Nitrogen Accumulation in Oyster (Crassostrea gigas) Slurry Exposed to Virucidal Cold Atmospheric Plasma Treatment

Abstract

Viral contamination of edible bivalves is a major food safety issue. We studied the virucidal effect of a cold atmospheric plasma (CAP) source on two virologically different surrogate viruses [a double-stranded DNA virus (Equid alphaherpesvirus 1, EHV-1), and a single-stranded RNA virus (Bovine coronavirus, BCoV)] suspended in Dulbecco’s Modified Eagle’s Medium (DMEM). A 15 min exposure effectuated a statistically significant immediate reduction in intact BCoV viruses by 2.8 (ozone-dominated plasma, “low power”) or 2.3 log cycles (nitrate-dominated, “high power”) of the initial viral load. The immediate effect of CAP on EHV-1 was less pronounced, with “low power” CAP yielding a 1.4 and “high power” a 1.0 log reduction. We observed a decline in glucose contents in DMEM, which was most probably caused by a Maillard reaction with the amino acids in DMEM. With respect to the application of the virucidal CAP treatment in oyster production, we investigated whether salt water could be sanitized. CAP treatment entailed a significant decline in pH, below the limits acceptable for holding oysters. In oyster slurry (a surrogate for live oysters), CAP exposure resulted in an increase in total nitrogen, and, to a lower extent, in nitrate and nitrite; this was most probably caused by absorption of nitrate from the plasma gas cloud. We could not observe a change in colour, indicative for binding of NOx to haemocyanin, although this would be a reasonable assumption. Further studies are necessary to explore in which form this additional nitrogen is deposited in oyster flesh.

Effect of Plasma On-Time with a Fixed Duty Ratio on Reactive Species in Plasma-Treated Medium and Its Significance in Biological Applications

“…Some studies have demonstrated that the impacts of NTAPP are significantly selective for cancer cells. The pH of the PTM remained unchanged after NTAPP, which is identical to our results [ 46 , 47 ]. The DMEM has the capacity to maintain the pH and temperature of the PTM [ 48 ].…”

Antimicrobial Effects of Plasma-Activated Simulated Seawater (PASW) on Total Coliform and Escherichia coli in Live Oysters during Static Depuration

“…Considering the novelty of this study, these results and preliminary results can provide a basis for future studies of PASW-oyster depuration efforts (Supplementary Figure S1). However, a few studies have examined cold atmospheric plasma applied directly to oyster meat [45,46]. In the study by Csadek et al (2021), their cold atmospheric plasma treatment inactivated enveloped RNA virus in blended oyster meat slurry.…”

Treatment of Fresh Meat, Fish and Products Thereof with Cold Atmospheric Plasma to Inactivate Microbial Pathogens and Extend Shelf Life

“…Csadek et al [ 134 ] studied the inactivation of surrogate viruses on an oyster slurry, but employed a DBD instead of a jet-type plasma generator. Plasma was generated from ambient air.…”

“…Both Choi et al [ 133 ] and Csadek et al [ 134 ] studied oyster tissue and not live oyster, and it was a contamination scenario, not an infection. However, the antiviral effects of CAP exposure can also be expected for live oysters, whereas the significance of the observed nitrogen accumulation in oyster slurry for live animals is not entirely clear.…”

“…Although the concept of applying CAP to reduce viral contamination in water is promising [ 136 ], it will largely depend on the composition of the plasma species. When NO x are generated, they will be dissolved in water and lower the pH [ 134 ]. This pH drop is an additional stressor for the oysters.…”