Antimicrobial and cold plasma treatments for inactivation of listeria monocytogenes on whole apple surface

Authors: Ukuku, Dike; Niemira, Brendan; Uknalis, Joseph

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2017
Publication Date: 6/26/2017
Citation: Ukuku, D.O., Niemira, B.A., Uknalis, J. 2017. Antimicrobial and cold plasma treatments for inactivation of listeria monocytogenes on whole apple surface. [Abstract].Annual Meeting of the Institute of Food Technologists.Las Vegas, NV., Volume 1, Page 1.

Interpretive Summary:

Technical Abstract: Introduction: Produce and bacterial cell surface structure play an important role as to where and how bacteria attach to produce surfaces. The efficacy of a novel antimicrobial solution developed in our laboratory was investigated in combination with cold plasma treatments for inactivation of Listeria monocytogenes on whole apple surface. Purpose: The objective of this study was to investigate the inactivation of Listeria monocytogenes on apple calyx surfaces after treatments with antimicrobial solution followed by cold plasma treatments. Methods: Whole apples (Granny Smith) purchased from a supermarket were stored at room temperature (22C) for 18 h to come to room temperature. Apple surfaces were dipped in L. monocytogenes inoculums at 107 CFU/ml solution for 5 min, or by inoculating only the calyx area with 10 drops of 107 CFU/ml of the bacterial cells populations. After inoculation and a 2 h waiting period, L. monocytogenes populations determined was 4.5 log CFU/apple while aerobic mesophilic bacteria, and yeast and mold were 3.6 and 1.8, log CFU/apple respectively. Apples were treated as follows: 1) cold plasma treatments for 30 and 40s, 2) submersion of inoculated apples in antimicrobial solution for 5 min, 3) application of the antimicrobial solution directly to the calyx area, 4) addition of antimicrobial solution immediately followed by cold plasma treatments, 5) or cold plasma treatments immediately followed by addition of antimicrobial solution. Results: Antimicrobial solution treatments alone caused 1.8, 1.3 and 2 log reduction of aerobic mesophilic bacteria, yeast and mold and inoculated L. monocytogenes populations, respectively. Cold plasma treatments alone at 30 and 40s resulted in 1.33 and 2.41 log reduction of L. monocytogenes populations. A combination of the two treatments led to 4 log reduction. Scanning electron microscopy observation of treated calyx area showed morphological changes in bacterial cell structures. Surviving mesophilic and L. monocytogenes bacteria after combination treatments was <0.6 log CFU/g and <1 CFU/g, respectively. Yeast and mold populations were below detection limit. Significance: The results of this study suggests that a combination of cold plasma and antimicrobial solution treatments will significantly reduce bacteria attached at the calyx region thereby improving the microbial safety of apples.