Inactivation of Single Strains of Listeria monocytogenes and Salmonella Typhimurium Planktonic Cells Biofilms With Plasma Activated Liquids

Abstract

Recent research has proven the ability of cold atmospheric plasma (CAP) for assuring food safety. A more flexible and transportable alternative is the use of plasma activated liquids (PAL), which are also known to have antimicrobial properties. However, within the context of food safety, little is known on its potential regarding decontamination. This research therefore focusses on identifying the impact of (i) the microbial species and its cell type (planktonic cells or biofilms), (ii) the CAP settings (i.e., gas composition and generation time) and (iii) PAL related factors (treatment time and PAL age) on the technologies efficacy. Cell densities were monitored using the plate counting technique for which the results were analyzed by means of predictive inactivation models. Moreover, the pH and the concentrations of long-lived species (i.e., hydrogen peroxide, nitrite, and nitrate) were measured to characterize the PAL solutions. The results indicated that although the type of pathogen impacted the efficacy of the treatment, mainly the cell mode had an important effect. The presence of oxygen in the operating gas ensured the generation of PAL solutions with a higher antimicrobial activity. Moreover, to ensure a good microbial inactivation, PAL generation times needed to be sufficiently long. Both CAP related factors resulted in a higher amount of long-lived species, enhancing the inactivation. For 30 min. PAL generation using O 2 , this resulted in log reductions up to 3.9 for biofilms or 5.8 for planktonic cells. However, loss of the PAL activity for stored solutions, together with the frequent appearance of a tailing phase in the inactivation kinetics, hinted at the importance of the short-lived species generated. Different factors, related to (i) the pathogen and its cell mode, (ii) the CAP settings and (iii) PAL related factors, proved to impact the antimicrobial efficacy of the solutions and should be considered with respect to future applications of the PAL technology.

Inactivation efficacy and mechanisms of plasma activated water on bacteria in planktonic state

“…Around 5 log reduction was obtained after 30-min exposure with PAW immediately after generation. Smet et al (2019) studied the inactivation efficacy of PAW against L. monocytogenes and Salmonella Typhimurium in planktonic and biofilm state using a cold atmospheric plasma, along with which the impact of different gas composition, PAW generation time and exposure time were investigated. The results showed that L. monocytogenes were more resistant to PAW than S. Typhimurium when treated by the same conditions, and bacteria in planktonic state was easier to inactivate than biofilm state for both species.…”

“…Plasma activated water (PAW) is generated from plasma treatment of water. Recently, PAW has attracted considerable attention as it has been reported to be effective against a wide range of micro-organisms, including bacteria (Kamgang-Youbi et al 2009;Ercan et al 2013;Smet et al 2019), biofilms (Kamgang-Youbi et al 2008;Chen et al 2017;Govaert et al 2019), spores (Sun et al 2012) and yeasts (Ryu et al 2013;Guo et al 2017). There are several advantages of using PAW for microbial inactivation.…”

“…For processing parameters, applied voltage, plasma treatment time for PAW generation (Zhang et al 2017), exposure time of bacteria with PAW (Ursache et al 2014), treatment model (direct or indirect) (Han et al 2016a), feeding gases and air flow rate (Girard et al 2018;Machala et al 2018) should all be considered. Microbial parameters include the type and state of the micro-organism, for example, vegetative bacteria or spores, planktonic or detached state (Kamgang-Youbi et al 2008;Smet et al 2019), and the microbial community on food products may also affect the inactivation efficacy. Regarding abiotic parameters, storage temperature for PAW (Shen et al 2016;Han et al 2016b), the presence of organic materials in water (Ryu et al 2013;Xiang et al 2019;Zhao et al 2020), and the surface morphology of food products (Royintarat et al 2020) should be considered.…”

Bidirectional mass transfer‐based generation of plasma‐activated water mist with antibacterial properties

“…There are many different approaches to PAW generation: one is to induce the plasma directly into the water and the second one involves discharges over water and hydrated surfaces [ 25,32–35 ] or gas discharge in bubbles. [ 36 ] The main disadvantage limiting the use of PAW for decontamination is the long treatment time: It takes 5–30 min on average to achieve a 4–6 log reduction in viability of bacteria.…”

“…[ 36 ] The main disadvantage limiting the use of PAW for decontamination is the long treatment time: It takes 5–30 min on average to achieve a 4–6 log reduction in viability of bacteria. [ 25,31,32 ] In all conducted experiments, activated water was added to the bacterial suspension or contaminated objects (plates with adhesive bacteria) were immersed in it. Thus, it is necessary to further drain the objects during the practical application of PAW in food industry, for example, which requires additional labor and time.…”