Effect of Low-pressure Cold Plasma (LPCP) on the Wettability and the Inactivation of Escherichia coli and Listeria innocua on Fresh-Cut Apple (Granny Smith) Skin

Abstract

The aim of this study was to investigate the effect of low-pressure cold plasma (LPCP) on the inactivation of Escherichia coli and Listeria innocua on fresh-cut apple skin and its influence on wettability. Cold plasma treatments have shown to be effective to decontaminate foods, but their effect on the wettability has not been well studied. Surface-inoculated apple samples were treated with argon (Ar), nitrogen (N2), oxygen (O2), and argon-oxygen (Ar-O2) cold plasma using a commercial LPCP unit. Three different models were used to fit bacterial survival curves after the LPCP treatments. Changes in surface wettability were also determined by measuring the contact angle. The LPCP treatments using Ar, O2, or Ar-O2 mixture for 20 min were the most effective to inactivate E. coli with O2, while the LPCP treatment with N2 for 20 min reduced L. innocua the most for (p < 0.05). The highest increase in surface wettability was observed in samples treated for 20 min with O2 and Ar-O2. Different LPCP treatments have not great effectivity on the inactivation of E. coli and L. innocua on fresh-cut apple surface, but the all treatments changed the surface wettability of apples, making it more hydrophilic. This can be considered as a negative effect of the LPCP treatment because it can facilitate the adhesion and proliferation of re-contaminating microorganisms. More research should be undertaken to explore the use of other gases and complex surfaces.