Plasma inactivation of bacterial endospores on wheat grains and polymeric model substrates in a dielectric barrier discharge

Abstract

Motivated by the frequent microbial contamination of granular food products like cereal grains or sprout seeds, an atmospheric pressure dielectric barrier discharge (DBD) was developed to study plasma inactivation of microorganisms on granular materials. Wheat grains as well as polypropylene model substrates were artificially contaminated with endospores of Geobacillus stearothermophilus as a model organism and treated in a pulsed argon plasma discharge applying different combinations of treatment time, pulse voltage and frequency. While the treatment of polypropylene substrates resulted in an efficient reduction of microbes, wheat grains, having a rough surface and a deep ventral furrow, turned out to be more challenging to decontaminate. However, an improvement in treatment efficiency could be achieved by applying longer treatment, faster pulse frequency or higher pulse voltage. Furthermore, experiments demonstrated that endospore reduction was not caused by thermal, mechanical or electrical stress factors, but a direct effect of plasma-generated species, and chemical sputtering is supposed to be the predominant inactivation mechanism. Finally, it could be shown that functional wheat grain properties (Falling number, gluten content) are not negatively affected by our plasma treatment.