Inactivation of Escherichia coli 0157:H7 and aerobic microorganisms in Romaine lettuce packaged in a commercial polyethylene terephthalate container using atmospheric cold plasma

Authors: MIN, SEA CHEOL - Seoul Women'S University; ROH, SI HYEON - Seoul Women'S University; Boyd, Glenn; Sites, Joseph; Uknalis, Joseph; Fan, Xuetong; Niemira, Brendan

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2016
Publication Date: 1/1/2017
Citation: Min, S., Roh, S., Boyd, G., Sites, J.E., Uknalis, J., Fan, X., Niemira, B.A. 2017. Inactivation of Escherichia coli 0157:H7 and aerobic microorganisms in Romaine lettuce packaged in a commercial polyethylene terephthalate container using atmospheric cold plasma. Journal of Food Protection. 80(1):35-43.

Interpretive Summary: Leafy greens can be contaminated with human pathogens, but there are few treatments that can be employed after the product is in a commercial package. This study evaluated cold plasma as a treatment for the inactivation of the pathogen Escherichia coli O157:H7 and aerobic microorganisms in Romaine lettuce packaged in a conventional commercial plastic container. The study was conducted during storage at 4C for 7 days. Romaine lettuce pieces, with or without inoculation with a cocktail of three strains of E. coli O157:H7 (approximately 6 log CFU/g lettuce), were packaged in a polyethylene terephthalate commercial “clear clamshell” type container and treated at cold plasma generated by 47.2 kV at 1.1 kHz for 5 min using a pin-type high-voltage electrode. Romaine lettuce samples were analyzed for inactivation of E. coli O157:H7, total mesophilic aerobes, and yeasts and molds. Leaves were also evaluated for color, respiration, weight (i.e. water content), and surface morphology during storage. The cold plasma treatment reduced the initial counts of E. coli O157:H7 and total aerobic microorganisms by ~90%, with negligible temperature change. The reductions in the numbers of E. coli O157:H7, total mesophilic aerobes, and yeasts and molds during storage were 84-97%, 80-99% and 87-98%, respectively. Cold plasma treatment did not significantly affect the color, respiration, water content or surface morphology of lettuce during storage. Some mesophilic aerobic bacteria were sublethally injured by cold plasma. This study demonstrates the potential of applying cold plasma as a post-packaging treatment to decontaminate lettuce contained in conventional plastic packages without altering leaf sensory quality.

Technical Abstract: The effects of dielectric barrier discharge atmospheric cold plasma (DACP) treatment on the inactivation of Escherichia coli O157:H7 and aerobic microorganisms in Romaine lettuce packaged in a conventional commercial plastic container were evaluated during storage at 4 degrees C for 7 days. Effects investigated included the color, carbon dioxide (CO2) generation, weight loss, and surface morphology of the lettuce during storage. Romaine lettuce pieces, with or without inoculation with a cocktail of three strains of E. coli O157:H7 (approximately 6 log CFU/g lettuce), were packaged in a polyethylene terephthalate commercial clamshell container and treated at 47.2 kV at 1.1 kHz for 5 min using an DACP treatment system equipped with a pin-type high-voltage electrode. Romaine lettuce samples were analyzed for inactivation of E. coli O157:H7, total mesophilic aerobes, and yeasts and molds, color, CO2 generation, weight loss, and surface morphology during storage at 4 degrees C for 7 days. The DACP treatment reduced the initial counts of E. coli O157:H7 and total aerobic microorganisms by approximately 1 log CFU/g, with negligible temperature change from 24.5 +/- 1.4 to 26.6 +/- 1.7 degrees C. The reductions in the numbers of E. coli O157:H7, total mesophilic aerobes, and yeasts and molds during storage were 0.8-1.5, 0.7-1.9, and 0.9-1.7 log CFU/g, respectively. DACP treatment, however, did not significantly affect the color, CO2 generation, weight, and surface morphology of lettuce during storage (P > 0.05). Some mesophilic aerobic bacteria were sublethally injured by DACP treatment. The results from this study demonstrate the potential of applying DACP as a post-packaging treatment to decontaminate lettuce contained in conventional plastic packages without altering color and leaf respiration during post-treatment cold storage.