Physicochemical properties and antimicrobial impacts of plasma‐activated simulated seawater onEscherichia coli

Abstract

Background: Some filter-feeding molluscan shellfish can concentrate harmful bacteria in their intestines during feeding, thus posing a potential food safety risk to human consumers. Plasma-activated simulated seawater (PASW) generated from non-thermal plasma may help reduce bacteria in live, molluscan shellfish when used as a disinfectant in depuration systems. This study determined the physicochemical properties of PASW and its antimicrobial efficacy against Escherichia coli DH5α. These results were then compared to similar data from a plasma-activated water (PAW) study.Results: PASW yielded temperatures ranging from 31.0 AE 0.2 to 49.7 AE 1.0 C, pH from 7.21 AE 0.0 to 2.70 AE 0.0, oxidation-reduction potential (ORP) from À15.7 AE 1.0 to 246.0 AE 0.9 mV, and electrical conductivity from 35.4 AE 0.3 to 48.1 AE 1.5 μS/cm after activation by plasma for 1-10 min. Temperature, ORP, electrical conductivity, nitrate (NO 3 À ), and nitrite (NO 2 À ) concentrations of PASW increased while pH decreased with increased plasma activation time. After 2-and 5-min incubations, E. coli treated with PASW5 and PASW10 both resulted in the highest reductions (~3 log CFU/ml). Further, while NO 3 À and NO 2 À concentrations in PASW were higher than in PAW of the same plasma exposure time, PAW yielded higher E. coli reduction values across treatments. Conclusion:Results from this study demonstrate the potential of PASW as a disinfectant for live, molluscan shellfish depuration to provide a microbiologically safer seafood product for human consumers.

Leveraging Plasma-Activated Seawater for the Control of Human Norovirus and Bacterial Pathogens in Shellfish Depuration

“…Focusing on PASWs, we successfully plasma-activated seawater using actual seawater, with demonstrated antimicrobial activity ( Figure 1 , Figure 2 , Figure 3 and Figure 4 ) and characterized by concentrations of NO 3 − similar to a previous study carried out using simulated seawater [ 63 ]. Importantly, the NO 3 − concentrations of PASW30 (310 mg/mL) ( Table 1 ) fall within the range reported to avoid adverse effects on clams’ and oysters’ viability (320 mg/mL) [ 65 ].…”

“…Only a few reports have investigated plasma-activated salt water or seawater, and its use for microbial inactivation [ 58 , 59 , 60 , 61 , 62 , 63 ]. Salt concentration affects electrical conductivity, and thus, it is directly related to the number of ions generated in solution during the plasma activation process.…”

“…Salt concentration affects electrical conductivity, and thus, it is directly related to the number of ions generated in solution during the plasma activation process. This contributes to the production of RONS and other antimicrobial compounds (e.g., singlet oxygen) responsible for microbial inactivation [ 11 , 63 , 64 ].…”

“…Indeed, the decrease in pH in PAW and PASW is attributed to the formation of inorganic acids (e.g., HNO 2 and HNO 3 ) that contribute to altering microbial and viral stability [ 66 , 67 , 68 , 69 , 70 , 71 ], while they can also affect shellfish viability [ 72 ]. Thus, PASW is diluted or buffered to prevent premature shellfish mortality [ 62 , 63 ]. However, the pH of PASW tested effectively in our study (PASW30 pH 5) is significantly different from pH < 3 reported previously [ 57 , 67 ].…”

“…However, the pH of PASW tested effectively in our study (PASW30 pH 5) is significantly different from pH < 3 reported previously [ 57 , 67 ]. This discrepancy is likely due to the diverse composition of seawater samples, with natural seawater carrying unidentified elements with buffering capacity (e.g., microalgae, organic matter, trace elements, or minerals) not included in the simulated seawater used by other authors [ 62 , 63 ].…”