Dielectric barrier discharge atmospheric cold plasma inhibits Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Tulane virus in Romaine lettuce

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 (~ 6 log CFU/g lettuce), or TV (~ 2 log PFU/g lettuce) and packaged in either a Petri dish (diameter: 150 mm, height: 15 mm) or a Nylon/polyethylene pouch (152 × 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 34.8 kV for 5 min and then analyzed either immediately or following post-treatment storage for 24 h at 4 °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 packaging type 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 for 24 h. Additionally, both rigid and flexible conventional plastic packages appear to be suitable for the in-package decontamination of lettuce with DACP.