Nisin-based antimircobial combination with cold plasma treatment inactivate Listeria monocytogenes on Granny Smith apples

Abstract

A nisin-based antimicrobial and cold plasma combination treatments in reducing Listeria monocytogenes inoculated on apple surfaces purchased from a New Jersey farm and a supermarket in Philadelphia area was investigated. All apples were spot inoculated or by submersion in 107 CFU/ml L. monocytogenes inoculum. Populations of L. monocytogenes recovered on farm and supermarket apples after spot inoculation averaged 5.8 ± 0.24 log CFU/g and 4.6 ± 0.12 log CFU/g, respectively and 4.1 ± 0.22 log CFU/g and 3.6 ± 0.12 log CFU/g, respectively on submerged apples. All apples were treated with antimicrobial solution for 30 s, 40 s, 3 min (180s) and 1 h (3600 s), cold plasma treatments for 30 and 40s, and a combination of antimicrobial and cold plasma treatments and the surface structure of apples were examined using scanning electron microscopy (SEM). Cold plasma treatment at 40s, followed immediately with antimicrobial treatments at 180s and 3600 s led to 2.5 and 4.6 log CFU/g inactivation of L. monocytogenes, respectively. SEM observation showed changes on apple surface structures but not on bacterial cell structure. This result suggests that this combination treatments is effective in killing L. monocytogenes on apple surfaces.