Inactivation Efficacies and Mechanisms of Gas Plasma and Plasma-Activated Water against Aspergillus flavus Spores and Biofilms: a Comparative Study

Abstract

Atmospheric cold plasma (ACP) treatment is an emerging food technology for product safety and quality retention, shelf-life extension, and sustainable processing. The activated chemical species of ACP can act rapidly against microorganisms without leaving chemical residues on food surfaces. The main objectives of this study were to investigate the efficiency and mechanisms of inactivation of fungal spores and biofilms by ACP and to understand the effects of the gas-mediated and liquid-mediated modes of application against important fungal contaminants. Aspergillus flavus was selected as the model microorganism. A. flavus spores were exposed to either gas plasma (GP) or plasma-activated water (PAW), whereas gas plasma alone was used to treat A. flavus biofilms. This study demonstrated that both GP and PAW treatments independently resulted in significant decreases of A. flavus metabolic activity and spore counts, with maximal reductions of 2.2 and 0.6 log10 units for GP and PAW, respectively. The characterization of the reactive oxygen and nitrogen species in PAW and spore suspensions indicated that the concentration of secondary reactive species was an important factor influencing the antimicrobial activity of the treatment. The biofilm study showed that GP had detrimental effects on biofilm structure; however, the initial inoculum concentration prior to biofilm formation can be a crucial factor influencing the fungicidal effects of ACP. IMPORTANCE The production of mycotoxin-free food remains a challenge in both human and animal food chains. A. flavus, a mycotoxin-producing contaminant of economically important crops, was selected as the model microorganism to investigate the efficiency and mechanisms of ACP technology against fungal contaminants of food. Our study directly compares the antifungal properties of gas plasma (GP) and plasma-activated water (PAW) against fungi as well as reporting the effects of ACP treatment on biofilms produced by A. flavus.

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

“…Electrochemical changes of PAWM condensate were not unexpected and were demonstrated in many studies. [ 26,27,29 ] Acidizing of water and the increase of ORP and conductivity can be explained by the accumulation of plasma‐chemical reaction products in water (specifically HNO 2 , HNO 3 , H 2 O 2 , and HO 2 ).…”

“…The bactericidal effect of PAW depends on the incubation time and type of microorganism: prokaryotes (bacteria) are more susceptible than eukaryotes (fungi). [ 25–29 ]…”

Nonthermal plasma‐activated water: A comprehensive review of this new tool for enhanced food safety and quality

“…Recently, Los et al. (2020) also revealed the increase of extracellular MDA, DNA/RNA, and proteins after PAW treatment in the inactivation of Aspergillus flavus , indicating the release of intracellular materials following cell membrane disruption. The increase in extracellular nucleic acids and proteins could also be attributed to cell wall and membrane disruption (Los et al., 2020; Xiang et al., 2018).…”

“…The PAW pH has been reported to play a critical role in treatment (Naïtali et al., 2010; Y. M. Zhao et al., 2020). Los, Ziuzina, Boehm, Cullen, and Bourke (2020) recently conducted a comparison between PAW and acidified water (AW) at the same pH (∼2.4) and revealed that treatment with PAW and AW could reduce cell viability by 40.0 and 21.4% at contact times of 2 hr, respectively. While PAW was more effective against Aspergillus flavus spores than AW, it was not considered as the sole cause of these antibacterial properties (Korachi & Aslan, 2011; Traylor et al., 2011).…”

Plasma‐activated water: Physicochemical properties, microbial inactivation mechanisms, factors influencing antimicrobial effectiveness, and applications in the food industry

“…One of the main advantages of PAW as a novel disinfection technology compared to other technologies is that it is capable of inactivating a wide range of microorganisms, including bacteria (Thirumdas et al., 2018), biofilms (KamgangYoubi et al., 2008; Los, Ziuzina, Boehm, Cullen, & Bourke, 2020; Smet et al., 2019), spores (Bai et al., 2020; Sun et al., 2012), molds (Chen et al., 2019; Liu et al., 2020; Ma et al., 2016), yeasts (Guo et al., 2017; KamgangYoubi et al., 2009; Ryu et al., 2013), and even virus (Guo et al., 2018).…”