Impact of cold plasma on Citrobacter freundii in apple juice: inactivation kinetics and mechanisms.
Various studies have shown that cold plasma is capable of inactivating microorganisms located on a variety of food surfaces, food packaging materials and process equipment under atmospheric pressure conditions; however, less attention has been paid to the impact of cold plasma on microorganisms in liquid foodstuffs. The present study investigates cold plasma's ability to inactivate Citrobacter freundii in apple juice. Optical emission spectroscopy (OES) and temperature measurements were performed to characterise the plasma source. The plasma-related impact on microbial loads was evaluated by traditional plate count methods, while morphological changes were determined using scanning electron microscopy (SEM). Physiological property changes were obtained through flow cytometric measurements (membrane integrity, esterase activity and membrane potential). In addition, mathematical modelling was performed in order to achieve a reliable prediction of microbial inactivation and to establish the basis for possible industrial implementation. C. freundii loads in apple juice were reduced by about 5 log cycles after a plasma exposure of 480s using argon and 0.1% oxygen plus a subsequent storage time of 24h. The results indicate that a direct contact between bacterial cells and plasma is not necessary for achieving successful inactivation. The plasma-generated compounds in the liquid, such as H2O2 and most likely hydroperoxy radicals, are particularly responsible for microbial inactivation.
Technische Universität Berlin, Department of Food Biotechnology and Food Process Engineering, Koenigin-Luise-Str. 22, 14195 Berlin, Germany.
Björn
B
Surowsky
Leibniz Institute for Agricultural Engineering Potsdam, Quality and Safety of Food and Feed, Max-Eyth-Allee 100, 14469 Potsdam, Germany.
Antje
A
Fröhling
Technische Universität Berlin, Department of Food Biotechnology and Food Process Engineering, Koenigin-Luise-Str. 22, 14195 Berlin, Germany.
Nathalie
N
Gottschalk
Leibniz Institute for Agricultural Engineering Potsdam, Quality and Safety of Food and Feed, Max-Eyth-Allee 100, 14469 Potsdam, Germany. Electronic address: oschlueter@atb-potsdam.de.
Oliver
O
Schlüter
Technische Universität Berlin, Department of Food Biotechnology and Food Process Engineering, Koenigin-Luise-Str. 22, 14195 Berlin, Germany.
Dietrich
D
Knorr
D001128:Argon / Q000494:pharmacology; D001628:Beverages / Q000382:microbiology*; D016971:Citrobacter freundii / Q000187:drug effects* / Q000502:physiology; D015169:Colony Count, Microbial; D005434:Flow Cytometry; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D027845:Malus / Q000382:microbiology*; D050296:Microbial Viability; D008954:Models, Biological; D010100:Oxygen / Q000494:pharmacology; D058626:Plasma Gases / Q000494:pharmacology*; D013696:Temperature; D013997:Time Factors
D058626:Plasma Gases; D001128:Argon; D006861:Hydrogen Peroxide; D010100:Oxygen
Atmospheric pressure plasma; Flow cytometry; Juice pasteurisation; Microbial inactivation; Non-thermal