Inactivation of Enterobacter aerogenes on the surfaces of fresh-cut purple lettuce, kale, and baby spinach leaves using plasma activated mist (PAM)

Dielectric barrier discharge plasma-activated mist (PAM) is a surface treatment that has been shown to have antimicrobial effects on microorganisms attached to food contact surfaces. In this study, tryptic soy agar, purple lettuce, kale, and baby spinach leaves, were surface-inoculated with Enterobacter aerogenes inoculum (4 x 10(7) CFU/ml) and held for 30 min at room temperature (25 degrees C), then subsequently exposed to PAM in an enclosure (0.04 m(3)) from 5 to 20 min. Reductions ranging from 3.8 +/- 0.1 log CFU/plate to 5.6 +/- 0.3 log CFU/plate were observed on agar plates after exposure to PAM for 5 to 20 min. The leaves were either dip-inoculated or spot-inoculated. Extending PAM treatment time from 5 to 20 min increased microbial reduction on dip-inoculated leaves from 0.4 +/- 0.2, 0.8 +/- 0.1, and 0.9 +/- 0.1 log CFU/g to 0.9 +/- 0.1, 1.3 +/- 0.1, and 2.0 +/- 0.2 log CFU/g for purple lettuce, kale, and baby spinach leaves, respectively, and similar bacterial inactivations were observed on spot-inoculated leaves.