investigation of UV and other plasma components. The combination of life/dead staining methods with confocal laser scanning microscopy analysis revealed a less efficient inactivation of bacteria by ozone and other reactive species generated during plasma treatment compared to UV. Further characterization of the effect of cold atmospheric pressure plasma on bacterial cells was performed by atomic force microscopy imaging of identical E. coli cells before and after treatment. The impact of plasma treatment on bacterial cells was demonstrated by an increase in surface roughness and visible indentations on the bacterial cell surface that suggest a physical damage of the cell envelope. In conclusion, cold atmospheric pressure plasma shows potential for being a relevant decontamination technology in the production process of sprouts, which may contribute to food safety and prolonged shelf life of the product.

Keywords: Cold atmospheric pressure plasma, Seed decontamination, Sprout production, Atomic force micorscopy (AFM), dielectric coplanar surface barrier discharge

Received: 15 Jul 2018; Accepted: 06 Dec 2018.

Edited by:

Kai Reineke, GNT Europa GmbH, Germany

Reviewed by:

Christopher Doona, Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, United States
Dusan Kovacik, Comenius University, Slovakia  

Copyright: © 2018 Waskow, Betschart, Butscher, Oberbossel, Klöti, Büttner-Mainik, Adamcik, Rudolf von Rohr and Schuppler. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Markus Schuppler, ETH Zürich, Zurich, 8092, Zürich, Switzerland, markus.schuppler@ethz.ch