Cold Plasma Inactivates Salmonella Stanley and Escherichia coli O157:H7 Inoculated on Golden Delicious Apples

Authors: Niemira, Brendan; Sites, Joseph

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2008
Publication Date: 7/4/2008
Citation: Niemira, B.A., Sites, J.E. 2008. Cold Plasma Inactivates Salmonella Stanley and Escherichia coli O157:H7 Inoculated on Golden Delicious Apples. Journal of Food Protection. 71(7):1357-1365.

Interpretive Summary: Cold plasma is a novel sanitizing technology that uses high-energy, reactive gases to inactivate pathogens on foods such as fresh produce. Cold plasma was produced by a high voltage gliding arc system, which allows for physical separation of plasma generation and deposition. Dried, filtered air was used as the feed gas and ionization medium. The resulting plasma, at ambient temperature and pressure, was used to treat the outbreak strains Escherichia coli O157:H7 ATCC 43894 and Salmonella Stanley H0558 on agar plates and inoculated onto the surfaces of golden delicious apples. In treatments of spread-inoculated agar plates, cold plasma inactivated both pathogens. Higher flow rate (40 L/min) was more efficacious than lower (20 L/min), irrespective of treatment time (1 or 2 minutes). In tests with golden delicious apples, spot inoculations of either pathogen onto the surface were allowed to dry for 2h. and then treated with combinations of various flow rates for various times. All treatments resulted in significant (p<0.05) reductions from the untreated control. These results indicate that cold plasma is a nonthermal process that can effectively reduce human pathogens inoculated onto fresh produce.

Technical Abstract: Cold plasma generated in a gliding arc was applied to outbreak strains of Escherichia coli O157:H7 and Salmonella Stanley on agar plates and inoculated onto the surfaces of golden delicious apples. This novel sanitizing technology inactivated both pathogens on agar plates, with higher flow rate (40 L/min) observed to be more efficacious than lower (20 L/min), irrespective of treatment time (1 or 2 minutes). Golden delicious apples were treated with cold plasma at various flow rates (10, 20, 30 or 40 L/min) for various times (1, 2 or 3 minutes), applied to dried spot inoculations. All treatments resulted in significant (p<0.05) reductions from the untreated control, with 40L/min more effective than lower flow rates. Inactivation of S. Stanley followed a time-dependent reduction for all flow rates. Reductions after 3 minutes ranged from 2.9 to 3.7 log cfu, close to the limit of detection. For E. coli O157:H7, 40 L/min gave similar reductions for all treatment times, 3.4 - 3.6 log cfu. At lower flow rates inactivation was related to exposure time, with 3 minutes resulting reductions of 2.6 - 3.0 log cfu. Temperature increase of the treated apples was related to exposure time for all flow rates. The maximum temperature of any plasma treated apple was 50.8C (28C above ambient), following 20 L/min for 3 minutes. These results indicate that cold plasma is a nonthermal process that can effectively reduce human pathogens inoculated onto fresh produce.