Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: INTERVENTION TECHNOLOGIES FOR MINIMALLY PROCESSED FOODS

Location: Food Safety and Intervention Technologies

Title: Cold plasma reduction of Salmonella and Escherichia coli 0157:H7 on almonds using ambient pressure gases

Authors
item NIEMIRA, BRENDAN
item BOYD, GLENN

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2011
Publication Date: January 20, 2012
Citation: Niemira, B.A., Boyd, G. 2012. Cold plasma reduction of Salmonella and Escherichia coli 0157:H7 on almonds using ambient pressure gases. Journal of Food Science. 77:M171-175.

Interpretive Summary: Contamination of raw nuts, including almonds, is a food safety concern. Cold plasma is a novel antimicrobial intervention that can eliminate foodborne pathogens. The objective of this work was to evaluate the efficacy of rapid cold plasma treatments in eliminating Salmonella and Escherichia coli O157:H7 from dry almonds. Three isolates of Salmonella and three isolates of E. coli O157:H7 were separately grown and inoculated onto whole almonds. Inoculation spots were allowed to dry for 10 minutes. Inoculated almonds were positioned under a stream of cold plasma generated using a modified commercial plasma jet emitter. Three treatment variables were evaluated in a factorial design for each isolate: time, distance and feed gas. Treatment time was 0s (control), 10s or 20s. Distance from the emitter was 2, 4 or 6 cm. Feed gas was either dry air or pure nitrogen. After treatment, the almonds were sampled using swabs, and survivors were enumerated on TSA plates. Cold plasma significantly reduced both pathogens on almonds. The greatest reduction observed was 1.34 log cfu/ml reduction of one of the isolates of E. coli O157:H7 after 20s treatment at 6 cm spacing. The interaction of treatment time with distance from plasma emitter head was complex, and isolate-dependent. Longer duration of treatment did not always results in enhanced reductions. In general, nitrogen as a feed gas resulted in a reduced antimicrobial efficacy compared to dry air. These results indicate that short pulses of atmospheric pressure cold plasma can significantly reduce Salmonella and E. coli O157:H7 on almonds. This dry, nonthermal, chemical-free process holds promise for future research into methods to make almonds and other nuts safer for consumers.

Technical Abstract: Contamination of raw nuts, including almonds, is a food safety concern. Cold plasma is a novel antimicrobial intervention that can eliminate foodborne pathogens. The objective of this work was to evaluate the efficacy of rapid cold plasma treatments in eliminating Salmonella and Escherichia coli O157:H7 from dry almonds. Three isolates of Salmonella (S. Anatum F4317, S. Stanley H0558, and S. Enteritidis PT30) and three isolates of E. coli O157:H7 (C9490, ATCC 35150, and ATCC 43894) were separately grown and spot-inoculated (10 µl) onto whole almonds. Inoculation spots were allowed to dry for 10 minutes. Inoculated almonds were positioned under a stream of cold plasma generated using a modified commercial plasma jet emitter. For each isolate, three treatment variables were evaluated in a factorial design for each isolate: time, distance and feed gas. Treatment time was 0s (control), 10s or 20s. Distance from the emitter was 2, 4 or 6 cm. Feed gas was either dry air or pure nitrogen. After treatment, the almonds were sampled using swabs, and survivors were enumerated on TSA plates. Cold plasma significantly reduced both pathogens on almonds. The greatest reduction observed was 1.34 log cfu/ml reduction of E. coli O157:H7 C9490 after 20s treatment at 6cm spacing. The interaction of treatment time with distance from plasma emitter head was complex, and isolate-dependent. Longer duration of treatment did not always results in enhanced reductions. In general, nitrogen as a feed gas resulted in a reduced antimicrobial efficacy compared to dry air. These results indicate that short pulses of atmospheric pressure cold plasma can significantly reduce Salmonella and E. coli O157:H7 on almonds.

Last Modified: 9/29/2014