Dielectric barrier discharge atmospheric cold plasma inhibits Escherichia coli 0157:H7, Salmonella, Listeria monocytogenes, and Tulane virus in Romaine lettuce

Authors: MIN, SEA CHEOL - Seoul Women'S University; ROH, SI HYEON - Seoul Women'S University; Niemira, Brendan; Sites, Joseph; Boyd, Glenn; LACOMBE, ALISON - National College Of Natural Medicine

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2016
Publication Date: 8/23/2016
Citation: Min, S., Roh, S., Niemira, B.A., Sites, J.E., Boyd, G., Lacombe, A. 2016. Dielectric barrier discharge atmospheric cold plasma inhibits Escherichia coli 0157:H7, Salmonella, Listeria monocytogenes, and Tulane virus in Romaine lettuce. International Journal of Food Microbiology. 237:114–120.

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 pathogens Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Tulane virus (TV) on Romaine lettuce. Treatment parameters included moisture vaporization, modified atmospheric packaging (MAP), and post-treatment storage. Romaine lettuce was inoculated with E. coli O157:H7, Salmonella, L. monocytogenes (approximately 6 log CFU/g lettuce), or TV (approximately 2 log PFU/g lettuce) and packaged in either a Petri dish or a Nylon/polyethylene pouch with and without moisture vaporization. Additionally, a subset of pouch-packaged leaves was flushed with oxygen at 5% or 10% (balance of the gas was nitrogen). All of the packaged lettuce samples were treated with cold plasma at 47.6 kV for 5 min and then analyzed either immediately or following post-treatment storage for 24 h at 4 degrees C to assess the inhibition of microorganisms. Cold plasma inhibited E. coli O157:H7, Salmonella, L. monocytogenes, and TV by 92%, 60%, 90%, 95%, respectively. The inhibition of the bacteria was not significantly affected by the type of lettuce packaging or moisture vaporization (p > 0.05) but a reduced-oxygen MAP gas composition reduced the inhibition rates of E. coli O157:H7 and TV. L. monocytogenes continued to decline by an additional 75% in post-treatment cold storage. Both rigid and flexible conventional plastic packages appear to be suitable for the in-package decontamination of lettuce with this cold plasma system.

Technical Abstract: The present study investigated the effects of dielectric barrier discharge atmospheric cold plasma (DACP) treatment on the inactivation of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Tulane virus (TV) on Romaine lettuce, assessing the influences of moisture vaporization, modified atmospheric packaging (MAP), and post-treatment storage on the inactivation of these pathogens. Romaine lettuce was inoculated with E. coli O157:H7, Salmonella, L. monocytogenes (approximately 6 log CFU/g lettuce), or TV (approximately 2 log PFU/g lettuce) and packaged in either a Petri dish (diameter: 150 mm, height: 15 mm) or a Nylon/polyethylene pouch (152 x 254 mm) with and without moisture vaporization. Additionally, a subset of pouch-packaged leaves was flushed with O2 at 5% or 10% (balance N2). All of the packaged lettuce samples were treated with DACP at 47.6 kV for 5 min and then analyzed either immediately or following post-treatment storage for 24 h at 4 degres C to assess the inhibition of microorganisms. DACP treatment inhibited E. coli O157:H7, Salmonella, L. monocytogenes, and TV by 1.1 ± 0.4, 0.4 ± 0.3, 1.0 ± 0.5 log CFU/g, and 1.3 ± 0.1 log PFU/g, respectively, without environmental modifications of moisture or gas in the packages. The inhibition of the bacteria was not significantly affected by the type of lettuce packaging or moisture vaporization (p > 0.05) but a reduced-oxygen MAP gas composition attenuated the inhibition rates of E. coli O157:H7 and TV. L. monocytogenes continued to decline by an additional 0.6 log CFU/g in post-treatment cold storage. Additionally, both rigid and flexible conventional plastic packages appear to be suitable for the in-package decontamination of lettuce with DACP.